Papers by Author: Sergey P. Tumakha

Abstract: In this study, we performed a statistical analysis of 500 Ni Schottky diodes distributed across a 2-inch, n-type 4H-SiC wafer with an epilayer grown by chemical vapor deposition. A majority of the diodes displayed ideal thermionic emission when under forward bias, whereas some diodes showed ‘double-barrier’ characteristics with a ‘knee’ in the low-voltage log I vs. V plot. X-ray topography (XRT) and polarized light microscopy (PLM) revealed no correlations between screw dislocations and micropipes and the presence of double-barrier diodes. Depth resolved cathodoluminescence (DRCLS) indicated that certain deep-level states are associated with the observed electrical variations.

Abstract: We have used depth-resolved cathodoluminescence spectroscopy (DRCLS) to correlate subsurface deep level emissions and double barrier current-voltage (I-V) characteristics across an array of Ni/4H-SiC diodes on the same epitaxial wafer. These results demonstrate not only a correspondence between these optical features and measured barrier heights, but they also suggest that such states may limit the range of SB heights in general. DRCLS of near-ideal diodes show a broad 2.45 eV emission at common to all diode areas and associated with either impurities or inclusions. Strongly non-ideal diodes exhibit additional defect emissions at 2.2 and 2.65 eV. On the other hand, there is no correlation between the appearance of morphological defects observed by polarized light microscopy or X-ray topography and the presence of double barrier characteristics. The DRCLS observations of defect level transitions that correlate with non-ideal Schottky barriers suggest that these sub-surface defect features can be used to predict Schottky barrier behavior.

Abstract: We have used depth-resolved cathodoluminescence and Auger electron spectroscopies, DRCLS and AES, respectively, to probe the electronic structure and the composition of Ti/Al ohmic contacts to p-type SiC on a nanometer scale. A continuous Ti-Si-C compound layer was observed using the Auger depth profile. No interfacial Al segregation was found. The secondary electron threshold technique showed a continuous decrease in work function from the p-type SiC to the Ti-Si-C compound layer. Our results support an ohmic contact mechanism by an intermediate semiconductor layer which reduces the otherwise large interfacial Schottky barrier height. DRCLS revealed a ~2.78 eV sub-band gap transition enhanced by interfacial reaction in the near-interface SiC, suggesting the formation of additional C or Si vacancies.