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Negative thermal quenching (NTQ) was observed in bound exciton emission line in undoped ZnO and the donor-to-valence-band emission in heavily Gadoped ZnO thin films grown on c-Al 2 O 3 (1000) through low temperature photoluminescence spectra. In both cases, the enhanced feature of PL peak intensity occurred in the temperature range of 35-45 K corresponding to the energies of either excitation to the vibrational/rotational resonance states or the involvement of B-valence band considering the activation energy of about 5 meV.

We present the results of Ti/Ni/Ti/Au multilayer ohmic contacts on n-type 6H-SiC and their interface analysis. The as-deposited contacts show rectifying behavior and, with the increase in annealing temperature, they gradually transform to high-quality ohmic contacts exhibiting linear current-voltage characteristics. The interface evolution was analyzed through glancing angle X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy. The TiSi 2 and Ni 2 Si formed at the interfaces during the low-temperature annealing initiate the conversion from Schottky to ohmic behavior, while the increased Ni 2 Si formation at high-temperature annealing makes the perfect ohmic contacts. The results were interpreted through the thermodynamic reaction mechanisms.