Effect of interfacial formation on the properties of very long wavelength infrared InAs/GaSb superlattices

In InAs/GaSb superlattices (SLs) designed for infrared detection, the interfacial layers comprise approximately 10%–15% of the heterostructure. As interdiffusion into the InAs and GaSb layers is considered, this percentage is expected to be even higher. Although the primary goal for engineering these transient layers is to balance the SL strain to the GaSb substrate, the interfacial quality can impact the performance of the SL in other ways as well. Many believe that the majority of nonradiative defects that shorten carrier lifetime can be generated from the SL interfaces or regions near them due to the poor interface engineering. Because the degree of lattice mismatch tends to be higher in very long wavelength infrared InAs/GaSb designs, the approach tuning growth parameters to optimize the strain balancing process is different from that for midinfrared SLs. To investigate this optimization, a systematic approach was applied to achieve strain compensated 16 monolayers (MLs) InAs/7 MLs GaSb SLs aimed for a target onset wavelength of 15 μ m . The authors systematically explored the effect of growth parameters, such as group V fluxes, growth rates, and shutter sequences, on the SL strain and interfacial quality. For this study, high-resolution x-ray diffraction and atomic force microscopy analysis were extensively used to monitor the effect of interfaces on material properties.