Low energy cathodoluminescence spectroscopy of etched 6H-SiC surfaces

We have performed low energy cathodoluminescence spectroscopy (CLS) measurements of localized states near 6H-SiC (0001) and (000 (1) over bar) surfaces under ultrahigh vacuum (UHV) conditions and with varying depth sensitivities. CLS reveals several electronic states deep within the SiC band gap at least two of which exhibit strong surface-dependent properties. HF etched C and Si surfaces yielded pronounced emission from near band edge transitions and also from transitions involving a set of deep levels with substantial emission intensity only a few tens of nanometers from the free surface. Lower incident beam voltages result in excitation only a few tens of nanometers from the surface and a dramatic appearance of new peaks in CLS spectra reveal a dramatic dependence of emission intensities on the excitation energy, indicating bulk-related features at 0.95 eV versus surface emissions at 1.10, 1.20, 1.35, and 1.65 eV. These measurements reveal the sensitivity of UHV-CLS techniques to localized states at SiC surfaces and their dependence on the chemical preparation used. (C) 1999 American Vacuum Society. [S0734-2101(99)07505-3].