INJECTION LUMINESCENCE FROM CDS(11(2)BAR-0) STUDIED WITH SCANNING TUNNELING MICROSCOPY

We have used a scanning-tunneling-microscope tip as a source of both electrons and holes to study injection luminescence from CdS(1120BAR) surfaces cleaved in UHV. Band-gap radiation and emission from radiative deep levels are resolved in optical spectra. Isochromat photon-intensity spectra exhibit, as a function of negative tip voltage, discrete steps which are discussed in terms of pair-creation thresholds. For positive tip polarity, hole creation in the valence band results in a continuous increase in the luminescence. Spatial maps of the resulting integrated light intensity acquired simultaneously with the conventional topographs reveal subnanometer-scale image contrasts which are attributed to defects, such as dislocations or radiative deep levels.