TRANSIENT ACOUSTOELECTRIC SPECTROSCOPY MEASUREMENTS FOR THE CHARACTERIZATION OF GAAS EPILAYER STRUCTURES

A new measurement technique, acoustoelectric deep-level transient spectroscopy (AE-DLTS) is used to characterize the GaAs epilayer film grown on a semi-insulating GaAs substrate. The electric field, generated by the propagation of a surface acoustic wave (SAW) On a piezoelectric crystal, is used as a probing tool to study the transient behaviour of deep levels. This field interacts with the free carriers present in the semiconductor, resulting in an alteration of the carrier density at the surface of the semiconductor and the generation of a cc voltage. The rate at which excess charges are induced at the semiconductor surface, or diminished after the passage of the SAW pulse, is related to the position and the cross section of the deep levels at the interface between the epilayer and the substrate. The theoretical analysis of the fall time of the Dc voltage is presented along with experimental verification. In our experiments the voltage transients were recorded as a function of incident photon energy and at different temperatures, and the thermal and optical cross sections of the EL2 level in GaAs were evaluated from computer fit.