Photoconductivity Decay in Imperfect Crystals

Abstract

The photoconductivity decay in imperfect crystals can be described in terms of an exponential trap distribution, Nt(E) = N0 exp(− E/kT*), where N0 and T* are two parameters characteristic of the distribution. Theoretical expressions for the decay as a function of excitation intensity and temperature can be derived in terms of N0 and T*, both of which can be determined from a Fermi-level analysis of the experimental decay curves. Such an analysis of experimental curves is carried out for a Cd(SSe) sintered photoconductor layer, and it is shown that an approximately exponential trap distribution with N0=2.0×1017 cm−3 eV−1 and T* = 852°K exists at least between 0.3 and 0.6 eV below the conduction band. The theoretical expressions, involving no additional undetermined parameters, are then used to calculate decay curves as a function of temperature between 298° and 348°K, and as a function of excitation intensity over two orders of magnitude, with satisfactory agreement with the experimental curves. It is concluded that the photoconductivity decay characteristics of imperfect crystals can be described over rather wide ranges of temperature and excitation intensity by specifying the electron lifetime, τ, and the two trap distribution parameters, N0 and T*.