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The ZnO : Ga layers were grown on the Al2O3 substrate by using the radio frequency (RF) magnetron co-sputtering system at room temperature (RT), varying the RF power of the Ga2O3 target. The RT as-grown ZnO : Ga layers were post-annealed by the rapid thermal annealing (RTA) method with various temperatures. Ga-40 of the RT as-grown ZnO : Ga layers showed an excellent crystallinity. Also, the transmittance of Ga-40 annealed at the RTA temperatures of over 300 o C was very transparent, with the transmittance exceeding 80%. Thus, the optical band-gap energy ranged from 3.4548 to 3.8118 eV according to the variation of the RTA temperature. This band-gap energy showed a tendency to increase until the RTA temperature of 400 o C, and then a decrease was observed. The lowest values of resistivity and sheet resistance were extracted from Ga-40 annealed at 400 o C; their values were 5.04 × 10−4 Ω • cm and 21.24 Ω/□, respectively. The obtained parameters were equal to those of the ZnO : Ga layer grown for maintaining the substrate temperature of 400 o C. Consequently, this result indicates that the time reduction and the simplified fabrication for device applications of the ZnO : Ga layers can be achieved through the RTA method of short-time thermal-annealing after RT growth.
