Dember effect in fast photoconductive circuit elements

The observed independence of mobility on surface conditions in InP:Fe fast photoconductivity devices is explained by inclusion of the Dember electric field resulting from unequal electron and hole mobilities. From the calculated electron-concentration distribution as a function of the distance normal to the device surface, we determine that the mean position of the electron concentration in InP lies more than one standard deviation below the surface for laser excitation of 780 nm and a high-injection ambipolar surface recombination velocity of 10⁶cm/s. Results are presented for InP:Fe as a function of surface recombination velocity, and related results are presented for Si and for a material with equal hole and electron mobilities.