Optimized Design of the Waveguide Layers for GaN-Based QW Red Lasers

Optimized Design of the Waveguide Layers for GaN-Based QW Red Lasers | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Optimized Design of the Waveguide Layers for GaN-Based QW Red Lasers ZHONGQIANG GE, MEI ZHOU, YACHEN WANG, JIANKAI SUN, DEGANG ZAHO, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9299993/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract The threshold current of GaN-based quantum well(QW) red lasers is modulated by modifying the In composition of InGaN waveguide layers and adjusting the thickness and structure of waveguide layers. Theoretical analysis based on LASTIP calculations reveals that the In composition for achieving the best threshold current increases initially with increasing laser wavelength, but when the wavelength reaches up to a value, it turns to decrease. Additionally, for the 636 nm GaN-based red laser, the threshold current decreases with increasing waveguide layer thickness. Furthermore, the threshold current for lasers with a stepped waveguide structure of the same total thickness is lower than that for a single-layer waveguide. This work provides a new approach for structural optimization of GaN-based QW red lasers. GaN-based red lasers Waveguide layers Optical field Threshold current Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The bandgap width of GaN-based materials is continuously tunable from InN (0.7eV) to AlN (6.2eV), covering the entire visible spectrum[ 1 , 2 ]. GaN-based lasers offer advantages such as compact size, high efficiency, and extended lifetime, making them ideal candidates for full-color micro-laser light-emitting diodes. Currently, blue quantum well(QW) laser fabrication techniques based on GaN have been relatively mature[ 3 ]. Although the fabrication of green QW lasers presents significant technical challenges, they have also matured in recent years[ 4 – 6 ].The successful development of GaN-based red QW lasers would enable the integration of red, green, and blue primary color lasers within a single material system. This integration would streamline manufacturing processes, reduce costs and complexity, enhance device lifetime, reliability, and operational efficiency, thereby laying the foundation for future development of ultra-compact, high-performance monolithic integrated microdisplay chips[ 7 , 8 ]. Achieving efficient long-wavelength lasing in GaN-based QW materials presents a fundamental difficulty: increasing the emission wavelength requires raising the indium (In) composition in the InGaN quantum well active region to reduce the bandgap, which in turn escalates the growth challenges of the active region and introduces substantial lattice mismatch, leading to a significant drop in external quantum efficiency (EQE). Furthermore, for red lasers,the emission peak wavelength shift caused by the internal electric field is more severe than those caused in blue and green LDs. [ 9 – 11 ] These factors collectively degrade crystal quality, increase defect density, raise the laser threshold current, and impede improvements in efficiency, output power, and device lifetime.[ 12 – 15 ]. The waveguide layers in laser structure serve to effectively confine generated laser photons within the active region, facilitating strong interaction with charge carriers (electrons and holes) to achieve efficient stimulated emission and laser output. They constitute one of the indispensable key structures enabling GaN-based lasers to operate with low threshold, high efficiency, and superior performance[ 16 , 17 ].In this paper, we shall investigate the influence of different parameters of InGaN waveguide layers, including In composition, layer thickness and structure, on the threshold current of lasers using the professional simulation software LASTIP. Laser structure and simulation parameters The schematic diagram of the red QW laser structure employed in this study is shown in Fig. 1.The laser diode (LD) comprises a 1µm GaN substrate (Si: 1×10²⁴/m³), a 1µm AlGaN cladding (Si: 1×10²⁴/m³), a 0.12µm In x Ga 1−x N lower waveguide layer (Si: 1×10²⁴/m³),an InGaN/GaN multiple quantum well (MQW) active region, a 0.1µm In x Ga 1−x N upper waveguide layer (Mg: 5×10²²/m³), a 0.005µm \(\:\text{A}{\text{l}}_{0.03}\text{G}{\text{a}}_{0.97}\text{N}\) electron barrier layer (Mg: 1×10²⁵/m³), 0.45µm AlGaN cladding layer (Mg: 1×10²⁵/m³), 0.15µm p-GaN layer (Mg: 1×10²⁵/m³), and 0.04µm highly doped p ++ -GaN contact layer (Mg: 1×10²⁶/m³).Additionally, the LD device employs a rectangular waveguide structure with a ridge width and cavity length set at 3 µm and 600 µm respectively. Software LASTIP is a specialized TCAD (Technology Computer-Aided Design) tool for simulating semiconductor lasers, primarily used to design and analyze the performance of semiconductor optoelectronic devices such as edge-emitting lasers and surface-emitting lasers. The software possesses robust multi-physics coupling simulation capabilities, enabling simultaneous handling of electrical, optical, and thermal simulations, as well as steady-state and transient characteristics[ 18 – 20 ]. It effectively models current-voltage characteristics and output power of laser diode devices. During calculations, both p-type and n-type electrodes are treated as ideal ohmic contacts, with the operating temperature set at 300 K. As defect charges and interface charges partially counteract the built-in polarization effect, interface charge values derived from the Fiorentini theoretical model typically exceed experimental values by 20%, 50%, or 80%[ 21 – 23 ]. Consequently, this study sets the polarization electric field to 25% of the theoretical value. In our simulations, the refractive indices of Al x Ga 1−x N and In x Ga 1−x N materials were calculated using the following formula[ 24 ]: $$\:n（A{l}_{x}G{a}_{1-x}N）=\left[n\right(AlN)-n(GaN\left)\right]x+n\left(GaN\right)$$ $$\:n（I{n}_{x}G{a}_{1-x}N）=\left[n\right(InN)-n(GaN\left)\right]x+n\left(GaN\right)$$ where the refractive indices for AlN, GaN, and InN are 2.247, 2.435, and 2.879 respectively. Furthermore, we defined the absorption coefficient of different layers as a function of doping concentration, expressed as follows[ 25 ]: $$\:{\text{a}}_{\text{i}}=\text{d}\text{o}\text{p}\text{i}\text{n}\text{g}\:\text{c}\text{o}\text{n}\text{c}\text{e}\text{n}\text{t}\text{r}\text{a}\text{t}\text{i}\text{o}\text{n}\left(\text{c}{\text{m}}^{-3}\right)/(1\ast\:1{0}^{19}(\text{c}{\text{m}}^{-3})\times\:50(\text{c}{\text{m}}^{-1}\left)\right)$$ Figure_1 Schematic diagram of the laser structure Results and discussion First, we employed LASTIP to calculate the lower threshold current of the P-I curve for the structure in Fig. 1 across different wavelengths. The lasing wavelength is dependent on the parameter selection of the QW active region. The threshold current represents the minimum injection current required for the laser to initiate stimulated emission (i.e., lasing). Only when the injection current exceeds this threshold, laser oscillation can occur, generating stimulated radiation through feedback within the optical resonator. This result in coherent laser emission is characterized by excellent directionality, high monochromaticity, and exceptional brightness. A lower threshold current indicates an easier lasing initiation, and normally also a higher energy conversion efficiency, alongside reduced operating temperatures and extended device lifetime. Figure 2 displays the P-I curves for the laser structure shown in Fig. 1 at different wavelengths under minimum threshold conditions. Overall, the laser's threshold current exhibits a continuous increase with increasing wavelength. Figure 2(a) and (b) depict the obtained P-I curves near 550 nm and 600 nm, respectively, with threshold currents of 34 mA and 36 mA near these two wavelengths. Compared to 550 nm, the threshold current at 600 nm increases by 2 mA. Figure_2(a): P-I curve near 550 nm; (b): P-I curve near 600 nm Subsequently, we seek to grow high-quality long-wavelength lasers by changing the composition of waveguide layers. For this purpose, we have fixed the thickness of the upper waveguide at 100 nm and the thickness of the lower waveguide at 120 nm. Figure 3 shows the optimal In composition of the waveguide layers corresponding to obtaining the best threshold current at different wavelengths. A comparison reveals that the In composition required in the waveguide layers for reaching the lowest threshold current continuously increases with increasing wavelength, but it decreases when the wavelength increases beyond 616 nm. We then calculated the optical field distribution for lasers operating above 616 nm, between 616 nm and 656 nm, as shown in Fig. 3(b). These distribution curves revealed a shift in the optical field distribution, which should be the primary factor driving the required In composition decrease beyond 616 nm. Figure_3 (a) In composition of the waveguide layers corresponding to the optimum threshold current, (b) The shifts of light field distribution curves obtained at different wavelengths, where the inset is an amplification of the top part of these curves. On the other hand, we consider that the thickness of the waveguide layers can also significantly influence the threshold current of long-wavelength lasers. We conducted a comparative study on the influence of thicknesses of both upper and lower waveguide layers. For this purpose, we fixed the In composition of both InGaN upper and lower waveguide layers to 0.078. First, we investigated the effect of varying upper and lower waveguide thicknesses on the optical characteristics of a 636 nm GaN-based laser. Figures 4(a) and (b) display the optical field distributions at a 150 mA current for varying thickness of upper or lower waveguide layers, respectively, where only one side's waveguide thickness is altered. The peak intensity on the right side ( around the active region and the upper waveguide) is markedly higher than that on the left side (around the lower waveguide region and the substrate side region,). It is noted that as the waveguide layer thickness increases, the peak intensity on the left side becomes markedly lower than that on the right. The slight displacement of the optical field in Fig. 4(b) arises because the position of the quantum well shifts as the lower waveguide thickens. These results indicate that an increased waveguide thickness, for both upper and lower waveguide layers, may enhance optical confinement, thereby suppressing field leakage and improving the optical performance of the 636 nm GaN-based laser. Figure_4 (a) Normalized Light field distribution when upper waveguide thickness changes (b) Normalzed light field distribution when lower waveguide thickness changes. In the figures, the right side peaks are located around the active region, the left side peaks are located in the lower waveguide region. Subsequently, we investigated the relationship between output power and injection current (P-I curve) of a 636 nm GaN-based laser when varying only one-sided waveguide layer thickness, i.e. upper and lower waveguide layer thickness, as shown in Figs. 5(a) and 5(c), respectively. Figures 5(b) and 5(d) present the data of dependence of lasing threshold current on the thickness of upper and lower waveguide layer while the thickness of other waveguide is not changed. Upon increasing the injection current to threshold current, the devices start lasing. After lasing, the laser output power exhibit a sharp rise. It is found that as the injection current continues to increase, the output power of lasers is significantly improved with increasing waveguide thickness, as shown in Fig. 5 (a) and (c).As the waveguide layer thickness increases, the threshold injection current for laser operation decreases as shown in Fig. 5(b) and (d). However, it is noted ,as shown in the Fig. 5 ( d ) when the lower waveguide thickness increases up to beyond 300 nm, the threshold current begins to increase slightly. To find its reason, we calculated the optical confinement factor (OCF)and internal absorption loss ༈IAL༉for lasers in which lower waveguide layer thickness changes in the range between 260 nm to 340 nm. The results are presented in Table 1 . It is found that when the lower waveguide layer becomes much thicker, the center of optical field distribution curve shifts downward. This reduces the proportion of overlapping field energy in the active region, thereby decreasing the optical confinement factor (Γ). At the same time, the internal absorption loss exhibits a trend of gradually increases. As a whole, the threshold current shows a slight increase due to the combined effects of these two factors. In summary, if the waveguide thickness is not too large, increasing the waveguide layer thickness effectively reduces the threshold current, thereby significantly improving the electrical performance of InGaN-based red light-emitting laser diodes. Figure_5 (a) P-I curves corresponding to different thicknesses of upper waveguide layer; (b) The data points for threshold current under varying upper waveguide thicknesses (*) for a 636 nm laser structure. Figure_5 (c) P-I curves corresponding to different lower waveguide thicknesses; (d) Data points of threshold currents for different thicknesses(*) of lower waveguide layer Table 1 Optical confinement factor and internal absorption loss corresponding to different lower waveguide layer thicknesses LWG Thickness (nm) 260 280 300 320 340 OCF(10 − 2 ) 0.559 0.573 0.580 0.585 0.586 IAL(10 4 /cm) 0.136 0.139 0.142 0.145 0.147 To further investigate the influence of waveguide layer structure on laser performances, we propose a stepped waveguide structure. A 636 nm laser was selected as a representative example. In the stepped laser structure, the thickness of upper waveguide layer is fixed to be 100 nm. Both upper and lower waveguide layers are divided into two parts with equal thickness, but with different In compositions,(the In component near the active region is 0.078, while the In component away from the active region is 0.048.) Then the P-I curves have been calculate and shown in Fig. 6(a) where the total thickness of lower waveguide layer increases from 120 nm to 260 nm. Figure 6(b) shows the corresponding data points of the threshold current of these laser structures. Figure 6(c) displays the corresponding optical field distributions. The obtained results indicate that, at equivalent thicknesses, the threshold current behavior of the lasers with stepped waveguide layers significantly outperforms that with single-layered waveguide structure. It can be seen from a comparison between the curve shown in Fig. 6 (b) with the curve shown in Fig. 5 (d), the threshold current value is lower for stepped structure laser. In fact ,in both cases the threshold current continues to decrease as the thickness difference increases. Furthermore, even with stepped waveguide structure part of In composition is reduced from 0.78 to 0.48, with a lower total In composition in the lower waveguide layer, the lasers with stepped waveguide still exhibit a better optical confinement and a reduced light leakage compared to lasers with single-layer waveguide structure. Figure_6 (a) P-I curves of 636 nm lasers with stepped waveguides of different total thicknesses of er waveguide layer. Threshold currents for lasers with stepped waveguides of corresponding thicknesses, (c)Normalized Light field Distribution in Stepped Waveguides of Different lower waveguide thicknesses Conclusion In summary, we designed and calculated the influences of InGaN waveguide layers In composition on laser performances at different wavelengths using LASTIP simulation software.The study revealed that, in overall, as the laser wavelength increases, the In composition in the waveguide layer required for the best threshold current continuously rises, and the threshold current also gradually increases. We investigated the effects of varying thickness and waveguide layer structure on the threshold current of 636 nm red lasers. The results show that with a lower average. In content, stepped waveguide layers of the same total thickness actually provide better optical field confinement and lower threshold current. Declarations Disclosures. The authors declare no conflicts of interest. Author Contribution Z.G. and M.Z. and D.Z. conceived the study. Z.G. designed the experiments and performed the measurements. Z.G. and J.S. developed the analytical software. Z.G. and Y.W. performed the data analysis. X.W. and X.Z. contributed to data collection and validation. Z.G. wrote the original draft. Z.G. and M.Z. and D.Z. reviewed and edited the manuscript. M.Z. supervised the project and acquired funding. All authors read and approved the final manuscript. Data Availability Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request. References Ben, Y., et al.: Different influence of InGaN lower waveguide layer on the performance of GaN-based violet and ultraviolet laser diodes. Superlattices Microstruct. 133 , 8 (2019) Wu, J.: When group-III nitrides go infrared: New properties and perspectives. J. Appl. Phys. 106 , 28 (2009) Wong, M., et al.: High efficiency of III-nitride micro-light-emitting diodes by sidewall passivation using atomic layer deposition. Opt. Express. 26 , 21324–21331 (2018) Jiang, X., et al.: Study on the performance of InGaN-based green LED by designing different preparing layers. Opt. Mater. 89 , 505–511 (2019) Li, P., et al.: Very high external quantum efficiency and wall-plug efficiency 527 nm InGaN green LEDs by MOCVD. Opt. Express. 26 , 33108–33115 (2018) Lv, Q., et al.: Realization of Highly Efficient InGaN Green LEDs with Sandwich-like Multiple Quantum Well Structure: Role of Enhanced Interwell Carrier Transport. ACS Photonics. 6 , 130–138 (2019) Bi, Z., et al.: In: Jiang, H., Lin, J. (eds.) From nanoLEDs to the realization of RGB-emitting microLEDs, in Micro Leds , pp. 223–251. Elsevier Academic Press Inc, San Diego (2021) Hsiang, E., et al.: Prospects and challenges of mini-LED, OLED, and micro-LED displays. J. Soc. Inf. Disp. 29 , 446–465 (2021) Iida, D., et al.: Demonstration of low forward voltage InGaN-based red LEDs. Appl. Phys. Express. 13 , 4 (2020) Iida, D., et al.: 633-nm InGaN-based red LEDs grown on thick underlying GaN layers with reduced in-plane residual stress. Appl. Phys. Lett. 116 , 5 (2020) Zhang, S., et al.: Efficient emission of InGaN-based light-emitting diodes: toward orange and red. Photonics Res. 8 , 1671–1675 (2020) Koukitu, A., et al.: Thermodynamic analysis of the MOVPE growth of InxGa1-xN. J. Cryst. Growth. 170 , 306–311 (1997) Yamashita, Y., et al.: Control of emission wavelength of GaInN single quantum well, light emitting diodes grown hy metalorganic chemical vapor deposition in a split-flow reactor, Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Brief Commun. Rev. Pap. 42, 4197–4202 (2003) Shimizu, M., et al.: Metalorganic vapor phase epitaxy of thick InGaN on sapphire substrate, Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Brief Commun. Rev. Pap. 36, 3381–3384 (1997) Holec, D., et al.: Critical thickness calculations for InGaN/GaN. J. Cryst. Growth. 303 , 314–317 (2007) Wang, X., et al.: The influence of material quality of lower InGaN waveguide layer on the performance of GaN-based laser diodes. Appl. Surf. Sci. 570 , 6 (2021) Wang, W., et al.: Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers. Chin. Phys. B. 31 , 6 (2022) Xing, Y., et al.: Suppression of electron and hole overflow in GaN-based near-ultraviolet laser diodes. Chin. Phys. B. 27 , 6 (2018) Hou, Y., et al.: Characteristics of InGaN-based green laser diodes with additional InGaN hole reservoir layer. Vacuum. 186 , 7 (2021) Liang, F., et al.: Output light power of InGaN-based violet laser diodes improved by using a u-InGaN/GaN/AlGaN multiple upper waveguide. Chin. Phys. B. 26 , 5 (2017) Chichibu, S., et al.: Effective band gap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures. Appl. Phys. Lett. 73 , 2006–2008 (1998) Zhang, H., et al.: Measurement of polarization charge and conduction-band offset at InxGa1-xN/GaN heterojunction interfaces. Appl. Phys. Lett. 84 , 4644–4646 (2004) Renner, F., et al.: Quantitative analysis of the polarization fields and absorption changes in InGaN/GaN quantum wells with electroabsorption spectroscopy. Appl. Phys. Lett. 81 , 490–492 (2002) Zhang, L., et al.: Confinement factor and absorption loss of AlInGaN based laser diodes emitting from ultraviolet to green. J. Appl. Phys. 105 , 8 (2009) Huang, C., et al.: Optical waveguide simulations for the optimization of InGaN-based green laser diodes. J. Appl. Phys. 107 , 7 (2010) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 03 Apr, 2026 Editor assigned by journal 03 Apr, 2026 Submission checks completed at journal 03 Apr, 2026 First submitted to journal 02 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9299993","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":617164186,"identity":"3384d3c7-27e7-4aed-ba4b-28afd4b0f48c","order_by":0,"name":"ZHONGQIANG GE","email":"","orcid":"","institution":"China Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"ZHONGQIANG","middleName":"","lastName":"GE","suffix":""},{"id":617164187,"identity":"8b0967b4-f5d4-4503-afee-9d3b0875f0a3","order_by":1,"name":"MEI ZHOU","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAn0lEQVRIiWNgGAWjYJACZiCWY2NvPkCaFmM+nmMJpGlJnCeRo0Ccct1pp5M/F1QcTm9jyGFg+FGxjbAWs9u5G4xnnDmc28Zw9gBjz5nbxGlJ5m0DamHsS2BmbCNSy2GglnQ2Zh4DorVsbAZqSWBjI0HLZmaeM+mGbTxsCQeJ9cvmzzwV1vLy8x8ffPCjgggtKOAAiepHwSgYBaNgFOACAPVjO1IGLt0CAAAAAElFTkSuQmCC","orcid":"","institution":"China Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"MEI","middleName":"","lastName":"ZHOU","suffix":""},{"id":617164188,"identity":"6a13187b-b522-45c6-8421-7ac7cbc15a17","order_by":2,"name":"YACHEN WANG","email":"","orcid":"","institution":"Chinese Academy of Science","correspondingAuthor":false,"prefix":"","firstName":"YACHEN","middleName":"","lastName":"WANG","suffix":""},{"id":617164189,"identity":"3e7cb3f5-f1af-4f68-84b2-60a65ed04320","order_by":3,"name":"JIANKAI SUN","email":"","orcid":"","institution":"Chinese Academy of Science","correspondingAuthor":false,"prefix":"","firstName":"JIANKAI","middleName":"","lastName":"SUN","suffix":""},{"id":617164190,"identity":"7da72598-ab8e-4b3c-be7d-f85bef90b334","order_by":4,"name":"DEGANG ZAHO","email":"","orcid":"","institution":"Chinese Academy of Science","correspondingAuthor":false,"prefix":"","firstName":"DEGANG","middleName":"","lastName":"ZAHO","suffix":""},{"id":617164191,"identity":"c941c75f-c614-42cc-a0c5-96cab3b22076","order_by":5,"name":"XINGXIAN WU","email":"","orcid":"","institution":"China Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"XINGXIAN","middleName":"","lastName":"WU","suffix":""},{"id":617164192,"identity":"1da7348c-be2e-4207-956a-f5b1dcb5d3c4","order_by":6,"name":"XIN ZHOU","email":"","orcid":"","institution":"China Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"XIN","middleName":"","lastName":"ZHOU","suffix":""}],"badges":[],"createdAt":"2026-04-02 08:08:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9299993/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9299993/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107347779,"identity":"9f739801-d099-46fa-b583-5d4518f88c18","added_by":"auto","created_at":"2026-04-20 15:28:42","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":114083,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the laser structure\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/d12551791a1fbcf3db242617.png"},{"id":107484852,"identity":"82c8b160-df6a-46cc-bd4e-a99d18d1f004","added_by":"auto","created_at":"2026-04-22 02:33:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87867,"visible":true,"origin":"","legend":"\u003cp\u003e(a): P-I curve near 550 nm; (b): P-I curve near 600 nm\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/83de92cc3bf5ddaeaa8c1265.png"},{"id":107347781,"identity":"0da2e718-9071-4e1a-bf1c-f33b1224fef0","added_by":"auto","created_at":"2026-04-20 15:28:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":88793,"visible":true,"origin":"","legend":"\u003cp\u003e(a) In composition of the waveguide layers corresponding to the optimum threshold current , (b) The shifts of light field distribution curves obtained at different wavelengths, where the inset is an amplification of the top part of these curves.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/c45b9faedcce90cde1680fde.png"},{"id":107347784,"identity":"feaac234-a7bb-49e5-945b-0e12f20dd25e","added_by":"auto","created_at":"2026-04-20 15:28:43","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":154287,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Normalized Light field distribution when upper waveguide thickness changes (b) Normalzed light field distribution when lower waveguide thickness changes. In the figures, the right side peaks are located around the active region, the left side peaks are located in the lower waveguide region.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/69d829b9401dd43d550b17e6.png"},{"id":107347782,"identity":"0612db58-3a2a-493c-9024-ee5d97312c99","added_by":"auto","created_at":"2026-04-20 15:28:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":100911,"visible":true,"origin":"","legend":"\u003cp\u003e(a) P-I curves corresponding to different thicknesses of upper waveguide layer; (b) The data points for threshold current under varying upper waveguide thicknesses (*) for a 636 nm laser structure.\u003c/p\u003e\n\u003cp\u003e(c) P-I curves corresponding to different lower waveguide thicknesses; (d) Data points of threshold currents for different thicknesses(*) of lower waveguide layer\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/209c757e50af1d3ef3addb38.png"},{"id":107487252,"identity":"2e59f8fc-e61e-4af4-bbed-58f5906e1c6d","added_by":"auto","created_at":"2026-04-22 02:40:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":149227,"visible":true,"origin":"","legend":"\u003cp\u003e(a) P-I curves of 636 nm lasers with stepped waveguides of different total thicknesses of er waveguide layer. Threshold currents for lasers with stepped waveguides of corresponding thicknesses，（c）Normalized Light field Distribution in Stepped Waveguides of Different lower waveguide thicknesses\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/88acd0e421dd601781bcde53.png"},{"id":107488660,"identity":"709c68a3-0f6a-44a2-94cc-57ff203f5013","added_by":"auto","created_at":"2026-04-22 02:45:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":784902,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9299993/v1/384e8f70-65ca-4694-b325-244028cd458d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimized Design of the Waveguide Layers for GaN-Based QW Red Lasers","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe bandgap width of GaN-based materials is continuously tunable from InN (0.7eV) to AlN (6.2eV), covering the entire visible spectrum[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. GaN-based lasers offer advantages such as compact size, high efficiency, and extended lifetime, making them ideal candidates for full-color micro-laser light-emitting diodes. Currently, blue quantum well(QW) laser fabrication techniques based on GaN have been relatively mature[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Although the fabrication of green QW lasers presents significant technical challenges, they have also matured in recent years[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].The successful development of GaN-based red QW lasers would enable the integration of red, green, and blue primary color lasers within a single material system. This integration would streamline manufacturing processes, reduce costs and complexity, enhance device lifetime, reliability, and operational efficiency, thereby laying the foundation for future development of ultra-compact, high-performance monolithic integrated microdisplay chips[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAchieving efficient long-wavelength lasing in GaN-based QW materials presents a fundamental difficulty: increasing the emission wavelength requires raising the indium (In) composition in the InGaN quantum well active region to reduce the bandgap, which in turn escalates the growth challenges of the active region and introduces substantial lattice mismatch, leading to a significant drop in external quantum efficiency (EQE). Furthermore, for red lasers,the emission peak wavelength shift caused by the internal electric field is more severe than those caused in blue and green LDs. [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] These factors collectively degrade crystal quality, increase defect density, raise the laser threshold current, and impede improvements in efficiency, output power, and device lifetime.[\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe waveguide layers in laser structure serve to effectively confine generated laser photons within the active region, facilitating strong interaction with charge carriers (electrons and holes) to achieve efficient stimulated emission and laser output. They constitute one of the indispensable key structures enabling GaN-based lasers to operate with low threshold, high efficiency, and superior performance[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].In this paper, we shall investigate the influence of different parameters of InGaN waveguide layers, including In composition, layer thickness and structure, on the threshold current of lasers using the professional simulation software LASTIP.\u003c/p\u003e \u003cp\u003eLaser structure and simulation parameters\u003c/p\u003e \u003cp\u003eThe schematic diagram of the red QW laser structure employed in this study is shown in Fig.\u0026nbsp;1.The laser diode (LD) comprises a 1\u0026micro;m GaN substrate (Si: 1\u0026times;10\u0026sup2;⁴/m\u0026sup3;), a 1\u0026micro;m AlGaN cladding (Si: 1\u0026times;10\u0026sup2;⁴/m\u0026sup3;), a 0.12\u0026micro;m In\u003csub\u003ex\u003c/sub\u003eGa\u003csub\u003e1\u0026minus;x\u003c/sub\u003eN lower waveguide layer (Si: 1\u0026times;10\u0026sup2;⁴/m\u0026sup3;),an InGaN/GaN multiple quantum well (MQW) active region, a 0.1\u0026micro;m In\u003csub\u003ex\u003c/sub\u003eGa\u003csub\u003e1\u0026minus;x\u003c/sub\u003eN upper waveguide layer (Mg: 5\u0026times;10\u0026sup2;\u0026sup2;/m\u0026sup3;), a 0.005\u0026micro;m \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{A}{\\text{l}}_{0.03}\\text{G}{\\text{a}}_{0.97}\\text{N}\\)\u003c/span\u003e\u003c/span\u003e electron barrier layer (Mg: 1\u0026times;10\u0026sup2;⁵/m\u0026sup3;), 0.45\u0026micro;m AlGaN cladding layer (Mg: 1\u0026times;10\u0026sup2;⁵/m\u0026sup3;), 0.15\u0026micro;m p-GaN layer (Mg: 1\u0026times;10\u0026sup2;⁵/m\u0026sup3;), and 0.04\u0026micro;m highly doped p\u003csup\u003e++\u003c/sup\u003e-GaN contact layer (Mg: 1\u0026times;10\u0026sup2;⁶/m\u0026sup3;).Additionally, the LD device employs a rectangular waveguide structure with a ridge width and cavity length set at 3 \u0026micro;m and 600 \u0026micro;m respectively.\u003c/p\u003e \u003cp\u003eSoftware LASTIP is a specialized TCAD (Technology Computer-Aided Design) tool for simulating semiconductor lasers, primarily used to design and analyze the performance of semiconductor optoelectronic devices such as edge-emitting lasers and surface-emitting lasers. The software possesses robust multi-physics coupling simulation capabilities, enabling simultaneous handling of electrical, optical, and thermal simulations, as well as steady-state and transient characteristics[\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. It effectively models current-voltage characteristics and output power of laser diode devices. During calculations, both p-type and n-type electrodes are treated as ideal ohmic contacts, with the operating temperature set at 300 K. As defect charges and interface charges partially counteract the built-in polarization effect, interface charge values derived from the Fiorentini theoretical model typically exceed experimental values by 20%, 50%, or 80%[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Consequently, this study sets the polarization electric field to 25% of the theoretical value. In our simulations, the refractive indices of Al\u003csub\u003ex\u003c/sub\u003eGa\u003csub\u003e1\u0026minus;x\u003c/sub\u003eN and In\u003csub\u003ex\u003c/sub\u003eGa\u003csub\u003e1\u0026minus;x\u003c/sub\u003eN materials were calculated using the following formula[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:n（A{l}_{x}G{a}_{1-x}N）=\\left[n\\right(AlN)-n(GaN\\left)\\right]x+n\\left(GaN\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:n（I{n}_{x}G{a}_{1-x}N）=\\left[n\\right(InN)-n(GaN\\left)\\right]x+n\\left(GaN\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere the refractive indices for AlN, GaN, and InN are 2.247, 2.435, and 2.879 respectively.\u003c/p\u003e \u003cp\u003eFurthermore, we defined the absorption coefficient of different layers as a function of doping concentration, expressed as follows[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{\\text{a}}_{\\text{i}}=\\text{d}\\text{o}\\text{p}\\text{i}\\text{n}\\text{g}\\:\\text{c}\\text{o}\\text{n}\\text{c}\\text{e}\\text{n}\\text{t}\\text{r}\\text{a}\\text{t}\\text{i}\\text{o}\\text{n}\\left(\\text{c}{\\text{m}}^{-3}\\right)/(1\\ast\\:1{0}^{19}(\\text{c}{\\text{m}}^{-3})\\times\\:50(\\text{c}{\\text{m}}^{-1}\\left)\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_1 Schematic diagram of the laser structure\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eFirst, we employed LASTIP to calculate the lower threshold current of the P-I curve for the structure in Fig.\u0026nbsp;1 across different wavelengths. The lasing wavelength is dependent on the parameter selection of the QW active region. The threshold current represents the minimum injection current required for the laser to initiate stimulated emission (i.e., lasing). Only when the injection current exceeds this threshold, laser oscillation can occur, generating stimulated radiation through feedback within the optical resonator. This result in coherent laser emission is characterized by excellent directionality, high monochromaticity, and exceptional brightness. A lower threshold current indicates an easier lasing initiation, and normally also a higher energy conversion efficiency, alongside reduced operating temperatures and extended device lifetime. Figure\u0026nbsp;2 displays the P-I curves for the laser structure shown in Fig.\u0026nbsp;1 at different wavelengths under minimum threshold conditions. Overall, the laser's threshold current exhibits a continuous increase with increasing wavelength. Figure\u0026nbsp;2(a) and (b) depict the obtained P-I curves near 550 nm and 600 nm, respectively, with threshold currents of 34 mA and 36 mA near these two wavelengths. Compared to 550 nm, the threshold current at 600 nm increases by 2 mA.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_2(a): P-I curve near 550 nm; (b): P-I curve near 600 nm\u003c/p\u003e \u003cp\u003eSubsequently, we seek to grow high-quality long-wavelength lasers by changing the composition of waveguide layers. For this purpose, we have fixed the thickness of the upper waveguide at 100 nm and the thickness of the lower waveguide at 120 nm. Figure\u0026nbsp;3 shows the optimal In composition of the waveguide layers corresponding to obtaining the best threshold current at different wavelengths. A comparison reveals that the In composition required in the waveguide layers for reaching the lowest threshold current continuously increases with increasing wavelength, but it decreases when the wavelength increases beyond 616 nm. We then calculated the optical field distribution for lasers operating above 616 nm, between 616 nm and 656 nm, as shown in Fig.\u0026nbsp;3(b). These distribution curves revealed a shift in the optical field distribution, which should be the primary factor driving the required In composition decrease beyond 616 nm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_3 (a) In composition of the waveguide layers corresponding to the optimum threshold current, (b) The shifts of light field distribution curves obtained at different wavelengths, where the inset is an amplification of the top part of these curves.\u003c/p\u003e \u003cp\u003eOn the other hand, we consider that the thickness of the waveguide layers can also significantly influence the threshold current of long-wavelength lasers. We conducted a comparative study on the influence of thicknesses of both upper and lower waveguide layers. For this purpose, we fixed the In composition of both InGaN upper and lower waveguide layers to 0.078. First, we investigated the effect of varying upper and lower waveguide thicknesses on the optical characteristics of a 636 nm GaN-based laser. Figures\u0026nbsp;4(a) and (b) display the optical field distributions at a 150 mA current for varying thickness of upper or lower waveguide layers, respectively, where only one side's waveguide thickness is altered. The peak intensity on the right side ( around the active region and the upper waveguide) is markedly higher than that on the left side (around the lower waveguide region and the substrate side region,). It is noted that as the waveguide layer thickness increases, the peak intensity on the left side becomes markedly lower than that on the right. The slight displacement of the optical field in Fig.\u0026nbsp;4(b) arises because the position of the quantum well shifts as the lower waveguide thickens. These results indicate that an increased waveguide thickness, for both upper and lower waveguide layers, may enhance optical confinement, thereby suppressing field leakage and improving the optical performance of the 636 nm GaN-based laser.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_4 (a) Normalized Light field distribution when upper waveguide thickness changes (b) Normalzed light field distribution when lower waveguide thickness changes. In the figures, the right side peaks are located around the active region, the left side peaks are located in the lower waveguide region.\u003c/p\u003e \u003cp\u003eSubsequently, we investigated the relationship between output power and injection current (P-I curve) of a 636 nm GaN-based laser when varying only one-sided waveguide layer thickness, i.e. upper and lower waveguide layer thickness, as shown in Figs.\u0026nbsp;5(a) and 5(c), respectively. Figures\u0026nbsp;5(b) and 5(d) present the data of dependence of lasing threshold current on the thickness of upper and lower waveguide layer while the thickness of other waveguide is not changed. Upon increasing the injection current to threshold current, the devices start lasing. After lasing, the laser output power exhibit a sharp rise. It is found that as the injection current continues to increase, the output power of lasers is significantly improved with increasing waveguide thickness, as shown in Fig.\u0026nbsp;5 (a) and (c).As the waveguide layer thickness increases, the threshold injection current for laser operation decreases as shown in Fig.\u0026nbsp;5(b) and (d). However, it is noted ,as shown in the Fig.\u0026nbsp;5 ( d ) when the lower waveguide thickness increases up to beyond 300 nm, the threshold current begins to increase slightly. To find its reason, we calculated the optical confinement factor (OCF)and internal absorption loss ༈IAL༉for lasers in which lower waveguide layer thickness changes in the range between 260 nm to 340 nm. The results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. It is found that when the lower waveguide layer becomes much thicker, the center of optical field distribution curve shifts downward. This reduces the proportion of overlapping field energy in the active region, thereby decreasing the optical confinement factor (Γ). At the same time, the internal absorption loss exhibits a trend of gradually increases. As a whole, the threshold current shows a slight increase due to the combined effects of these two factors. In summary, if the waveguide thickness is not too large, increasing the waveguide layer thickness effectively reduces the threshold current, thereby significantly improving the electrical performance of InGaN-based red light-emitting laser diodes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_5 (a) P-I curves corresponding to different thicknesses of upper waveguide layer; (b) The data points for threshold current under varying upper waveguide thicknesses (*) for a 636 nm laser structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_5 (c) P-I curves corresponding to different lower waveguide thicknesses; (d) Data points of threshold currents for different thicknesses(*) of lower waveguide layer\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOptical confinement factor and internal absorption loss corresponding to different lower waveguide layer thicknesses\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLWG Thickness (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e260\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e280\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e320\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e340\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOCF(10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.559\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.573\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.580\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.585\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.586\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIAL(10\u003csup\u003e4\u003c/sup\u003e/cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.136\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.139\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo further investigate the influence of waveguide layer structure on laser performances, we propose a stepped waveguide structure. A 636 nm laser was selected as a representative example. In the stepped laser structure, the thickness of upper waveguide layer is fixed to be 100 nm. Both upper and lower waveguide layers are divided into two parts with equal thickness, but with different In compositions,(the In component near the active region is 0.078, while the In component away from the active region is 0.048.) Then the P-I curves have been calculate and shown in Fig.\u0026nbsp;6(a) where the total thickness of lower waveguide layer increases from 120 nm to 260 nm. Figure\u0026nbsp;6(b) shows the corresponding data points of the threshold current of these laser structures. Figure\u0026nbsp;6(c) displays the corresponding optical field distributions. The obtained results indicate that, at equivalent thicknesses, the threshold current behavior of the lasers with stepped waveguide layers significantly outperforms that with single-layered waveguide structure. It can be seen from a comparison between the curve shown in Fig.\u0026nbsp;6 (b) with the curve shown in Fig.\u0026nbsp;5 (d), the threshold current value is lower for stepped structure laser. In fact ,in both cases the threshold current continues to decrease as the thickness difference increases. Furthermore, even with stepped waveguide structure part of In composition is reduced from 0.78 to 0.48, with a lower total In composition in the lower waveguide layer, the lasers with stepped waveguide still exhibit a better optical confinement and a reduced light leakage compared to lasers with single-layer waveguide structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure_6 (a) P-I curves of 636 nm lasers with stepped waveguides of different total thicknesses of er waveguide layer. Threshold currents for lasers with stepped waveguides of corresponding thicknesses, (c)Normalized Light field Distribution in Stepped Waveguides of Different lower waveguide thicknesses\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we designed and calculated the influences of InGaN waveguide layers In composition on laser performances at different wavelengths using LASTIP simulation software.The study revealed that, in overall, as the laser wavelength increases, the In composition in the waveguide layer required for the best threshold current continuously rises, and the threshold current also gradually increases. We investigated the effects of varying thickness and waveguide layer structure on the threshold current of 636 nm red lasers. The results show that with a lower average. In content, stepped waveguide layers of the same total thickness actually provide better optical field confinement and lower threshold current.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDisclosures.\u003c/h2\u003e \u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eZ.G. and M.Z. and D.Z. conceived the study. Z.G. designed the experiments and performed the measurements. Z.G. and J.S. developed the analytical software. Z.G. and Y.W. performed the data analysis. X.W. and X.Z. contributed to data collection and validation. Z.G. wrote the original draft. Z.G. and M.Z. and D.Z. reviewed and edited the manuscript. M.Z. supervised the project and acquired funding. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBen, Y., et al.: Different influence of InGaN lower waveguide layer on the performance of GaN-based violet and ultraviolet laser diodes. Superlattices Microstruct. \u003cb\u003e133\u003c/b\u003e, 8 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, J.: When group-III nitrides go infrared: New properties and perspectives. J. Appl. Phys. \u003cb\u003e106\u003c/b\u003e, 28 (2009)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWong, M., et al.: High efficiency of III-nitride micro-light-emitting diodes by sidewall passivation using atomic layer deposition. Opt. Express. \u003cb\u003e26\u003c/b\u003e, 21324\u0026ndash;21331 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang, X., et al.: Study on the performance of InGaN-based green LED by designing different preparing layers. Opt. Mater. \u003cb\u003e89\u003c/b\u003e, 505\u0026ndash;511 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, P., et al.: Very high external quantum efficiency and wall-plug efficiency 527 nm InGaN green LEDs by MOCVD. Opt. Express. \u003cb\u003e26\u003c/b\u003e, 33108\u0026ndash;33115 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLv, Q., et al.: Realization of Highly Efficient InGaN Green LEDs with Sandwich-like Multiple Quantum Well Structure: Role of Enhanced Interwell Carrier Transport. ACS Photonics. \u003cb\u003e6\u003c/b\u003e, 130\u0026ndash;138 (2019)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBi, Z., et al.: In: Jiang, H., Lin, J. (eds.) From nanoLEDs to the realization of RGB-emitting microLEDs, in \u003cem\u003eMicro Leds\u003c/em\u003e, pp. 223\u0026ndash;251. Elsevier Academic Press Inc, San Diego (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHsiang, E., et al.: Prospects and challenges of mini-LED, OLED, and micro-LED displays. J. Soc. Inf. Disp. \u003cb\u003e29\u003c/b\u003e, 446\u0026ndash;465 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIida, D., et al.: Demonstration of low forward voltage InGaN-based red LEDs. Appl. Phys. Express. \u003cb\u003e13\u003c/b\u003e, 4 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIida, D., et al.: 633-nm InGaN-based red LEDs grown on thick underlying GaN layers with reduced in-plane residual stress. Appl. Phys. Lett. \u003cb\u003e116\u003c/b\u003e, 5 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, S., et al.: Efficient emission of InGaN-based light-emitting diodes: toward orange and red. Photonics Res. \u003cb\u003e8\u003c/b\u003e, 1671\u0026ndash;1675 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoukitu, A., et al.: Thermodynamic analysis of the MOVPE growth of InxGa1-xN. J. Cryst. Growth. \u003cb\u003e170\u003c/b\u003e, 306\u0026ndash;311 (1997)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYamashita, Y., et al.: Control of emission wavelength of GaInN single quantum well, light emitting diodes grown hy metalorganic chemical vapor deposition in a split-flow reactor, Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Brief Commun. Rev. Pap. 42, 4197\u0026ndash;4202 (2003)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShimizu, M., et al.: Metalorganic vapor phase epitaxy of thick InGaN on sapphire substrate, Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Brief Commun. Rev. Pap. 36, 3381\u0026ndash;3384 (1997)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHolec, D., et al.: Critical thickness calculations for InGaN/GaN. J. Cryst. Growth. \u003cb\u003e303\u003c/b\u003e, 314\u0026ndash;317 (2007)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, X., et al.: The influence of material quality of lower InGaN waveguide layer on the performance of GaN-based laser diodes. Appl. Surf. Sci. \u003cb\u003e570\u003c/b\u003e, 6 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, W., et al.: Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers. Chin. Phys. B. \u003cb\u003e31\u003c/b\u003e, 6 (2022)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXing, Y., et al.: Suppression of electron and hole overflow in GaN-based near-ultraviolet laser diodes. Chin. Phys. B. \u003cb\u003e27\u003c/b\u003e, 6 (2018)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHou, Y., et al.: Characteristics of InGaN-based green laser diodes with additional InGaN hole reservoir layer. Vacuum. \u003cb\u003e186\u003c/b\u003e, 7 (2021)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiang, F., et al.: Output light power of InGaN-based violet laser diodes improved by using a u-InGaN/GaN/AlGaN multiple upper waveguide. Chin. Phys. B. \u003cb\u003e26\u003c/b\u003e, 5 (2017)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChichibu, S., et al.: Effective band gap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures. Appl. Phys. Lett. \u003cb\u003e73\u003c/b\u003e, 2006\u0026ndash;2008 (1998)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, H., et al.: Measurement of polarization charge and conduction-band offset at InxGa1-xN/GaN heterojunction interfaces. Appl. Phys. Lett. \u003cb\u003e84\u003c/b\u003e, 4644\u0026ndash;4646 (2004)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRenner, F., et al.: Quantitative analysis of the polarization fields and absorption changes in InGaN/GaN quantum wells with electroabsorption spectroscopy. Appl. Phys. Lett. \u003cb\u003e81\u003c/b\u003e, 490\u0026ndash;492 (2002)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, L., et al.: Confinement factor and absorption loss of AlInGaN based laser diodes emitting from ultraviolet to green. J. Appl. Phys. \u003cb\u003e105\u003c/b\u003e, 8 (2009)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang, C., et al.: Optical waveguide simulations for the optimization of InGaN-based green laser diodes. J. Appl. Phys. \u003cb\u003e107\u003c/b\u003e, 7 (2010)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"GaN-based red lasers, Waveguide layers, Optical field, Threshold current","lastPublishedDoi":"10.21203/rs.3.rs-9299993/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9299993/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe threshold current of GaN-based quantum well(QW) red lasers is modulated by modifying the In composition of InGaN waveguide layers and adjusting the thickness and structure of waveguide layers. Theoretical analysis based on LASTIP calculations reveals that the In composition for achieving the best threshold current increases initially with increasing laser wavelength, but when the wavelength reaches up to a value, it turns to decrease. Additionally, for the 636 nm GaN-based red laser, the threshold current decreases with increasing waveguide layer thickness. Furthermore, the threshold current for lasers with a stepped waveguide structure of the same total thickness is lower than that for a single-layer waveguide. This work provides a new approach for structural optimization of GaN-based QW red lasers.\u003c/p\u003e","manuscriptTitle":"Optimized Design of the Waveguide Layers for GaN-Based QW Red Lasers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-20 15:28:38","doi":"10.21203/rs.3.rs-9299993/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-03T12:52:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-03T12:14:44+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-03T11:54:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2026-04-02T07:52:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"25483934-69ba-48c2-a168-9c3e7a3e2882","owner":[],"postedDate":"April 20th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-17T03:23:21+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-20 15:28:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9299993","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9299993","identity":"rs-9299993","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}