Use of a Schottky barrier to measure impact ionization coefficients in semiconductors

Abstract The use of a Schottky barrier to determine the impact ionization coefficients of electrons and holes in semiconductors has been studied analytically and also evaluated experimentally by comparing the results for silicon with those already available in the literature. The Schottky barrier offers several advantages over a diffused p-n junction in such measurements. Pure electron initiation and pure hole initiation can be separately achieved. The abrupt barrier provides an accurately known electric field, and the linearity of the field distribution simplifies the problem of extracting the ionization coefficients from the multiplication data. We present a general solution of the charge multiplication equation and derive expressions for the ionization coefficients for the particularly simple conditions that can be achieved in a Schottky-barrier junction. Our results for silicon in the range 2 × 105 α = α ∞ exp ( −b n E ) for electrons and β = β ∞ exp ( −b p E ) for holes, with α∞ = 9·2 × 105 cm−1, β∞ = 2·4 × 105 cm−1, bn = 1·45 × 106 V/cm and bb = 1·64 × 106 V/cm.