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This study compares the physical, chemical and electrical properties of Al2O3 thin films deposited on gallium polar c- and nonpolar m -plane GaN substrates by atomic layer deposition (ALD). Correlations were sought between the film's structure, composition, and electrical properties. The thickness of the Al2O3 films was 19.2 nm as determined from a Si witness sample by spectroscopic ellipsometry. The gate dielectric was slightly aluminum-rich (Al:O=1:1.3) as measured from X-ray photoelectron spectroscopy (XPS) depth profile, and the oxide-semiconductor interface carbon concentration was lower on c -plane GaN. The oxide's surface morphology was similar on both substrates, but was smoothest on c -plane GaN as determined by atomic force microscopy (AFM). Circular capacitors (50-300 μm diameter) with Ni/Au (20/100 nm) metal contacts on top of the oxide were created by standard photolithography and e-beam evaporation methods to form metal-oxide-semiconductor capacitors (MOSCAPs). The alumina deposited on c -plane GaN showed less hysteresis (0.15 V) than on m -plane GaN (0.24 V) in capacitance-voltage (CV) characteristics, consistent with its better quality of this dielectric as evidenced by negligible carbon contamination and smooth oxide surface. These results demonstrate the promising potential of ALD Al2O3 on c -plane GaN, but further optimization of ALD is required to realize the best properties of Al2O3 on m -plane GaN. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The benefits of dry oxidation of n -GaN for the fabrication of metal-oxide-semiconductor structures are reported. GaN thin films grown on sapphire by MOCVD were thermally oxidized for 30, 45 and 60 minutes in a pure oxygen atmosphere at 850 °C to produce thin, smooth GaOx layers. The GaN sample oxidized for 30 minutes had the best properties. Its surface roughness (0.595 nm) as measured by atomic force microscopy (AFM) was the lowest. Capacitance-voltage measurements showed it had the best saturation in accumulation region and the sharpest transition from accumulation to depletion regions. Under gate voltage sweep, capacitance-voltage hysteresis was completely absent. The interface trap density was minimum (Dit = 2.75×1010 cm-2eV-1) for sample oxidized for 30 mins. These results demonstrate a high quality GaOx layer is beneficial for GaN MOSFETs. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The influence of postgrowth high-temperature anneals between 1400°C and 2400°C on the behavior of the D1 center in semi-insulating 4H-SiC was studied by photoluminescence. The optical signature of D1 was observed up to 2400°C with intensity maxima at 1700°C and 2200°C. It was also found that changes in the postannealing cooling rate drastically influence the behavior of the D1 center and the concentrations of the VC, VSi, VC–VSi, and VC–CSi lattice defects observed from electron paramagnetic resonance experiments. The change in intensity of the D1 defect has some correlation with the intensity change of the VC–VSi pair defect at temperatures above 1900°C. In addition, infrared photoluminescence spectroscopy studies showed that changes in the intensity of the D1 defect at 2100°C to 2400°C annealing temperatures and variable cool-down rates have close correlation with intensity changes of the UD2 defect. [ABSTRACT FROM AUTHOR]