Shallow Levels Characterization in Epitaxial GaAs by Acousto-Optic Reflectance

Optical spectra of light reflection are detected under an influence of ultrasonic wave (UW)on a GaAs wafer. The differential spectrum is calculated as a difference between those taken under UW and without that influence on a sample. This acousto-optic differential reflectance(AODR) spectrum contains some bands that represent the energetic levels of the shallow centers in a sample. A physical basis of this technique is related to a perturbation of local states by UW. Here, a method is developed for characterization of local states at the surfaces and interfaces in crystals and low-dimensional epitaxial structures based on microelectronics materials. A theoretical model is presented to explain AODR spectra. Also, experiments using epitaxial GaAs structures doped by Te were made. Finally, theoretical and experimental results show that acousto-optic reflectance is an effective tool for characterization of shallow trapping centers in epitaxial semiconductor structures.