Improved local field model for HgCdTe electron avalanche photodiode

Abstract

HgCdTe linear avalanche photodiodes (APDs) have been extensively studied, due to the excellent performance in low excess noise, as well as linear tunable gain at low reverse bias. In this paper, an improved local field model was presented based on the Okuto-Crowell model. It can explain the calculation deviations from our experimental gain data, which gain was simulated based on the local field model by Rothman and ballistic model. The electric field distribution was assumed to be a constant in local field model, which is the approximation of the situation for ultra-low carrier concentration with range of 1014 cm−3 or less. Nevertheless, it cannot fit the situation with high N− concentration if greater than 1 × 1015 cm−3. In our work, the APD gain was simulated by integration over the whole junction, which is under the influence of electric field distribution based on the Poisson equation. Compared with the commercial TCAD software Sentaurus, the simulation results by improved model indicated the similar accuracy, which cut down the calculation time from over couples of hours to several seconds. Besides of gain and dark current, the results also may indicate that the parameters of N− region greatly impacted on the threshold voltage for impact ionization, including junction width, N− concentration, Cd composition of Hg1-XCdxTe as well.