Characterization of semiconductor heterostructures by acousto-optical perturbation technique

A new technique is developed for investigating defects at substrate/layer semiconductor interface. Acoustic waves (AW) are used to induce changes in the spectral dependence of the optical reflectance and transmission of semiconductor heterostructures together with photoacoustic (PA) and photoelectric (PE) imagings of the layers. The method is illustrated with experiments performed on n-type doped GaAs MBE layers of different quality (unintentionally doping and Si or Te controlled doping). The spectral peaks observed at about 37 and 29 meV inside the band gap are attributed to energy levels of Si and Te impurities, respectively. Two peaks ranged from 54 to 67 and 80–90 meV below the band gap in different samples are suggested to be due to two energy levels of As-vacancy related defects localized at the interface and influenced by electric fields and mechanical stresses in the boundary region. The exact energy position of these peaks is interpreted to be indicative of the interface quality. PA and PE imagings are employed to qualitatively determine electric charge conditions of the interface. It is demonstrated that the nonuniformity of the PE image increases for lower quality substrate/layer interface. Direct evidence is found that relates the interface charge to the spectral peak position of the As-vacancy related defect in acoustically perturbed reflectance spectra.