C-band All III-Arsenide InAs Quantum Dot Lasers on InP using Low Indium Composition Partial Capping

C-band All III-Arsenide InAs Quantum Dot Lasers on InP using Low Indium Composition Partial Capping | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Electronics Letters This is a preprint and has not been peer reviewed. Data may be preliminary. 10 February 2025 V1 Latest version Share on C-band All III-Arsenide InAs Quantum Dot Lasers on InP using Low Indium Composition Partial Capping Authors : Jinkwan Kwoen 0000-0002-5273-3981 [email protected] , Jihye Jung , Masahiro Kakuda , and Yasuhiko Arakawa Authors Info & Affiliations https://doi.org/10.22541/au.173915647.73952693/v1 Published Electronics Letters Version of record Peer review timeline 321 views 189 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract This study demonstrates the growth of InAs quantum dots (QDs) on InP substrates using an all group III-arsenide approach in molecular beam epitaxy (MBE) with a low-indium-composition InAlGaAs partial capping layer. Real-time curvature measurements confirm effective strain compensation during multilayer QD growth, enabling precise control of emission wavelength and structural stability. The fabricated lasers exhibited successful operation at a telecommunication C-band. C-band All III-Arsenide InAs Quantum Dot Lasers on InP using Low Indium Composition Partial Capping Jinkwan Kwoen, Jihye Jung, Masahiro Kakuda and Yasuhiko Arakawa Institute for Nano Quantum Information Electronics, The University of Tokyo, 4-6-1 Komaba Meguro-ku, Tokyo, Japan Email: [email protected] , [email protected] . This study demonstrates the growth of InAs quantum dots (QDs) on InP substrates using an all group III-arsenide approach in molecular beam epitaxy (MBE) with a low-indium-composition InAlGaAs partial capping layer. Real-time curvature measurements confirm effective strain compensation during multilayer QD growth, enabling precise control of emission wavelength and structural stability. The fabricated lasers exhibited successful operation at a telecommunication C-band. Introduction: Quantum dot (QD) lasers [1] have garnered significant attention as next-generation optical materials due to their unique properties, such as low threshold current, high operation temperature, and exceptional temperature stability [1–4]. These characteristics make QD lasers particularly promising for various applications, including silicon photonics, where high operational stability and performance are critical[5]. While earlier studies primarily focused on O-band (1.3 μm-band) QD lasers based on InAs/GaAs, recent efforts have shifted toward developing C-band (1.55 μm-band) lasers utilizing InAs/InP QDs for telecommunication C-band applications. Typically, the growth of these QDs on InP substrates involves the concurrent use of group V materials, such as arsenic (As) and phosphorus (P), in molecular beam epitaxy (MBE). However, this conventional approach presents notable challenges. For instance, the use of white phosphorus, which is highly toxic and spontaneously flammable, introduces safety concerns and complicates the fabrication process. Additionally, precise control of the phosphorus and arsenic flux during growth requires specialized equipment, such as dedicated phosphorus cells, pumps, and safety traps, which increases both cost and complexity. To address these challenges, we successfully demonstrated the growth of InAs QDs using an all group III-arsenide (III-As) approach in MBE and developed a L-band (1.6 μm-band) laser based on these QDs [6]. By inserting a thin GaAs layer between the InAlGaAs buffer layer and the InAs QD growth layer, we achieved the successful growth of InAs QDs even on high-indium-composition III-As materials lattice-matched to InP. The grown QDs exhibited emission near 1.8 μm without additional treatments and were subsequently blue-shifted to shorter wavelengths through techniques such as partial capping and indium flush [7]. Single-layer QD structures demonstrated room-temperature photoluminescence (PL) emission at the 1.5 μm band. However, in multilayer QD structures under current injection in laser devices, a redshift in emission to approximately 1.62 μm was observed [6]. This redshift is attributed to strain accumulation caused by QD stacking, leading to increased QD size in the upper layers. Other studies have employed strain compensation techniques [8–11], indium-flush method [12] and ex-situ rapid thermal annealing [13] to overcome limitations in stacking multiple QD layers. For instance, researchers succeeded in stacking 300 layers of InAs QDs on InP(311) substrates by employing a strain-compensation method, effectively eliminating the strain buildup that would normally limit the number of stackable layers [10]. In contrast, our study adopts a different strategy by adjusting the indium composition of the capping layers to control both strain and indium interdiffusion, presenting a novel method to achieve precise emission wavelength tuning in QD structures. In this study, we report the growth of InAs QDs using a low-indium-composition InAlGaAs capping layer and the demonstration of C-band QD lasers based on this approach. This method offers several advantages: the InAs QDs are capped with a material having a smaller lattice constant than InP, facilitating blue-shifting to shorter wavelengths. Additionally, strain relaxation is achieved, mitigating the redshift associated with QD stacking in multilayer structures. Furthermore, the lower indium composition of the capping layer enhances control over the indium flush process, providing better tunability during fabrication. Experimental method: The epitaxial growth of the sample structure was carried out using a RIBER Compact 21 T solid-source molecular beam epitaxy (MBE) system. The curvature of the wafer throughout the entire growth process was measured using a magnification inferred curvature (MIC) technique[14, 15]. For the Group III elements, Gallium (Ga), Indium (In), and Aluminum (Al) were utilized, supplied via standard dual filament effusion cells. Arsenic dimer (As 2 ) was employed as the Group V source throughout the growth process. Silicon (Si) and Beryllium (Be) were used as n-type and p-type dopants, respectively. The substrate, a quarter of a 3-inch n-type InP(001) wafer, was initially heated to 530°C under an arsenic atmosphere to desorb the native oxide layer. The epitaxial layer structure began with the growth of a 200-nm-thick In 0.52 Al 0.48 As lower buffer layer directly on the InP substrate. This layer, lattice-matched to the substrate, featured a low refractive index suitable for optical confinement. Subsequently, a 100-nm-thick In 0.52 Al 0.24 Ga 0.24 As waveguide layer, also lattice-matched to the InP substrate, was grown. A eight-layer stacked QD structure was then fabricated. Each QD layer began with the deposition of a 1-nm-thick GaAs layer [6], which served to reduce the diffusion length of Indium adatoms, followed by the deposition of three monolayers (MLs) of InAs. Directly above the QD, a 4-nm-thick In 0.35 Al 0.325 Ga 0.325 As partial capping layer was grown, flowed by the application of an indium flush [16]. A 16-nm-thick In 0.52 Al 0.24 Ga 0.24 As spacer layer was grown after each QD layer. Following the stacked QD structure, an additional 64-nm-thick In 0.52 Al 0.24 Ga 0.24 As layer was deposited. The structure was completed with the growth of a 1700-nm-thick In 0.52 Al 0.48 As upper cladding layer, followed by a 200-nm-thick In 0.53 Al 0.47 As p-type contact layer. The complete epitaxial layer structure can be shown in Figure 1. We subsequently fabricated the prepared sample into a traditional Fabry–Perot (FP) laser. The p-type electrode used 20-nm Pt/30-nm Ti/20-nm Pt/400-nm Au, while the n-type electrode used 30-nm AuGeNi/400-nm Au. We deposited the p-type electrode in a stripe pattern with a width of 100 μm. The n-type electrode was deposited on the backside of the InP substrate. Following these steps, the sample was then cleaved to 1000 μm. High-reflection coating was not applied to the laser facets. Results and discussion: To monitor the strain evolution during the growth of InAs QD laser structures on InP substrates with low-indium-composition InAlGaAs partial capping layers, real-time curvature measurements were conducted. Figure 2(a) shows the curvature changes for three partial capping layers with indium compositions of x=0.35, x=0.52, and x=0.57. The curvature evolution for each composition demonstrates the sequential induction of compressive and tensile strains during the deposition of GaAs, InAs QDs, and InAlGaAs capping layers. Notably, significant curvature reduction is observed during InAs deposition, followed by curvature recovery during the growth of the InAlGaAs capping layer. The differences in strain responses among the various indium compositions highlight the role of the partial capping layer in strain management during QD growth. For x=0.35, the nearly identical curvature values at the beginning and end of a single layer suggest reduced strain accumulation in the capping and spacer layers compared to compositions such as x=0.52, which matches the InP lattice, or x=0.57, which exceeds the lattice constant. This implies less tensile strain left in the capping layers and spacer layers, leading to reduced deformation in the upper QD layers. Figure 2(b) depicts the curvature changes during the growth of the entire QD laser structure. Initially, compressive strain arises due to thermal expansion mismatch between the upper and lower sides of the substrate at the high temperature required for deoxidation. In the QD stacking region, the tensile strain induced by InAs and the compressive strain resulting from the low-indium-composition partial capping layers and indium flush are observed to be effectively compensated. This indicates successful strain compensation during the multilayer growth process, a critical factor in ensuring structural stability in the final device. Moreover, the upper clad layer of InAlAs and the contact layer of InGaAs, lattice-matched to InP, exhibit minimal curvature changes during growth. The abrupt curvature reduction observed in the final stage reflects the changes due to thermal expansion mismatch between the upper and lower sides of the substrate as the wafer is cooled to room temperature. The fabricated lasers were characterized under pulsed mode operation. Figure 3 presents the light-current (L-I) characteristics of an FP laser at 25°C, having a cavity length of 1000 μm and a width of 100 μm. The laser exhibited a threshold current of 3.1 A and a threshold current density of 3.1 kA/cm 2 , respectively. The laser operated multi-mode regime lasing with a central lasing wavelength of 1537 nm. The intensity saturation observed in the L-I curve at higher current densities can be attributed to thermal effect. Conclusion: This study successfully demonstrates the growth of InAs QDs on InP substrates using a novel all group III-As approach, coupled with low-indium-composition InAlGaAs partial capping layers for strain management and emission wavelength tuning. Real-time curvature measurements reveal effective strain compensation, contributing to the structural stability of multilayer QD structures. The fabricated laser exhibited lasing at 1537 nm with a threshold current density of 3.1 A/cm², confirming the feasibility of this approach for developing high-performance telecom lasers. This method enables precise control over strain and emission properties, paving the way for future advancements in C-band QD-lasers with high-temperature operation, which is essential for photonic network systems. Author contributions: Jinkwan Kwoen: Conceptualization; Data curation; Formal analysis; Investigation; Methodology; Resources; Software; Validation; Visualization; Writing – original draft; Writing – review & editing. Jihye Jung: Investigation; Methodology. Masahiro Kakuda: Investigation; Methodology. Yasuhiko Arakawa: Conceptualization; Funding acquisition; Investigation; Project administration; Supervision; Writing – review & editing Acknowledgments: This paper is based on results obtained from a project, JPNP16007, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and a project, JPMJMS2064, by Japan Science and Technology Agency (JST) and supported by JSPS KAKENHI Grant Number JP23K04598. The authors would like to thank Prof. Dr. Satoshi Iwamoto for the fruitful discussions on this study. Conflict of interest statement: The authors declare no conflict of interest. Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.  2024 The Authors. 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Lett. , 2024, 125 , (17), p. 5. 16 Kwoen, J., Kakuda, M., Arakawa, Y.: ‘Wide-range Emission Wavelength Control of InAs Quantum Dots by Changing Indium Composition in InAlGaAs Partial Capping Layer’ (2024) Supplementary Material File (image1.emf) Download 746.68 KB File (image3.emf) Download 240.99 KB File (image5.emf) Download 357.35 KB Information & Authors Information Version history V1 Version 1 10 February 2025 Peer review timeline Published Electronics Letters Version of Record 25 May 2025 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Electronics Letters Keywords molecular beam epitaxial growth quantum dot lasers semiconductor quantum dots Authors Affiliations Jinkwan Kwoen 0000-0002-5273-3981 [email protected] The University of Tokyo View all articles by this author Jihye Jung The University of Tokyo View all articles by this author Masahiro Kakuda The University of Tokyo View all articles by this author Yasuhiko Arakawa The University of Tokyo View all articles by this author Metrics & Citations Metrics Article Usage 321 views 189 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Jinkwan Kwoen, Jihye Jung, Masahiro Kakuda, et al. C-band All III-Arsenide InAs Quantum Dot Lasers on InP using Low Indium Composition Partial Capping. Authorea . 10 February 2025. DOI: https://doi.org/10.22541/au.173915647.73952693/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. 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