(Invited) InAs/InAs1-XSbx Type-II Superlattices for High-Performance Long-Wavelength Infrared Medical Thermography

After being proposed by Sai-Halasz et al. in 1977, type-II superlattices (T2SLs) have demonstrated themselves as a very important material system in various fields such as lasers, photodetectors and transistors. In the field of infrared detection and imaging, InAs/GaSb T2SLs have become a viable candidate to compete with the state-of-the-art mercury-cadmium-telluride (MCT) compounds material system. By spatially separating electrons and holes into different quantum wells, the type-II band alignment enables the full control of the electronic bandstructure and thus, allows for great flexibility in hetero-structure device designs. Beside InAs/GaSb type-II superlattices, InAs/InAs_1-xSb_xT2SLs have been proved to have a longer carrier lifetime than InAs/GaSb T2SLs and have been proposed as an alternative for infrared photodetectors.

We report demonstration of a high performance long-wavelength infrared nBn photodetectors based on InAs/InAs_1-xSb_x type-II superlattices on GaSb substrate. The photodetector’s 50% cut-off wavelength was ~10 mm at 77K. The photodetector with a 6 mm-thick absorption region exhibited a peak responsivity of 4.47 A/W at 7.9 mm, corresponding to a quantum efficiency of 54% at -90 mV bias voltage under front-side illumination and without any anti-reflection coating. With an R×A of 119 Ω·cm² and a dark current density of 4.4×10^-4 A/cm² under -90 mV applied bias at 77 K, the photodetector exhibited a specific detectivity of 2.8×10¹¹ cm./W.