A model for dark current and multiplication in HgCdTe avalanche photodiodes

In this paper we report the calculated results of the dark current and mult iplication factor in MBE grown HgCdTe avalanche photodiodes with separate a bsorption and multiplication (SAM-APD). The device architecture used for th is analysis comprises the following layers: p(+) contact, p junction, n(-) multiplication, n charge sheet, n(-) absorber, and n(+) contact. Various le akage current mechanisms are considered and the generation-recombination te rm is found to be the dominant one for this device structure. However, expe rimental reverse bias I-V characteristics reported earlier by T. de Lyon et al. shows a large deviation from ideality, which can not be explained in t erms of bulk leakage current mechanism. To explain the large difference bet ween experimental and theoretical data we consider that the dominant genera tion-recombination current is multiplied through impact ionization process. To validate this assumption, multiplication is calculated as a function of reverse bias. Electric field profile is obtained and the multiplication is computed using the ionization coefficients and avalanche gain equations. B reakdown voltage is found to be 85 V for room temperature operation in agre ement with available data in the literature. The theoretical I-V curves con sidering multiplication are compared with the experimental ones and a close agreement is found which validate this model.