Three-dimensional numerical simulation of planar P~+n heterojunction In_(0.53)Ga_(0.47)As photodiodes in dense arrays Part Ⅰ: Dark current dependence on device geometry

摘要

Low light level imaging applications requiring high detectivity demand photon shot noise limited performance at temperatures near 300K. Analytical models, however, have provided limited insight on underlying mechanisms limiting performance in conventional planar double heterointerface In_(0.53)Ga_(0.47)As on InP P~+n photodiodes for imaging the visible and short wave infrared. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we use three-dimensional numerical simulation to investigate intrinsically limited diffusion and Shockley-Read-Hall generation recombination dark currents for a planar P~+n photodiode situated in a 3×3 mini array. We assess the influence of geometry by varying pitch, junction location, and photodiode size. Modeling shows that SRH generation currents, not including surface effects, vary with both junction perimeter and area, and that the perimeter component dominates small radius junctions. By varying the axial junction placement we show that widegap junctions result in bias-dependent quantum efficiencies that require higher reverse bias, and result in higher dark currents, than shallow homojunctions at comparable efficiencies. Finally, numerical simulation explains lateral diffusion current suppression in dense arrays in terms of suppressed minority carrier density gradients. The analysis demonstrates that the boundary condition applicable to dense arrays requires no lateral diffusion current at symmetry planes bisecting segments connecting uniformly reverse biased nearest neighbor diodes. Following Grimbergen, this leads to radial geometry curves describing dark intrinsic diffusion reductions with pitch. The quantitative modeling provides insight explaining the observation that the ideal diode equation correctly estimates dense array dark diffusion currents.