Nonequilibrium operation of arsenic diffused long-wavelength infrared HgCdTe photodiodes

We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated a p-on-n structure that we term P+/pi/N+ where the symbol "pi" is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 10(15) cm(-3)); P+ and N+ denote a higher doping density, as well as a higher energy gap, than the photosensitive base pi-region. Fabricated devices indicated that Auger suppression is seen in the P+/pi/N+ architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-mu m-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the pi-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths of 7.4 mu m and 10.4 mu m, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination.