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

High-dielectric-constant Ta2O5 has been grown on the n-GaN epifilm by rf ma gnetron sputtering. Photoluminescence measurement has been performed to com pare 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 o n n-GaN as the ohmic contact and on Ta2O5 as the gate metal. Capacitance-ve rsus-voltage characteristics have been measured. The doping concentration o btained from the depletion regime is compared with the result of Hall measu rement, 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 c alculated as 4.1x10(12) cm(-2). Indication of strong inversion appears at l ow reverse bias due to the high dielectric constant of Ta2O5, and matches c losely with calculated values. Hysteresis is observed and ascribed to posit ive 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].