Characteristics of InAs_0.8Sb_0.2 photodetectors on GaAs substrates

As an alternative to HgCdTe, InAs_xSb_1-x is an important alloy providing bandgaps suitable for infrared detection in both 3-5 and 8-12 μm atmospheric windows. There has been interest in high-quality growth of this material on GaAs and Si substrates. This paper reports the fabrication and characteristics of mid-infrared InAs_0.8Sb_0.2 photodetectors grown on GaAs substrates by molecular beam epitaxy. Peak detectivities of 1.4 × 10¹⁰ and 7.5 × 10⁸ cm Hz^1/2 W^-1 were measured at 77 K and 240 K, respectively, showing that the alloy is promising as an alternative to thermal detectors for near room temperature operation. A detailed analysis of the dark current showed that the reverse-bias differential resistance was limited by trap-assisted tunneling in a wide temperature range up to 150 K under low and moderately large reverse bias voltages. Noise measurements have shown that trap assisted tunneling is the source of 1/f noise which is increased with the addition of band to tunneling under large reverse bias. Our observations on InAs_0.8Sb_0.2 photodiodes show resemblance to those reported for HgCdTe detectors. The results are encouraging for the development of mid-infrared large area focal plane arrays on GaAs substrates.