High-dielectric-constant Ta2O5/n-GaN metal-oxide-semiconductor structure

High-dielectric-constant Ta2O5 has been grown on the n-GaN epifilm by rf magnetron sputtering. Photoluminescence measurement has been performed to compare the luminescence intensity with and without the dielectrics. Threefold increase in intensity is obtained, and a surface recombination velocity is estimated to be 3x10(4) cm/s as an upper limit using a modified dead-layer model. A metal-oxide-semiconductor structure has been fabricated with Al on n-GaN as the ohmic contact and on Ta2O5 as the gate metal. Capacitance-versus-voltage characteristics have been measured. The doping concentration obtained from the depletion regime is compared with the result of Hall measurement, which is 7.0x10(16) cm(-3). The flat-band voltage is obtained from the high-frequency data, and the effective oxide charge number density is calculated as 4.1x10(12) cm(-2). Indication of strong inversion appears at low reverse bias due to the high dielectric constant of Ta2O5, and matches closely with calculated values. Hysteresis is observed and ascribed to positive mobile charges derived as 2.1x10(12) cm(-2). The capacitance dependence on the frequency and the leakage current are discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)01751-4].