Influence of shallow versus deep etching on dark current and quantum efficiency in InAs/GaSb superlattice photodetectors and focal plane arrays for long wavelength infrared detection

Abstract

In this paper, a comparison of quantum efficiency and dark current densities of shallow etched and deep etched InAs/GaSb type-II superlattice photodiodes is presented. The detectors were tailored for space applications with measured cut-off wavelengths around 11.2 µm. Bias and temperature dependencies of the QE have been studied showing very low turn on bias (>−25 mV) and very small variation of the peak QE value with temperature. At 70 K, peak quantum efficiencies of shallow and deep etched devices were deduced to 34% and 30%, respectively (without antireflection coating). The difference was attributed to a larger collection area of shallow etched devices, with a collection range of approximately 22 µm outside of the defined pixel area. Diffusion limited dark currents were observed down to 60 K for both shallow and deep etched devices under low reverse bias (∼−200 mV) with dark current densities on the order of 1.7 × 10−5 A/cm2 at 60 K. A gradually increasing influence of generation-recombination (G-R) and trap-assisted tunneling (TAT) was observed at lower temperatures for high reverse bias. The lowest dark current densities were observed for deep etched photodiodes, on the order of 3 × 10−7 A/cm2 at 40 K (Vbias = −100 mV). Detector arrays were fabricated with deep etched 30 µm pitch pixels. Comparably low dark current densities were observed for the detector array pixels under low reverse bias as for the single pixel photodiodes, however a significant increase of the TAT dark current was observed under high reverse bias.