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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Atomic layer deposition TiO 2 -Al 2 O 3 stack: An improved gate dielectric on Ga-polar GaN metal oxide semiconductor capacitors

This research focuses on the benefits and properties of TiO 2 -Al 2 O 3 nano-stack thin films deposited on Ga 2 O 3 /GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO 2 , 7.1 nm Al 2 O 3 and 2 nm Ga 2 O 3 as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectron spectroscopy (XPS) depth profile, was negligible for GaN pretreated by thermal oxidation in O 2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO 2 -Al 2 O 3 on Ga2O3/GaN was increased to 12.5 compared to that of pure Al 2 O 3 (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 10 11 cm -2 . The gate leakage current density (J=2.81× 10 -8 A/cm 2 ) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO 2 /Al 2 O 3 for serving as the gate oxide on Ga 2 O 3 /GaN based MOS devices.

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