Dependence of carrier lifetime in germanium on resisitivity and carrier injection level

The dependence of carrier lifetime on resistivity and carrier injection level in germanium crystals is studied using microwave probing of optically excited samples. Bulk lifetimes in the range between 30ns and 500μs are measured. The carrier lifetime decreases with decreasing resistivity and increases with increasing excitation level. Possible mechanisms are discussed and it is shown that the carrier recombination transients are driven by a system of recombination and trapping centers.