Optimization of InAs/GaSb type-II superlattices for high performance of photodetectors

Abstract

The optimum growth conditions and strain balancing processes have been studied using molecular beam epitaxy (MBE) grown 51 A ̊ InAs/ 40 A ̊ GaSb type-II superlattices (SLs) designed to have cut-off wavelength of 10 μm . The most dominant factor in reducing the defect level in the SL structure was buffer growth temperature evidenced by transmission electron microscopy. In the study of the strain balancing process, the SLs could be lattice matched to the GaSb substrate by increasing the thickness of the InSb interfaces (IFs) from a nominal value of 1.0 to 1.4 ML , however, the structural quality degraded dramatically when the thickness of IFs reached beyond ∼1.0 ML . By optimizing the growth condition and MBE shutter sequences, micron thick InAs/GaSb SLs with a reduced lattice mismatch were routinely obtained with the full-width half-maximum of 18 arcsec , and the root mean square values of surface roughness of 2 A ̊ in 5 μm area scan of atomic force microscopy demonstrating high quality. Correlation between material quality and photoresponse signal strength in photoconductivity measurements was made on SL samples with cut-off wavelength on the order of 10 μm .