Determination of activation behavior in annealed Al–N codoped ZnO Films

Abstract

Al–N codoped ZnO films prepared via cosputtering technology were postannealed at 450 °C for 30 min under ambient vacuum and nitrogen. The extrinsic impurities in these annealed samples, resulting in evolutions on the carriers and radiation emissions, were investigated through their photoluminescence spectra and Hall-effect measurements. It was found that the donor-acceptor-pair emission was related to the VZn–AlZn transition at 2.86 eV and predominated over the defect-transition luminescence in the room-temperature photoluminescence (RTPL) spectrum of the vacuum-annealed sample, which possessed a high electron carrier concentration. With the help of temperature-dependent Hall measurements, a shallow donor level corresponding to Al on the Zn site (AlZn) was derived as EC − (51 ± 4) meV. In contrast, the defect-transition luminescence in the RTPL spectrum of the nitrogen-annealed Al–N codoped ZnO film, showing p-type conduction with a hole concentration of 1018 cm−3, was dominated by the VO–NO deep level emission at approximately 1.87 eV. The estimated acceptor level corresponding to the N on the O site (NO) was EV + (149 ± 6) meV. The binding energy and the activation energy associated with the NO acceptor were also determined by the low-temperature photoluminescence and temperature-dependent PL spectra.