Quantitative analysis of effects causing nonlinear position response in position-sensitive photodetectors

Although it is theoretically possible to construct light-spot-position-sensitive photodetectors (PSD´s) having perfect position-response linearity, in practice linearity is degraded by laterally inhomogeneous resistive layers, finite-conductive strips, and imperfect isolations. PSD´s at 6 × 6 mm²having 0.5-percent nonlinearity have been fabricated, but before making larger PSD´s with less nonlinearity, e.g., for use in silicon repeaters, a quantitative analysis of the causes of nonlinearity must be made. To this end, a computer model is developed. This model is described here, and the results of calculations performed with it are discussed. Nonlinearity caused by inhomogeneity is found to be less than 1/8 of the maximum relative change in resistive layer conductivity. It further appears that finite-conductive contact strips cause less than 0.05-percent nonlinearity if the contact strips are wide enough. Nonlinearity due to imperfect isolations is important only when n-n^-or p-p^-junctions are used. The calculations derived are found to be in good agreement with results given in the literature.