Transverse-acoustoelectric-voltage (TAV) spectroscopy of high-resistivity GaAs

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Abstract
The space‐charge‐coupled interaction of surface acoustic waves (SAW) propagating on a piezolectric substrate with a semiconductor surface placed in proximity gives rise to a transverse acoustoelectric voltage. This voltage is developed across the semiconductor and is dependent on the semiconductor surface conductivity. Thus, the spectral response of the acoustoelectric voltage gives information about the interaction of impurity and defect levels of the semiconductors with the conduction and valence bands. Maxima and minima in the photoenhanced acoustoelectric voltage are due to corresponding structures in the photoconductivity. Experimental results on semi‐insulating gallium arsenide with no intentional doping, Cr doping, and Cr‐Te doping are reported. The results include the dependence of the acoustoelectric voltage on light intensity and on temperature. Peaks in the spectral response are interpreted as impurity levels. Thus, a sharp peak at 0.87 eV is attributed to Cr‐level–to–conduction‐band transitions and the broad peak centered about 0.72 eV is attributed to oxygen impurities. The absorption threshold determines the Fermi‐level location in the energy band and this, in turn, determines the sample resistivity. The experimental temperature dependence of band‐gap energy agrees with previously reported results. Photocurrent measurements were also performed and a remarkable correlation between the two spectra was obtained. An important advantage of the TAV technique is the fact that it is contactless, nondestructuve, and requires no special preparation.