Acousto-optical characterization of shallow states in GaAs:Te heterostructures

Interactions of light and ultrasonic wave (US) with shallow centers in the heterostructures GaAs:Te are investigated. Optical spectra of light reflection are taken at room temperature under an influence of US. A method is developed for characterization of local states at the surfaces and interfaces. A differential spectrum is calculated as a difference between those taken under US and without that influence. This acousto-optic differential reflectance (AODR) spectrum ΔR/R contains of some bands that represent the energetic levels of the shallow centers. A physical basis of the technique is connected to a simultaneous perturbation of the local states by light and US. The bands of AODR occur just at light energy corresponding to shallow energetic levels. The experiments with epitaxial GaAs:Te wafers are made. We find six different shallow levels with the ionization energies of 9 to 100 meV