Three-dimensional analytical model for photovoltaic detector arrays

Decreasing dimensions along with increasing number of elements in imaging photodiode arrays result in degradation of spatial resolution and sensitivity due to lateral transport(1-5). This effect is modelled using a novel 3-D analytical solution of the continuity equation. The model enables the full 3-D analysis of lateral transport as manifested in excess carrier distribution photocurrent, self and cross responsivities. Three detector structures are investigated: semi-infinite substrate, perfectly collecting, and perfectly reflecting backside. Front and rear illuminations are treated. Calculated results for the 3-D case deviate fundamentally from those predicted by the 1-D model. The 3-D model succeeds in explaining measured reduced quantum efficiency of small area detectors. It also predicts the observed limited effect of diffusion length on self responsivity and cutoff wavelength. Calculated spectral responses fit extremely well data measured on InSb and HgCdTe test arrays.