In Situ Strain Relaxation Comparison Between GaAsBi and GaInAs Grown by Molecular-Beam Epitaxy

The strain relaxation of GaAsBi is studied in order to determine both the maximum thickness before dislocations form for various misfits and the potential of GaAsBi for usage in the compositionally graded buffer of lattice-mismatched devices. Low-misfit GaAsBi epilayers are grown and compared with GaInAs, a well-studied material currently used in compositional grades. Relaxation behavior and dislocation energetics are compared using in situ wafer curvature. Samples are grown using molecular-beam epitaxy under similar conditions with misfit up to -0.81%. GaAsBi begins to relax at a lower thickness than GaInAs of the same mismatch. This leads to the majority of GaAsBi strain relaxation occurring with less material growth than comparable GaInAs. However, GaAsBi has greater residual strain than GaInAs after 2 μm of growth. These results indicate that GaAsBi requires less elastic energy to form dislocations and more elastic energy to either encourage glide or multiply dislocations than GaInAs. GaAsBi shows less surface roughness than GaInAs for all samples, ruling out roughness as a source of dislocations and hindered glide in these alloys.