MTL Annual Report

Heteroepitaxy of polar and non-polar semiconductors has long been a challenge for integrating different semiconductor material systems. Previous research in our group has demonstrated high-quality GaAs heteroepitaxy on Ge substrates with low defect density. Anti-phase boundary (APB) formation was suppressed by using offcut substrates and a precisely controlled surface preparation technique ^[1]. Recently, we have demonstrated high-quality heteroepitaxy of Ge on GaAs and tensile-strained Ge on InGaAs by employing surface preparation procedures that ensure a pre-growth surface with a high V-to-III ratio ^[2]. Extending these results, we were able to grow high-quality Ge films on an AlAs underlayer and demonstrate an epitaxial-liftoff technique to transfer Ge films to arbitrary substrates, as shown in Figure 1. The transfer was realized through sacrificial etching of the AlAs underlayer in a diluted HF solution.  In another project, we grew a high-quality 40-period GaAs/AlAs distributed Bragg reflector (DBR) on Ge substrate. Figure 2a shows cross-section TEM image of the first 5 periods of the DBR. After patterning, the Ge substrate was then sacrificially etched via a XeF₂ gas-phase etching to release the cantilever-shaped DBRs, shown in Figure 2b. These DBR cantilevers form micro-optomechanical resonators with excellent resonant characteristics. Our current project builds on these results and explores a method to make GaAs-on-insulator substrate on the 6-inch scale via lateral etching of an epitaxial Ge sacrificial layer.

1. Ting, S.M. and E.A. Fitzgerald, Metal-organic chemical vapor deposition of single domain GaAs on Ge/GexSi1-x/Si and Ge substrates. Journal of Applied Physics, 2000. 87(5): p. 2618-2628. [↩]
2. Bai, Y., et al., Growth of highly tensile-strained Ge on relaxed InxGa1-xAs by metal-organic chemical vapor deposition. Journal of Applied Physics, 2008. 104(8). [↩]