Monte Carlo simulations of the cross talk due to minority carrier diffusion in back illuminated InSb matrices are presented. These calculations are done in three dimensions, and accurately take into account the non-uniform boundary conditions on the front surface. Values of the cross talk for first, second, and third nearest neighbors are obtained along with the theoretical quantum efficiencies for a variety of device geometries and material parameters. In particular, the dependence of cross talk and quantum efficiency on junction size and pitch, for both planar and mesa diodes with and without guard rings is derived. The effects of material and processing parameters such as minority carrier lifetime and diffusion length, surface recombination velocity, absorption coefficient, and InSb layer thickness are also shown. Results of these simulations show that the quantum efficiency and cross talk are strongly dependent on the surface recombination velocity and matrix dimensions, however they are relatively insensitive to the material parameters over a wide range of values. Calculated point spread functions are presented for selected cases, and are seen to display an interesting `nearest neighbor guarding' effect.