m-Plane GaN Split-Well Direct-phonon Terahertz Quantum Cascade Laser

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The design employs the split-well direct-phonon (SWDP) scheme and is analyzed using the Non-equilibrium Green’s Function (NEGF) approach. The proposed design successfully addresses key limitations identified in previous studies, particularly the challenge of balancing high gain with lower current density thereby mitigating the risk of thermal damage. By introducing a thin barrier within the wider well, we achieved a substantial reduction in doping density leading to lower current density while preserving strong gain performance. Our simulations show that the m-plane SWDP GaN-based QCL can achieve lasing at ~ 8.7 THz, with 14% Al in the barrier and 7% Al in the intra-well barrier, with maximum operating temperature (Tmax) up to ~ 280 K. This lasing frequency exceeds the typical limits of GaAs-based THz QCLs, demonstrating the potential of GaN-based designs for extended frequency coverage and high-temperature operation. Physical sciences/Materials science Physical sciences/Optics and photonics Physical sciences/Physics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Terahertz (THz) radiation is non-ionizing and exhibits unique interactions with a wide variety of materials, making it an attractive tool for numerous applications. In the field of spectroscopy, THz waves can probe low-energy excitations such as phonons, molecular rotations, and hydrogen bonding, enabling chemical identification and structural analysis of complex compounds 1 . In imaging, THz technology is increasingly used for security screening 2 , non-destructive testing 3 , and biomedical diagnostics 4 , owing to its ability to penetrate many non-metallic materials while revealing contrast invisible in other spectral ranges. Beyond sensing and imaging, the THz regime is emerging as a candidate for next-generation wireless communications 5 , offering ultra-broad bandwidths that could support data rates far exceeding current 5G capabilities 6 . Additionally, THz sources and detectors are critical components in quantum optics and condensed matter research, where they enable coherent control of quantum states and investigation of ultrafast carrier dynamics 7 . Despite these promising applications, the development of compact, efficient, and room temperature THz devices remains a key challenge. This has spurred intense efforts to design and engineer novel electronic, optoelectronic, and photonic systems such as THz quantum cascade lasers (THz QCLs). Although THz QCLs offer many advantages, they have not yet matured into commercially THz sources. One of the main limitations is their reliance on cryogenic cooling, which confines their use to laboratory environments and prevents the development of compact, portable THz source. As a result, enhancing the maximum operating temperature (T max ) continues to be a central challenge in the field. Progress in the field has led to the demonstration of a compact THz QCL system operating at temperatures up to ~ 250 K 8 . with further improvements pushing the performance to a record T max of ~ 261 K using GaAs/AlGaAs heterostructures 9 . However, these successes still fall short of overcoming the key barrier and achieving room-temperature operation of THz QCLs remains an unresolved challenge. GaAs-based THz QCLs, which currently dominate THz device development 10 11 12 13 14 , are confined to a relatively narrow emission range between 1.2-6 THz 15 16 17 . While theoretical studies suggest that operation could extend up to 6.6 THz 18 , achieving practical lasing beyond 6 THz remains highly challenging. Consequently, the 6–12 THz frequency window is still largely unexplored 19 20 . This spectral gap significantly limits the utility of THz-QCLs in applications such as material identification and analysis 21 , where many substances, including water, proteins, semiconductors, and pigments, exhibit strong absorption features in the 5–25 THz range 22 23 . The primary reason GaAs-based devices cannot access this region is the presence of the Reststrahlen band between 8–9 THz. In contrast, III-nitride semiconductors like GaN, AlGaN, and AlN offer a pathway to overcome this limitation. Their high longitudinal optical (LO) phonon energies (> 22 THz) push the Reststrahlen band out to 17–22 THz, leaving the 5–12 THz region accessible for laser operation 24 25 . Additionally, GaN, possesses a significantly higher LO phonon energy of ~ 90 meV, compared to ~ 36 meV in GaAs. These materials are better suited for high-temperature operation, as their large phonon energies reduce losses from thermally activated scattering and carrier backfilling 26 , key factors that limit performance in GaAs systems 27 28 29 . Here, we choose m-plane nonpolar GaN quantum wells over conventional c-plane structures, as they eliminate polarization-induced electric fields. The c-plane orientation introduces strong polarization fields, resulting in a sharply tilted conduction band with a trapezoidal-like profile. This distortion complicates the alignment of electronic subbands required for efficient QCL operation 30 31 32 . The m-plane structure, being free from such polarization effects, offers a flat conduction band similar to that of GaAs-based THz QCLs. This similarity simplifies the design process and enhances control over electronic transitions within the structure 33 34 35 36 37 38 39 . Methods Within this study, we have theoretically analyzed a SWDP m-plane GaN/ Al0.14Ga0.86N THz-QCL structure. Nitride structures on nonpolar planes suppress polarization fields but suffer from growth-related challenges, including high defect densities, anisotropy, cracking, hillocks, and basal-plane stacking faults 40 . To address these issues, we optimized the maximum aluminum content in AlₓGa₁₋ₓN barriers to x = 14%, which represents a trade-off between optimal QCL design and the suppression of defects, dislocations, and surface degradation. This composition provides sufficient carrier confinement while minimizing lattice-mismatch-induced defects, dislocations, and surface degradation. The primary motivation for employing the SWDP scheme lies in its inherent structural and transport advantages: it enables direct depopulation of the lower laser level (LLL) into the injector level within the same well, removing the need for an additional extraction level 11 35 41 8 . In addition, The SWDP scheme mitigates the major drawback of traditional two-well (TW) QCLs, where the high electric fields across short modules lead to significant carrier leakage 10 42 34 . Our primary goal in applying the SWDP scheme to the GaN material system was to design a practical structure and to avoid the limitations previously observed in our work 19 . In our previous studies, we achieved a significant increase in doping levels while still observing an improvement in gain. The driving force behind this enhanced doping lies in the considerable energy difference (~ 95 meV) between the LLL and the injector level within our GaN-based structure. Importantly, this energy difference plays a critical role in suppressing the thermal backfilling effect, allowing us to increase the doping density significantly within our structure. By mitigating thermal backfilling, we were able to raise the doping levels considerably, leading to an increase in gain. However, although increasing the doping density value emerge as a key factor in the improvement of the gain performance. The high doping can result in high current, and this high current could eventually cause the device to burn out. Our recent work 43 proposes a more practical alternative to the previously suggested TW GaN THz QCL 19 , achieving significantly lower operating currents that reduce the risk of thermal damage and improve the prospects for experimental realization. The inclusion of an additional barrier helps to suppress carrier leakage into the continuum and excited states however, while the current is reduced, it remains relatively high, and the added barrier makes energy level alignment more challenging. A central achievement of our work lies in the successful reduction of doping density, which leads to a lower current density while still maintaining the desired gain performance. By the addition of a thin barrier within the wider well, we manage to maintain the gain performance of our previous studies with significantly lower doping density level and as a result to reduce the current density. In addition, employing the SWDP scheme simplifies the alignment of the electronic levels. To evaluate the carrier behavior and optical gain in the SWDP design, we performed a full-scale theoretical study using self-consistent simulations based on the non-equilibrium Green’s function (NEGF) formalism. This framework enables a quantum-level assessment of transport phenomena and gain characteristics by capturing the effects of quantum coherence and scattering processes 44 45 46 . Our model includes both elastic and inelastic scattering channels that critically influence carrier dynamics. These involve ionized impurity scattering (IIS), alloy disorder, electron-electron (e-e) interactions, and interface roughness (IFR), alongside energy dissipating interactions with both optical and acoustic phonons. The interface morphology was modeled using a roughness amplitude of 1 Å and a correlation length of 80 Å, these parameter values follow commonly established conventions in the field and correspond roughly to the roughness of a single atomic layer at the interface 30 47 37 48 . A key aspect of our simulation is the inclusion of excited states. Ignoring these states can lead to an overly optimistic estimation of gain and an incomplete understanding of leakage paths 49 28 . Including these states enhances the predictive reliability of our model and demonstrates the practical viability of fabricating such a device. Results and discussions Figure 1 represents the conduction band diagram of an m-plane GaN THz QCL employing SWDP scheme. The structure is based on three subbands in each module. The layer sequence within one period, starting from the injection barrier, is as follows: 15 /25/ 10 /28.5/ 10 /27.5 Å, with the barriers indicated in bold font. A sheet doping density of ~ 3×10 10 cm − 2 is introduced in each period. The doped region is 15 Å wide, placed within the widest well, symmetrically on both sides of the split section. This configuration facilitates efficient electron injection. The injection barrier contains 14% Al, a value deliberately chosen to balance sufficient carrier confinement with material quality. A higher Al composition can introduce strain-induced defects, such as dislocations, that degrade crystal quality and device performance 40 . The intrawell barrier, with a lower Al content of 7%, is inserted inside the wider well. This barrier has the same thickness as the injection barrier but reduced height, which facilitates resonant tunneling in addition to LO-phonon–assisted depopulation, thereby improving the efficiency of carrier extraction from the lower laser level. In the conduction band diagram, the ULL (level 2) is aligned with the injector level of the preceding module (level 1), enabling resonant tunneling. This strong coupling arise from the significantly stronger LO-phonon interaction in GaN, up to 16 times higher than in GaAs 19 50 . The radiative transition occurs between level 2 (ULL) and level 3 (LLL). Electrons are then relaxed into the injector level (level 1′), and subsequently injected into the next period, continuing the lasing cycle. In this structure, the LLL (level 3) and the injector level of the next module (level 1′) are aligned to form a direct phonon scattering pathway, similar to the TW scheme 19 . The energy difference between the LLL and the injector level is ̴ 60 meV. The depopulation of the LLL is achieved via the combination of LO-phonon scattering and resonant tunneling to the next module. For further performance optimization, NEGF simulations were employed to model carrier transport and gain under room-temperature conditions. Our optimization process included a detailed study of the doping level, as illustrated in Fig. 2 , where we present the simulated gain spectra at various doping densities. We began our investigation with a doping density of ̴ 3×10¹¹ cm⁻², which was previously identified as the optimal value in our earlier works 1 9 43 , yielding the highest peak gain. This doping density value is about one order of magnitude higher than the typical doping densities used in conventional GaAs-based THz QCLs. The motivation behind this study was to explore whether lower doping densities, comparable to those used in GaAs devices, could reduce the high current densities typically associated with highly doped structures while still maintaining sufficient gain. Contrary to the former assumption that increasing the doping density leads to higher gain, our results reveal the opposite trend. In our design, we observe a reduction in optical gain with increasing doping density, a trend primarily attributed to the relatively small energy separation between the LLL and the injector level (~ 60 meV). This limited spacing enhances the susceptibility of the structure to thermal backfilling, particularly at elevated doping levels, which in turn degrades population inversion and reduces gain 5 1 . To address this, we implemented a barrier with reduced aluminum content (7% Al) inside the wider well, serving as a thin intrawell barrier. While its thickness matches that of the injection barrier, the lower Al concentration reduces the barrier height, thereby increasing the probability of resonant tunneling from the LLL to the injector level of the next module, in addition to LO-phonon–assisted depopulation. This combined mechanism enables faster and more efficient depletion of the LLL, which helps counteract the limitations imposed by thermal backfilling and supports gain performance with lower doping densities. As shown in the plot, we observe that as the doping density decreases, the peak gain increases. At low temperature, the highest peak gain was achieved with a doping density value of ̴ 6×10 10 cm −2 . However, the highest operating temperature was obtained using a lower doping density value of ̴ 3×10 10 cm −2 . Since the primary goal of our work is to achieve room-temperature laser emission, we selected a doping density value of 3×10 10 cm⁻² for our final simulations and design optimization. Figure 3 represents the current density as a function of voltage in different temperatures in the TW and Resonant Phonon (RP) and SWDP schemes. As can be seen from the figure, the current density reduced by almost a factor of two in the RP scheme in comparison to the TW scheme and by factor of four in the SWDP scheme in comparison to the TW scheme. This marked reduction significantly enhances the feasibility of realizing a functional experimental device and lowers the likelihood of thermal damage. While the operating current remains relatively high, the SWDP design nonetheless provides the greatest potential for successful experimental implementation. Figure 4 represents the optical gain versus photon frequency in various temperatures. These simulations include excited state contributions, which are essential for capturing realistic carrier dynamics, particularly at elevated temperatures. The peak of the curve corresponds to a photon frequency of ~ 8.7 THz. As the temperature increases, the gain remains relatively stable up to approximately 200 K, beyond which a clear decline is observed. Our simulation shows that at 10 K and in 280 K the gain values are ~ 42 cm − 1 and ~ 17 cm − 1 respectively which is above the estimated losses for double metal 52 very close to room temperature and shows the feasibility for high temperature operation. Our simulation includes all the scattering mechanisms and the excited states in order to show the feasibility of a practical device. To gain deeper insight into the physical processes limiting the performance of the device, we conducted a series of simulations in which each scattering mechanism was selectively eliminated, one at a time, while keeping all other scattering processes unchanged. This approach allowed us to isolate and assess the individual impact of each mechanism on optical gain. Figure 5 shows the simulated optical gain as a function of photon frequency for each case. The simulations were carried out at a temperature of 10 K and a bias voltage of 95 mV/module. Our analysis underscores that the scattering mechanisms most strongly impacting the gain performance are primarily associated with IFR scattering. Among all the mechanisms examined, the removal of IFR scattering resulted in the most significant increase in peak gain. These findings highlight the critical importance of interface quality and suggest that further improvements in material growth and interface control could directly translate into enhanced device performance. This is particularly relevant for GaN-based structures, where growth technology is still under development and not as refined as the long-established GaAs growth methods. As a result, MBE growth in GaN systems tends to exhibit greater IFR. The elevated IFR in GaN/AlGaN heterostructures thus presents a significant challenge, directly impacting the optical gain. In addition, IIS and e–e interactions also contribute to gain suppression, though to a lesser extent. The influence of alloy disorder was found to be relatively minor under the simulated conditions. The simulation results are consistent with the fact that we use a relatively low doping density, which reduces the impact of e–e scattering and IIS, whereas IFR emerges as the dominant limiting mechanism due to the inherent challenges in achieving high-quality interfaces in GaN heterostructures. Conclusions In summary, we have presented a theoretical investigation of a GaN-based THz QCL structure utilizing the SWDP scheme along the non-polar m-plane orientation. Using a self-consistent NEGF approach, we performed detailed simulations of carrier transport and optical gain, taking into account a full range of scattering mechanisms. The structure demonstrates promising performance, achieving a peak gain of ~ 43 cm⁻¹ at 10 K with the gain remaining above the estimated losses even at the elevated temperature of ∼ 280 K, with an emission frequency ∼8.7 THz, a spectral range that lies beyond what has been realized with GaAs-based THz QCLs. The proposed structure effectively overcomes several limitations identified in previous studies, most notably the trade-off between high gain and low current density, which is critical for reducing the risk of thermal degradation. By incorporating a thin barrier within the wide well, we achieved a significant reduction in doping density, thereby lowering the current density while preserving robust gain performance. Furthermore, our scattering analysis reveals that IFR is the dominant mechanism limiting gain, a result that aligns with the known difficulties in achieving high-quality interfaces in GaN/AlGaN systems due to limitations in current epitaxial growth techniques. The use of a low doping level in our structure also reduces the impact of e-e scattering. These findings demonstrate that the SWDP-based GaN THz QCL design offers a practical route toward efficient, high-temperature THz laser sources, and lays the groundwork for future experimental realization. Declarations Acknowledgements The authors would like to acknowledge the Israel Innovation Authority for its grant provided through the Academic Applied Research Program, the Israel Ministry of Science and Technology for their grant for proposal 0007465, and the Israel Science Foundation for its grant (ISF 1755/23). Author contributions All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission. Shiran Levy performed the simulations, analyzed the data, wrote the manuscript text, and contributed to the discussion of the results. Nathalie Lander Gower supported the data analysis and the writing process. Silvia Piperno managed project administration, supported the writing process. Gad Bahir, supported the research and writing processes, funding acquisition. Asaf Albo led the conceptualization, funding acquisition, investigation, project management, supervision, and the writing and editing of the manuscript. Funding This work was supported and funded by the Israel Innovation Authority, the Israel Ministry of Science and Technology and the Israel Science Foundation. Competing interests The authors declare no conflicts of interest regarding this article. Data availability The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request. References McIntosh, A. I., Yang, B., Goldup, S. M., Watkinson, M. & Donnan, R. S. Terahertz spectroscopy: a powerful new tool for the chemical sciences? Chem Soc Rev 41, 2072–2082 (2012). Federici, J. F. et al. THz imaging and sensing for security applications—explosives, weapons and drugs. Semicond. Sci. Technol. 20, S266 (2005). Nsengiyumva, W. et al. Sensing and Nondestructive Testing Applications of Terahertz Spectroscopy and Imaging Systems: State-of-the-Art and State-of-the-Practice. IEEE Trans. Instrum. Meas. 72, 1–83 (2023). Gong, A. et al. 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Albo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYJCCDwwFBxj4QayEAuJ0MM5gMDjAINkA0mJAihYgAgJitPD3H37Y8MPgjpzx+dWJHx4YMMjzix3Ar0XiRpphY4/BM2OzG283SwAdZjhzdgIBa24wmD/gMTicuO3G2Q0gLQkGtwlokT9//GPjH6CWzTPObv5BlBaDAzmGzSBbNvD3biPOFsMbOYXNMkC/SNzg3WaRYCBB2C9y549vbHxTcUeOv//s5ps/Kmzk+aUJaEEACbBKCWKVgwD/AVJUj4JRMApGwUgCADwsS6UAxpwfAAAAAElFTkSuQmCC","orcid":"","institution":"Ariel University","correspondingAuthor":true,"prefix":"","firstName":"Asaf","middleName":"","lastName":"Albo","suffix":""}],"badges":[],"createdAt":"2025-09-25 10:23:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7711779/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7711779/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":94176763,"identity":"81852ce3-8b91-4325-8f5c-6c6245c68f48","added_by":"auto","created_at":"2025-10-23 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08:37:11","extension":"html","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":103556,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/eacf2b828319f58a079e6162.html"},{"id":94176756,"identity":"290c6f4d-698f-4379-b6df-a07a92ea5909","added_by":"auto","created_at":"2025-10-23 08:37:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":42515,"visible":true,"origin":"","legend":"\u003cp\u003eBand diagram of three periods of the SWDP GaN THz-QCLs with injection and radiative Al\u003csub\u003e0.14\u003c/sub\u003eGa\u003csub\u003e0.86\u003c/sub\u003eN barriers, and Al\u003csub\u003e0.07\u003c/sub\u003eGa\u003csub\u003e0.93\u003c/sub\u003eN intarwell barriers, at 10 K and 95 mV, with doping level of ~3×1010 cm-2. barrier/well width :\u003cstrong\u003e15\u003c/strong\u003e/25/\u003cstrong\u003e10\u003c/strong\u003e/28.5/\u003cstrong\u003e10\u003c/strong\u003e/27.5 Å.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/e27ccf82dfc7998f1bf8cb84.png"},{"id":94176757,"identity":"45735e0f-6363-48e3-aba7-6abe1fd43f4f","added_by":"auto","created_at":"2025-10-23 08:37:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":40299,"visible":true,"origin":"","legend":"\u003cp\u003eOptical gain as a function of photon frequency at a bias voltage of 95 mV/module at 10 K for different doping densities values.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/201108fafe4759e0eb8f9fd1.png"},{"id":94177684,"identity":"5528ea8a-34c0-492c-a19e-7d07a178bc1f","added_by":"auto","created_at":"2025-10-23 08:45:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":35855,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent density as a function of bias voltage at different temperatures. For TW and RP and SWDP GaN based THz QCLs.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/ec5d486b6329fe60f5a4b12c.png"},{"id":94176759,"identity":"57c45c4c-a7f8-4a20-8ad8-8190204d4902","added_by":"auto","created_at":"2025-10-23 08:37:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":33731,"visible":true,"origin":"","legend":"\u003cp\u003eOptical gain as a function of photon frequency at a bias voltage of 95 mV/module at different temperatures, excited states included. Estimated losses line of 15 cm\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/a341762b7e4b7385cdf038a8.png"},{"id":94176760,"identity":"4535e368-e855-41cb-a4b2-b2348d0d2ee6","added_by":"auto","created_at":"2025-10-23 08:37:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":38685,"visible":true,"origin":"","legend":"\u003cp\u003eThe contribution of the different scattering mechanisms to the optical gain at temperature of 10 K and bias voltage of 95 mV/module.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/574b112dda8840949b6193d6.png"},{"id":94178816,"identity":"67c00ea7-aee1-4f8a-953e-8d27f364a255","added_by":"auto","created_at":"2025-10-23 09:01:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":623019,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7711779/v1/8b71ca9c-6495-4df0-8f70-c6714663ee5c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"m-Plane GaN Split-Well Direct-phonon Terahertz Quantum Cascade Laser","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTerahertz (THz) radiation is non-ionizing and exhibits unique interactions with a wide variety of materials, making it an attractive tool for numerous applications. In the field of spectroscopy, THz waves can probe low-energy excitations such as phonons, molecular rotations, and hydrogen bonding, enabling chemical identification and structural analysis of complex compounds\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. In imaging, THz technology is increasingly used for security screening\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, non-destructive testing\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, and biomedical diagnostics\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, owing to its ability to penetrate many non-metallic materials while revealing contrast invisible in other spectral ranges. Beyond sensing and imaging, the THz regime is emerging as a candidate for next-generation wireless communications\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, offering ultra-broad bandwidths that could support data rates far exceeding current 5G capabilities\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Additionally, THz sources and detectors are critical components in quantum optics and condensed matter research, where they enable coherent control of quantum states and investigation of ultrafast carrier dynamics\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eDespite these promising applications, the development of compact, efficient, and room temperature THz devices remains a key challenge. This has spurred intense efforts to design and engineer novel electronic, optoelectronic, and photonic systems such as THz quantum cascade lasers (THz QCLs).\u003c/p\u003e\u003cp\u003eAlthough THz QCLs offer many advantages, they have not yet matured into commercially THz sources. One of the main limitations is their reliance on cryogenic cooling, which confines their use to laboratory environments and prevents the development of compact, portable THz source. As a result, enhancing the maximum operating temperature (T\u003csub\u003emax\u003c/sub\u003e) continues to be a central challenge in the field.\u003c/p\u003e\u003cp\u003eProgress in the field has led to the demonstration of a compact THz QCL system operating at temperatures up to ~\u0026thinsp;250 K\u003csup\u003e8\u003c/sup\u003e. with further improvements pushing the performance to a record T\u003csub\u003emax\u003c/sub\u003e of ~\u0026thinsp;261 K using GaAs/AlGaAs heterostructures\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. However, these successes still fall short of overcoming the key barrier and achieving room-temperature operation of THz QCLs remains an unresolved challenge.\u003c/p\u003e\u003cp\u003eGaAs-based THz QCLs, which currently dominate THz device development\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, are confined to a relatively narrow emission range between 1.2-6 THz\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. While theoretical studies suggest that operation could extend up to 6.6 THz\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, achieving practical lasing beyond 6 THz remains highly challenging. Consequently, the 6\u0026ndash;12 THz frequency window is still largely unexplored\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. This spectral gap significantly limits the utility of THz-QCLs in applications such as material identification and analysis\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, where many substances, including water, proteins, semiconductors, and pigments, exhibit strong absorption features in the 5\u0026ndash;25 THz range\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe primary reason GaAs-based devices cannot access this region is the presence of the Reststrahlen band between 8\u0026ndash;9 THz. In contrast, III-nitride semiconductors like GaN, AlGaN, and AlN offer a pathway to overcome this limitation. Their high longitudinal optical (LO) phonon energies (\u0026gt;\u0026thinsp;22 THz) push the Reststrahlen band out to 17\u0026ndash;22 THz, leaving the 5\u0026ndash;12 THz region accessible for laser operation\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Additionally, GaN, possesses a significantly higher LO phonon energy of ~\u0026thinsp;90 meV, compared to ~\u0026thinsp;36 meV in GaAs. These materials are better suited for high-temperature operation, as their large phonon energies reduce losses from thermally activated scattering and carrier backfilling\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, key factors that limit performance in GaAs systems\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eHere, we choose m-plane nonpolar GaN quantum wells over conventional c-plane structures, as they eliminate polarization-induced electric fields. The c-plane orientation introduces strong polarization fields, resulting in a sharply tilted conduction band with a trapezoidal-like profile. This distortion complicates the alignment of electronic subbands required for efficient QCL operation\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The m-plane structure, being free from such polarization effects, offers a flat conduction band similar to that of GaAs-based THz QCLs. This similarity simplifies the design process and enhances control over electronic transitions within the structure\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eWithin this study, we have theoretically analyzed a SWDP m-plane GaN/ Al0.14Ga0.86N THz-QCL structure. Nitride structures on nonpolar planes suppress polarization fields but suffer from growth-related challenges, including high defect densities, anisotropy, cracking, hillocks, and basal-plane stacking faults\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. To address these issues, we optimized the maximum aluminum content in AlₓGa₁₋ₓN barriers to x = 14%, which represents a trade-off between optimal QCL design and the suppression of defects, dislocations, and surface degradation. This composition provides sufficient carrier confinement while minimizing lattice-mismatch-induced defects, dislocations, and surface degradation.\u003c/p\u003e\u003cp\u003eThe primary motivation for employing the SWDP scheme lies in its inherent structural and transport advantages: it enables direct depopulation of the lower laser level (LLL) into the injector level within the same well, removing the need for an additional extraction level\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. In addition, The SWDP scheme mitigates the major drawback of traditional two-well (TW) QCLs, where the high electric fields across short modules lead to significant carrier leakage\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eOur primary goal in applying the SWDP scheme to the GaN material system was to design a practical structure and to avoid the limitations previously observed in our work\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. In our previous studies, we achieved a significant increase in doping levels while still observing an improvement in gain. The driving force behind this enhanced doping lies in the considerable energy difference (~ 95 meV) between the LLL and the injector level within our GaN-based structure. Importantly, this energy difference plays a critical role in suppressing the thermal backfilling effect, allowing us to increase the doping density significantly within our structure. By mitigating thermal backfilling, we were able to raise the doping levels considerably, leading to an increase in gain. However, although increasing the doping density value emerge as a key factor in the improvement of the gain performance. The high doping can result in high current, and this high current could eventually cause the device to burn out. Our recent work\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e proposes a more practical alternative to the previously suggested TW GaN THz QCL\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, achieving significantly lower operating currents that reduce the risk of thermal damage and improve the prospects for experimental realization. The inclusion of an additional barrier helps to suppress carrier leakage into the continuum and excited states however, while the current is reduced, it remains relatively high, and the added barrier makes energy level alignment more challenging.\u003c/p\u003e\u003cp\u003eA central achievement of our work lies in the successful reduction of doping density, which leads to a lower current density while still maintaining the desired gain performance. By the addition of a thin barrier within the wider well, we manage to maintain the gain performance of our previous studies with significantly lower doping density level and as a result to reduce the current density. In addition, employing the SWDP scheme simplifies the alignment of the electronic levels.\u003c/p\u003e\u003cp\u003eTo evaluate the carrier behavior and optical gain in the SWDP design, we performed a full-scale theoretical study using self-consistent simulations based on the non-equilibrium Green’s function (NEGF) formalism. This framework enables a quantum-level assessment of transport phenomena and gain characteristics by capturing the effects of quantum coherence and scattering processes\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. Our model includes both elastic and inelastic scattering channels that critically influence carrier dynamics. These involve ionized impurity scattering (IIS), alloy disorder, electron-electron (e-e) interactions, and interface roughness (IFR), alongside energy dissipating interactions with both optical and acoustic phonons. The interface morphology was modeled using a roughness amplitude of 1 Å and a correlation length of 80 Å, these parameter values follow commonly established conventions in the field and correspond roughly to the roughness of a single atomic layer at the interface\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e. A key aspect of our simulation is the inclusion of excited states. Ignoring these states can lead to an overly optimistic estimation of gain and an incomplete understanding of leakage paths\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Including these states enhances the predictive reliability of our model and demonstrates the practical viability of fabricating such a device.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Results and discussions","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e represents the conduction band diagram of an m-plane GaN THz QCL employing SWDP scheme. The structure is based on three subbands in each module. The layer sequence within one period, starting from the injection barrier, is as follows: \u003cb\u003e15\u003c/b\u003e/25/\u003cb\u003e10\u003c/b\u003e/28.5/\u003cb\u003e10\u003c/b\u003e/27.5 Å, with the barriers indicated in bold font. A sheet doping density of ~ 3×10\u003csup\u003e10\u003c/sup\u003e cm\u003csup\u003e− 2\u003c/sup\u003e is introduced in each period. The doped region is 15 Å wide, placed within the widest well, symmetrically on both sides of the split section. This configuration facilitates efficient electron injection. The injection barrier contains 14% Al, a value deliberately chosen to balance sufficient carrier confinement with material quality. A higher Al composition can introduce strain-induced defects, such as dislocations, that degrade crystal quality and device performance\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. The intrawell barrier, with a lower Al content of 7%, is inserted inside the wider well. This barrier has the same thickness as the injection barrier but reduced height, which facilitates resonant tunneling in addition to LO-phonon–assisted depopulation, thereby improving the efficiency of carrier extraction from the lower laser level. In the conduction band diagram, the ULL (level 2) is aligned with the injector level of the preceding module (level 1), enabling resonant tunneling. This strong coupling arise from the significantly stronger LO-phonon interaction in GaN, up to 16 times higher than in GaAs\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. The radiative transition occurs between level 2 (ULL) and level 3 (LLL). Electrons are then relaxed into the injector level (level 1′), and subsequently injected into the next period, continuing the lasing cycle. In this structure, the LLL (level 3) and the injector level of the next module (level 1′) are aligned to form a direct phonon scattering pathway, similar to the TW scheme\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The energy difference between the LLL and the injector level is ̴ 60 meV. The depopulation of the LLL is achieved via the combination of LO-phonon scattering and resonant tunneling to the next module.\u003c/p\u003e\u003cp\u003eFor further performance optimization, NEGF simulations were employed to model carrier transport and gain under room-temperature conditions.\u003c/p\u003e\u003cp\u003eOur optimization process included a detailed study of the doping level, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, where we present the simulated gain spectra at various doping densities. We began our investigation with a doping density of ̴ 3×10¹¹ cm⁻², which was previously identified as the optimal value in our earlier works\u003csup\u003e1\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e, yielding the highest peak gain. This doping density value is about one order of magnitude higher than the typical doping densities used in conventional GaAs-based THz QCLs. The motivation behind this study was to explore whether lower doping densities, comparable to those used in GaAs devices, could reduce the high current densities typically associated with highly doped structures while still maintaining sufficient gain. Contrary to the former assumption that increasing the doping density leads to higher gain, our results reveal the opposite trend. In our design, we observe a reduction in optical gain with increasing doping density, a trend primarily attributed to the relatively small energy separation between the LLL and the injector level (~ 60 meV). This limited spacing enhances the susceptibility of the structure to thermal backfilling, particularly at elevated doping levels, which in turn degrades population inversion and reduces gain\u003csup\u003e5\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. To address this, we implemented a barrier with reduced aluminum content (7% Al) inside the wider well, serving as a thin intrawell barrier. While its thickness matches that of the injection barrier, the lower Al concentration reduces the barrier height, thereby increasing the probability of resonant tunneling from the LLL to the injector level of the next module, in addition to LO-phonon–assisted depopulation. This combined mechanism enables faster and more efficient depletion of the LLL, which helps counteract the limitations imposed by thermal backfilling and supports gain performance with lower doping densities.\u003c/p\u003e\u003cp\u003eAs shown in the plot, we observe that as the doping density decreases, the peak gain increases. At low temperature, the highest peak gain was achieved with a doping density value of ̴ 6×10\u003csup\u003e10\u003c/sup\u003e cm\u003csup\u003e−2\u003c/sup\u003e. However, the highest operating temperature was obtained using a lower doping density value of ̴ 3×10\u003csup\u003e10\u003c/sup\u003e cm\u003csup\u003e−2\u003c/sup\u003e. Since the primary goal of our work is to achieve room-temperature laser emission, we selected a doping density value of 3×10\u003csup\u003e10\u003c/sup\u003e cm⁻² for our final simulations and design optimization.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e represents the current density as a function of voltage in different temperatures in the TW and Resonant Phonon (RP) and SWDP schemes. As can be seen from the figure, the current density reduced by almost a factor of two in the RP scheme in comparison to the TW scheme and by factor of four in the SWDP scheme in comparison to the TW scheme. This marked reduction significantly enhances the feasibility of realizing a functional experimental device and lowers the likelihood of thermal damage. While the operating current remains relatively high, the SWDP design nonetheless provides the greatest potential for successful experimental implementation.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e represents the optical gain versus photon frequency in various temperatures. These simulations include excited state contributions, which are essential for capturing realistic carrier dynamics, particularly at elevated temperatures. The peak of the curve corresponds to a photon frequency of ~ 8.7 THz. As the temperature increases, the gain remains relatively stable up to approximately 200 K, beyond which a clear decline is observed. Our simulation shows that at 10 K and in 280 K the gain values are ~ 42 cm\u003csup\u003e− 1\u003c/sup\u003e and ~ 17 cm\u003csup\u003e− 1\u003c/sup\u003e respectively which is above the estimated losses for double metal\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e very close to room temperature and shows the feasibility for high temperature operation. Our simulation includes all the scattering mechanisms and the excited states in order to show the feasibility of a practical device.\u003c/p\u003e\u003cp\u003eTo gain deeper insight into the physical processes limiting the performance of the device, we conducted a series of simulations in which each scattering mechanism was selectively eliminated, one at a time, while keeping all other scattering processes unchanged. This approach allowed us to isolate and assess the individual impact of each mechanism on optical gain. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the simulated optical gain as a function of photon frequency for each case. The simulations were carried out at a temperature of 10 K and a bias voltage of 95 mV/module. Our analysis underscores that the scattering mechanisms most strongly impacting the gain performance are primarily associated with IFR scattering. Among all the mechanisms examined, the removal of IFR scattering resulted in the most significant increase in peak gain. These findings highlight the critical importance of interface quality and suggest that further improvements in material growth and interface control could directly translate into enhanced device performance. This is particularly relevant for GaN-based structures, where growth technology is still under development and not as refined as the long-established GaAs growth methods. As a result, MBE growth in GaN systems tends to exhibit greater IFR. The elevated IFR in GaN/AlGaN heterostructures thus presents a significant challenge, directly impacting the optical gain. In addition, IIS and e–e interactions also contribute to gain suppression, though to a lesser extent. The influence of alloy disorder was found to be relatively minor under the simulated conditions. The simulation results are consistent with the fact that we use a relatively low doping density, which reduces the impact of e–e scattering and IIS, whereas IFR emerges as the dominant limiting mechanism due to the inherent challenges in achieving high-quality interfaces in GaN heterostructures.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, we have presented a theoretical investigation of a GaN-based THz QCL structure utilizing the SWDP scheme along the non-polar m-plane orientation. Using a self-consistent NEGF approach, we performed detailed simulations of carrier transport and optical gain, taking into account a full range of scattering mechanisms. The structure demonstrates promising performance, achieving a peak gain of ~\u0026thinsp;43 cm⁻\u0026sup1; at 10 K with the gain remaining above the estimated losses even at the elevated temperature of \u0026sim; 280 K, with an emission frequency \u0026sim;8.7 THz, a spectral range that lies beyond what has been realized with GaAs-based THz QCLs. The proposed structure effectively overcomes several limitations identified in previous studies, most notably the trade-off between high gain and low current density, which is critical for reducing the risk of thermal degradation. By incorporating a thin barrier within the wide well, we achieved a significant reduction in doping density, thereby lowering the current density while preserving robust gain performance. Furthermore, our scattering analysis reveals that IFR is the dominant mechanism limiting gain, a result that aligns with the known difficulties in achieving high-quality interfaces in GaN/AlGaN systems due to limitations in current epitaxial growth techniques. The use of a low doping level in our structure also reduces the impact of e-e scattering. These findings demonstrate that the SWDP-based GaN THz QCL design offers a practical route toward efficient, high-temperature THz laser sources, and lays the groundwork for future experimental realization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to acknowledge the Israel Innovation Authority for its grant provided through the Academic Applied Research Program, the Israel Ministry of Science and Technology for their grant for proposal 0007465, and the Israel Science Foundation for its grant (ISF 1755/23).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.\u003c/p\u003e\n\u003cp\u003eShiran Levy performed the simulations, analyzed the data, wrote the manuscript text, and contributed to the discussion of the results.\u003c/p\u003e\n\u003cp\u003eNathalie Lander Gower supported the data analysis and the writing process.\u003c/p\u003e\n\u003cp\u003eSilvia Piperno managed project administration, supported the writing process.\u003c/p\u003e\n\u003cp\u003eGad Bahir, supported the research and writing processes, funding acquisition.\u003c/p\u003e\n\u003cp\u003eAsaf Albo led the conceptualization, funding acquisition, investigation, project management, supervision, and the writing and editing of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported and funded by the Israel Innovation Authority, the Israel Ministry of Science and Technology and the Israel Science Foundation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest regarding this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMcIntosh, A. 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Phys.\u003c/em\u003e \u003cstrong\u003e57,\u003c/strong\u003e 081001 (2018).\u003c/li\u003e\n\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7711779/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7711779/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this work, we have theoretically investigated GaN-based terahertz quantum cascade laser (THz QCL) structure, modeled for growth along the non-polar m-plane. The design employs the split-well direct-phonon (SWDP) scheme and is analyzed using the Non-equilibrium Green\u0026rsquo;s Function (NEGF) approach. The proposed design successfully addresses key limitations identified in previous studies, particularly the challenge of balancing high gain with lower current density thereby mitigating the risk of thermal damage. By introducing a thin barrier within the wider well, we achieved a substantial reduction in doping density leading to lower current density while preserving strong gain performance. Our simulations show that the m-plane SWDP GaN-based QCL can achieve lasing at ~\u0026thinsp;8.7 THz, with 14% Al in the barrier and 7% Al in the intra-well barrier, with maximum operating temperature (Tmax) up to ~\u0026thinsp;280 K. This lasing frequency exceeds the typical limits of GaAs-based THz QCLs, demonstrating the potential of GaN-based designs for extended frequency coverage and high-temperature operation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e","manuscriptTitle":"m-Plane GaN Split-Well Direct-phonon Terahertz Quantum Cascade Laser","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-23 08:37:06","doi":"10.21203/rs.3.rs-7711779/v1","editorialEvents":[{"type":"communityComments","content":2},{"type":"decision","content":"Revision requested","date":"2026-04-13T11:31:51+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-13T08:38:47+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-13T01:02:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293568129834578777181473000956160289599","date":"2026-04-09T12:39:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"223733594571048252624117418893583637064","date":"2026-04-08T05:44:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"306156810252275013906942022978095047398","date":"2026-04-07T19:59:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-04T14:35:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"220135281038218071264405310402008147798","date":"2026-04-03T14:12:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"43982527167020189484556729591263344763","date":"2026-04-03T05:47:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"93161687521320567163376062270597965696","date":"2026-04-03T04:34:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-10T07:09:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"308074691892902505827742895099386672710","date":"2025-10-31T20:24:41+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-09T14:19:46+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-10-01T14:12:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-30T11:00:25+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-30T02:53:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-09-25T10:21:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"094c3c94-bf4e-47f5-8f60-846ec5183c6c","owner":[],"postedDate":"October 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":56664163,"name":"Physical sciences/Materials science"},{"id":56664164,"name":"Physical sciences/Optics and photonics"},{"id":56664165,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2026-05-19T11:09:44+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-23 08:37:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7711779","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7711779","identity":"rs-7711779","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}