Characterization of semiconductor heterostructures by acousto-optical perturbation technique

A new technique is developed for investigating defects at substrate/layer s emiconductor interface. Acoustic waves (AW) are used to induce changes in t he spectral dependence of the optical reflectance and transmission of semic onductor heterostructures together with photoacoustic (PA) and photoelectri c (PE) imagings of the layers. The method is illustrated with experiments p erformed on n-type doped GaAs MBE layers of different quality (unintentiona lly 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 80-9 0 meV below the band gap in different samples are suggested to be due to tw o energy levels of As-vacancy related defects localized at the interface an d influenced by electric fields and mechanical stresses in the boundary reg ion. The exact energy position of these peaks is interpreted to be indicati ve of the interface quality. PA and PE imagings are employed to qualitative ly determine electric charge conditions of the interface. It is demonstrate d that the nonunifornity of the PE image increases for lower quality substr ate/layer interface. Direct evidence is found that relates the interface ch arge to the spectral peak position of the As-vacancy related defect in acou stically perturbed reflectance spectra. (C) 2000 Elsevier Science S.A. All rights reserved.