Facets evolution of selected area grown GaAs in circular windows on Ge-on-Si and Ge substrates

We report the epitaxial growth of GaAs on Ge buffers on Si (001) substrates covered by SiO2 masks patterned with 3 mu m diameter circular windows by metalorganic chemical vapor deposition. The influence of As partial pressure on the crystal quality and facet evolution of GaAs was investigated. Scanning electron microscopy and atomic force microscopy revealed that the GaAs within the window region exhibited a relatively flat (001) crystal facet. Under high As partial pressures, the {111} facets of GaAs showed a pronounced orientation preference. At lower As partial pressures, the {111} and {110} facets of GaAs were roughly equally represented, aligning with the facet distribution structure predicted under As-rich conditions by the equilibrium crystal shape theory. The growth condition of high As partial pressure can effectively improve the growth quality of GaAs and obtain smooth GaAs film with a lower roughness. Due to the polarity mismatch between GaAs and Ge, antiphase domains persisted. We obtained GaAs samples free from antiphase domains and threading dislocations by utilizing a Ge 6 degrees offcut toward (111) substrate. This work introduces a feasible approach for heteroepitaxial integration of III-V semiconductor lasers, in particular the vertical cavity surface emitting lasers (VCSELs) on silicon substrates via direct growth, and the modulation of sidewall crystal facets for VCSELs.