The Effect of GaSb Substrate Oxidation Layer on InAs/GaSb Type II Superlattice

Type-II superlattices (T2SLs) are emerging as next-generation materials for infrared detectors. The epitaxial quality of T2SLs is of great importance to the performance of infrared detectors such as dark current and detectivity. Herein, we explore the effect of the native GaSb oxide layer on the surface morphology and crystal quality of InAs/GaSb T2SLs grown with molecular beam epitaxy. The experimental results demonstrate that the thickness of the oxidation layer on GaSb substrates gradually increases over time and is saturated at around 73 angstrom in the natural oxidation condition. Moreover, the oxidation process is sensitive to humidity. As the thickness of the GaSb oxide layer increases from 18.79 angstrom to 61.54 angstrom, the full width at half maximum of the first satellite peak increases from 38.44 to 61.34 arcsec in X-ray diffraction measurements, and the root mean square roughness increases from 0.116 nm to 0.171 nm in atomic force microscopy measurements. Our results suggest that the thickness of the GaSb oxide layer should be less than 55 angstrom to obtain smooth buffer layers and qualified superlattices. The work provides an optimized direction for achieving high-quality superlattices for infrared optoelectronic devices.