Impact ionization in HgCdTe avalanche photodiode optimized to 8 μm cut-off wavelength at 230 K

If the impact ionization occurs in a region of high electrical field then it can result in avalanche multiplication of carriers. This process is used in avalanche photodiodes enabling individual photons to be detected when the incident flux of light is very low. HgCdTe is an almost ideal material for avalanche photodiodes, however to achieve the highest performance in near-room temperatures, a careful design of device structure is needed, to reach the highest performance in near-room temperatures. N+-nu-p-P+ photodiode meets the requirements of the separated absorption and multiplication regions. This paper describes the results of research aimed at investigation of the impact ionization mechanism in HgCdTe N+-nu-p-P+ photodiode optimized for 8 mu m cut-off wavelength at 230 K. The results show that the parameters of the nu-region greatly influenced on the distribution of the electric field and the generation rate due to the impact ionization. In addition, nu-region has the effect on reduction of undesirable tunneling in the space charge region. For this purpose, it is necessary to keep the doping in this region as low as possible and to extend the energy gap in relation to the absorbing region.