Recombination of Excess Carriers in Semiconductors

The recombination of excess carriers in semiconductors is discussed on the basis of a model in which the recombination occurs through multiple-levels. The theory is extended to apply to germanium. The dependence of carrier lifetime on temperature in most of pure n -type germanium samples can be explained by introducing two sets of traps, recombination centers ( E C - E r =0.30eV) and hole trapping centers ( E t - E V =0.30eV), in our temperature range. However, the minority carrier lifetime of samples containing comparatively high dislocation density (10 4 –10 5 /cm 2 ) is shown to vary with the dislocation density, and the results is expressed in terms of two lifetimes: τ d , that associated with random dislocations, and τ b , that due to the recombination centers of an undetermined origin. It is also shown that anomalous temperature dependence of the steady-state photoconductivity of high-resistivity p -type nickel doped germanium can be interpreted by assuming that two acceptor levels of nickel atom are effective at the same time, but different in the effect on the recombination process.