| Abstract Scope |
The growth window for achieving high-quality photonic device structures on (111) GaAs by conventional molecular beam epitaxy (MBE) is very narrow. For this reason, the vast majority of fabricated GaAs-based photonic devices are synthesized on (100)-oriented substrates. However, strained and unstrained structures produced on (111) substrates offer a new class of electronic and optoelectronic devices that benefit from the piezoelectric effect- a feature that is not accessible on symmetric (100) orientations. In this work, we report on a series of investigations of strained and unstrained structures that include GaAs, AlGaAs/GaAs, and InGaAs/AlGaAs multi-quantum wells deposited on epi-ready GaAs (111)B 2°→[21 ̅1 ̅ ] Si-doped substrates by conventional molecular beam epitaxy. The difficulty with high-quality thin film deposition on (111)-oriented surfaces stems from its sensitivity to V-III ratio and substrate temperature, specifically the nucleation of adsorbed species and adatom migration lengths, which differ significantly from deposition on (100) GaAs surfaces. During this study, we reference the identification of the four temperature related surface reconstructions: (1x1)HT, (√19 x √19), (1x1)LT and (2x2), that are associated with the (111)B GaAs surface via in-situ reflection high energy electron diffraction (RHEED). In an effort to adequately examine the surface morphology for various strained and unstrained quantum well structures, a parameter space that includes surface reconstruction, substrate temperature, and a beam equivalent pressure (BEP) is explored. Under identical deposition conditions, direct comparisons are accomplished for strained and unstrained quantum well structures on GaAs (100) and GaAs (111) surfaces. A statistical experimental design is also employed, where the V/III ratio and substrate temperature are selected within the (√19 x √19) surface reconstruction phase. Using a scanning electron microscope (SEM) and an atomic force microscope (AFM), surface morphology was studied and demonstrates a strong correlation with V/III BEP ratio and substrate temperature. For smooth samples, AFM and SEM results show surface roughness of ~0.24nm across a 1x1µm2 area and a significant decrease in the pyramidal hillock density across the wafer. As the growth parameters are optimized, strained and unstrained structures that take advantage of the piezoelectric properties can be produced. |