Investigation of InGaAsSb-based heterojunction photodiodes for extended SWIR imaging

The detection in short wavelength infrared (SWIR) band, ranging from 1–3 μm, provides a wide range of applications in earth observation, plastics recycling, biology and hyperspectral imaging, gas analysis and defense. In this paper, uncooled InGaAsSb-based detectors for the wavelength range beyond 1.7 μm, the extended SWIR (eSWIR), are investigated for the later use in a thermographic traffic monitoring system that is supposed to localize potentially dangerous overheated hot-spot regions. Up to the wavelength of 1.7 μm, InGaAs lattice-matched with InP is used for photodetection in the SWIR. To reach a longer cutoff wavelength, "extended InGaAs" can be employed. This requires strained growth that leads to more growth defects and reduced yield, though. InGaAsSb, however, provides a tunable bandgap for detection beyond 1.7 μm and still enables lattice-matched growth on GaSb, which makes it a viable alternative for photodetection in the eSWIR. We have demonstrated that the bandgap of InGaAsSb can be tuned in the eSWIR by modifying the stoichiometry for lattice-matched growth on GaSb. Furthermore, we have successfully realized InGaAsSb heterojunction photodiodes with an AlGaAsSb hole barrier. At room temperature, the diodes achieve a dark current density of 0.5 mA/cm² and a responsivity better than 1 A/W resulting in an excellent peak detectivity of 9 x 10¹⁰ cm Hz^1/2/W. Thus, the highperformance detector arrays operating at room temperature are within reach in order to meet application demands.