A new technique to study transient conductivity under pulsed monochromatic light in Cr-doped GaAs using acoustoelectric voltage measurement

The transient conductivity of high-resistivity, Bridgman grown, Cr-doped GaAs under pulsed monochromatic light is monitored using transverse acoustoelectric voltage (TAV) at 83 K. Keeping the photon flux constant, the height and transient time constant at the TAV are used to calculate the energy dependence of the trap density and its cross section, respectively. Two prominent trap profiles with peak trap densities of approximately 10/sup 17/ cm/sup -3/ eV/sup -1/ near the valence and the conduction bands are detected. These traps have very small capture cross sections in the range of 10/sup -23/-10/sup -21 /cm/sup 2/. A phenomenon similar to the persistent photoconductivity with transient time constants in excess of a few seconds (in some cases, a few hundred seconds) in high-resistivity GaAs at T=83 K is also detected using this technique. These long relaxation times are readily explained by the spatial separation of the photo-excited electron-hole pairs and the small capture cross section and large density of trap distribution near the conduction band. The technique is nondestructive and, because of the dependence of the polarity of the acoustoelectric voltage on the carrier type, it yields information about the charge of the transient carriers and the type of deep traps involved in the release or trapping of these carriers.<>