Lifetime of Injected Carriers in Germanium

A method is described for the determination of the lifetime of injected carriers in a semiconductor by measuring the variation of the sample conductance after a voltage pulse has produced excess carriers. Volume and surface recombinations are separated by varying the sample dimensions. It is shown that carefully etched surfaces give very small surface-recombination velocity. The lifetime in high-resistivity germanium does not correlate critically with the resistivity, but can be changed greatly by heat treatment. Quenching from temperatures above 500°C reduces the lifetime drastically before the resistivity is appreciably affected. Preliminary measurements on some N-type as well as P-type germanium samples at low temperatures indicate that the lifetime first decreases upon cooling from room temperature, but the N-type samples at liquid nitrogen temperatures show a rapid decay of excess conductance superimposed on a much longer decay.