The use of interfacial misfit dislocation filtering (IMF) using GaSb/GaAs interface has been garnering interest for III-V optoelectronics and high-speed transistors applications in recent years, due to its unique characteristics that allow rapid relaxation in the growth of highly mismatched heterostructures. This feature can be beneficial for applications in high-speed electronics, where materials with lattice constants of 6.0Å or beyond (i.e., InAs, GaSb, and InSb) have significantly higher carrier mobility. These materials are also useful in mid-infrared photodetector/emitters, hence allowing their growth on a more volume-friendly GaAs substrate opens up the possibilities for improved throughput in the existing mid-IR industries and new applications such as replacing the Ge cell low bandgap sub-cell on a III-V multi-junction solar cell structure.
Despite its known properties, the relaxation mechanism of IMF and how the growth parameters can be tuned to ensure a uniform formation of the misfit dislocation still require further study. In this work, a series of GaSb/GaAs samples were grown with a varying thickness between 12nm – 500nm. The samples were characterized using atomic force microscopy, x-ray diffraction, and spectroscopic ellipsometry. Cross-sectional transmission electron microscopy (TEM) was also used on selected samples to evaluate the IMF formation. Rapid relaxation of over 90% was observed in all samples, even on the GaSb sample grown only up to 12 nm thick. This rate of relaxation is far superior compared to existing graded buffer technique which requires a thickness of ~1 micron to bridge the lattice mismatch between GaAs and InAs. Ellipsometry analyses show that the complex dielectric function of the relaxed part of the GaSb film is very close to that of bulk GaSb, while the interface region exhibits various peak shifts, charge redistributions, and doping behaviours that strongly depend on the growth parameters.