Impact ionization investigations on ZnSe Schottky barrier diodes

Multiplication processes have been investigated on Au–n-ZnSe Schottky diodes by optical injection of initiating carriers into the space charge region in the electric field range of 5.5 × 105 V/cm < F < 7 × 105 V/cm. Using the photoemission of electrons from the Au-contact over the metal–semiconductor barrier the pure electron-initiated multiplication factor Mn has been measured. However, the hole-initiated multiplication factor Mp by backside excitation of the diode with hv ≈ Eg could not be used since the hole diffusion length Lp has been found to be very small. But from theory it can be shown that Mp can be evaluated from the measured multiplication factors Mn and Mnp; Mnp represents the multiplication initiated simultaneously by electrons and holes in the space charge layer. On the basis of this method in the first order approximation Mn ≈ Mp. Applying the analytical approximations proposed by Okuto and Crowell to the measured field dependence of the ionization coefficient one arrives at a “mean free scattering length” λ ≈ 45 Å, depending on the assumed mean threshold energy Ei.