Abstract
AbstractCoupling of scanning tunneling microscopy (STM) with various schemes of optical spectroscopy was found to provide powerful tools for study of crystalline defects in bulk semiconducting solids. The simplest method was applied to a subsurface defect in a bulk GaAs crystal in which the signal was acquired by detecting the change in the tunneling current reflecting a local surface swelling that occurs when the wavelength of the chopped light used for spectroscopic measurements coincides with a photoabsorption spectral peak of the defect. Another scheme using a continuous light of variable wavelength was applied to midgap centers, assigned as arsenic antisite defects, densely populated in low-temperature-grown GaAs epifilms. Experiments at 90K revealed that light illumination causes reversible transformation of the individual defects to a metastable state with an excitation spectrum very close to one observed for the photo-quenching effect of EL2 centers in bulk GaAs.
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