Low-Threshold Stimulated Emission in ZnO Thin Films Grown by Atomic Layer Deposition

In this study, high-quality ZnO thin films were grown on sapphire substrates by atomic layer deposition (ALD), followed by high-temperature postdeposition annealing. A thin Al₂O₃ layer was subsequently deposited by ALD on the ZnO surface to reduce detrimental surface states. Photoluminescence measurements conducted in a backscattering configuration at room temperature show that the ZnO film exhibited stimulated emission with a low threshold intensity of 35.1 kW/ cm². This may be attributed to the high-quality ZnO film and Al₂O₃ surface passivation layer grown by ALD, as well as the Al doping effect caused by the thermal diffusion of Al from the sapphire into the ZnO. Results show that ZnO films grown by the ALD technique are applicable to next-generation short-wavelength photonic devices.