To improve the efficiency of GaN based power electronic devices there is tremendous and growing interest in employing metal-insulator-semiconductor (MIS) transistors. As with all compound semiconductors, there is a significant challenge in forming an electronic quality dielectric-semiconductor interface. Thus, there is a need to better understand and improve the dielectric-semiconductor interface quality in order to improve the overall performance of the device.

 

This research focuses on the benefits and properties of Al2O3, TiO2 and TiO2-Al2O3 nanolaminate thin films deposited on GaN and GaOx/GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15nm thick as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectron spectroscopy (XPS) depth profile, was lower for Al2O3/GaN than TiO2/GaN, and the nanolaminate structure did not decrease the carbon concentration. However, carbon was not detected at the interface for the GaN samples pretreated by annealing in O2 for 30 minutes at 800°C. Also, according to XPS, the Al2O3 films had a better coverage than TiO2. The RMS roughness of TiO2 and Al2O3 top layers were ~0.53nm and ~0.20nm respectively, as determined by atomic force microscopy. The dielectric constant of Al2O3 on GaOx/GaN was greatly increased compared to that of the TiO2-Al2O3 and pure Al2O3 on GaN substrate. In addition, the Al2O3 deposited on the GaOx/GaN showing no hysteresis in capacitance-voltage (C-V) characteristics, which is corresponding with a negligible carbon concentration from the XPS depth profile. These results indicate the promising potential of plasma ALD deposited Al2O3 serving as the gate oxide on GaOx/GaN based MOS devices.