Computer controlled microwave transient photoconductivity for the nondestructive characterization of GaAs substrates

In this paper we describe a nondestructive, contactless and fast characterization method for GaAs high-resistivity wafer substrates. Our method can be referred to as computer-controlled microwave transient photoconductivity. This method is based on the microwave measuring at 36.4 GHz of transient photoconductivity exited by laser pulse. The automatic measurements and computer simulation of experimental data make it possible to separate the multiple-rate decay mechanisms of transient photoconductivity. Our setup enables measuring the relaxation times ranging from 10−8 to 10−4 s in the temperature range from 80 to 300 K. The temperature dependence analysis of the photoconductivity permits determination of the activation energy and thermal capture cross section in doped wafer substrates. To demonstrate the possibilities of the method, we present experimental data obtained on two GaAs substrates.