An analysis of the photoinduced current from a finely focused light beam in planar p-n junctions and Schottky-barrier diodes

We present analytic expressions for the photocurrent generated by a highly convergent light beam from a microscope objective lens incident on both planar p-n junctions and Schottky-barrier diodes. The variation of the current as a function of surface recombination velocity, depletion region width, diffusion length, and objective lens numerical aperture are all discussed. We also consider the application of the technique as a method of measuring minority-carrier diffusion lengths, which is independent of variations in surface reflectivity.