Bandgap tuning of InSb/InAsSb type II superlattices for multispectral sensing

We present numerical studies on InSb/InAs_1-xSb_x type-II superlattices (T2SL) for applications in multi-spectral-infrared detectors spanning peak detection wavelengths from 2.3 to 5.5 μm. The wavelength tuneability is achieved by varying the mole fraction x of the ternary compound indium arsenide antimonide (InAs_1-xSb_x) from 0.05 to 0.95. The simulated T2SL comprises 50 periods of 1.4 nm of InAs_1-xSb_x and 2.8 nm of indium antimonide (InSb). The use of T2SL structures allows to achieve bandgap tuneability, higher quantum confinement, lower noise and faster detection, leading to higher temperatures of operation compared to their bulk semiconductor counterpart, with similar performance. A T2SL p-i-n photodetector stack was simulated using software NextNano, simulating optical absorption with the energy bandgap of the T2SL tuned from 0.53 eV (2.3 μm in wavelength) to 0.22 eV (5.5 μm). The bandgap tunability of our simulated T2SL detector makes it possible to match the peak detection wavelengths to the absorption lines of several greenhouse gases such as methane and carbon dioxide. The simulated layer stack implements a multi-spectral detector suitable for epitaxial growth on gallium arsenide (GaAs) hence integration with GaAs-based readout electronics, enabling a monolithic multispectral imaging array technology, with applications in defence/security healthcare, and environmental monitoring.