COMPUTER-CONTROLLED MICROWAVE TRANSIENT PHOTOCONDUCTIVITY FOR THE NONDESTRUCTIVE CHARACTERIZATION OF GAAS SUBSTRATES

In this paper we describe a nondestructive, contactless and fast chara cterization method for GaAs high-resistivity wafer substrates. Our met hod can be referred to as computer-controlled microwave transient phot oconductivity. This method is based on the microwave measuring at 36.4 GHz of transient photoconductivity exited by laser pulse. The automat ic measurements and computer simulation of experimental data make it p ossible to separate the multiple-rate decay mechanisms of transient ph otoconductivity. Our setup enables measuring the relaxation times rang ing 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 secti on in doped wafer substrates. To demonstrate the possibilities of the method, we present experimental data obtained on two GaAs substrates. (C) 1997 Elsevier Science S.A.