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 mu s 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. (C) 2006 Elsevier Ltd. All rights reserved.