Carrier lifetime studies in Ge using microwave and infrared light techniques

The carrier lifetime in Czochralski (Cz) and float zone (FZ) grown Ge substrates as well as in optical-grade germanium has been studied by microwave reflection and transmission probing of optically excited lateral and cross-sectional areas. Pulsed excitation with wavelengths in the range between 532 and 3400 nm has been applied using YAG:Nd lasers and an IR parametric oscillator (IRPO). Surface recombination velocities larger than 70 cm/s and bulk lifetimes in the range between 30 ns and 500 μs were determined. It is observed that the carrier lifetime decreases with increasing conductivity and possible mechanisms are discussed. It is shown that the carrier recombination transients are driven by a system of recombination and trapping centers.