EBIC Spectroscopy - A New Approach to Microscale Characterization of Deep Levels in Semi-Insulating GaAs

We propose a new approach to the defect characterization in semiinsulating (SI) GaAs which combines the high spatial resolution and scanning capability of the Electron Beam-Induced Current (EBIC) mode of Scanning Electron Microscopy (SEM) with the advantages of optical and thermal spectroscopies employed in the identification of deep levels. In the PHOTO-EBIC approach a DC electron beam and a chopped subbandgap monochromatic light impinge on the SI GaAs through a semi-transparent Au electrode. The photoinduced modulation of the EBIC as a function of the subbandgap energy of incident photons constitutes a structure which corresponds to the photoionization of deep levels. In the thermally stimulated EBIC (TS-EBIC) the deep levels are filled at low temperature by the excess carriers generated by an electron beam. Subsequently, the changes of EBIC as a function of temperature constitute a spectrum of peaks which correspond to different deep levels. The peak position determines the deep level energy while the magnitude of peaks can be used for the assessment of the relative concentration of deep levels located within the small volume probed by the electron beam.