Effect of annealing on electrical properties of radio-frequency-sputtered ZnO films

We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800-1,000 degrees C. The electron concentration increased with annealing temperature reaching 1.4 x 10(19) cm(-3) for 1,000 degrees C. Mobility also increased, however, reaching its maximum value 64.4 cm(2)/V. sec for 950 degrees C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 angstrom). After annealing at 900 degrees C, the leakage current (at -5 V reverse bias) decreased from 2.2 x 10(-7) A to similar to 5.0 x 10(-8) A after annealing at 900 C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950 C. The leakage current decreased from 2.0 x 10(-4) A to 3.0 x 10(-7) A at -10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at; 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher.