The Impact of Surface Defects on SiC Schottky and Ohmic Contact Formation
Silicon carbide is a leading semiconductor for high power, high temperature electronics, yet SiC devices still face problems of electrical contact control and reproducibility. Recent work worldwide shows that point and extended defects in SiC as well as chemical reactions at metal-SiC interfaces can influence contact transport properties. Yet Schottky barrier and ohmic contact formation at the intimate metal-SiC junction are relatively unexplored on the microscopic level. We have used depth-resolved cathodoluminescence spectroscopy (DRCLS) and Auger electron spectroscopy (AES) to measure the optical emissions of defects near 4H-SiC surfaces and metallized interfaces on a nanometer scale. These techniques reveal that a variety of metals on clean 4H-SiC surfaces in ultrahigh vacuum (UHV) promote the formation of mid-gap defects extending only nanometers away from the junction. These states vary in their ranges of depth and depend sensitively on interface reactivity and subsequent UHV annealing
Recombination-enhanced extension of stacking faults in 4H-SiC p-i-n diodes under forward bias
The extension of stacking faults in a forward-biased 4H-SiC PiN diodes by the recombination-enhanced motion of leading partial dislocations has been investigated by the technique of optical emission microscopy. From the temperature dependence of the measured velocity of the partials, an activation energy of 0.27 eV is obtained. Based on this and analysis of the emission spectra, a radiative recombination level of 2.8 eV for the stacking fault, and two energy levels for the partial dislocation, a radiative one at 1.8 eV and a nonradiative at 2.2 eV, have been determined.
Chemically dependent traps and polytypes at Pt'Ti contacts to 4H and 6H-SiC
We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy and x-ray photoemission spectroscopy (XPS) to probe deep level defect states at interfaces of 4H and 6H–SiC with Ti/Pt metallization. These studies aim to identify process conditions under which thermally stable ohmic and Schottky contacts can be obtained on SiC while minimizing the formation of deep level electronic states. Depth-dependent LEEN measurements establish the presence of localized states and their spatial distribution on a nanometer scale. Spectra from the near interface region of 6H–SiC indicate the existence of a SiC polytype with a higher band gap of ∼3.4 eV. Excitation of the intimate metal–SiC interface reveals a process-dependent discrete state deep within the SiC band gap. XPS measurements reveal consistent differences in the C 1s chemical bonding changes with specific process steps. Analogous chemical treatments of 4H–SiC also produce a lower band gap SiC polytype with ∼2.5 eV energy extending tens of nanome...