Growth and characterization of co-sputtered aluminum-gallium oxide thin films on sapphire substrates

Highlights: • The effect of sputtering power on the AGO films' properties was investigated. • The bandgap values of these sputtered AGO films can reach to 4.89–5.19 eV. • XPS reveals the Ga 2p3/2 peak becomes weak by increasing the DC power of Al target. • Meanwhile, the Al 2p peak becomes strong with increasing the DC power of Al target. • AGO film (DC power: 10 W) has higher crystal quality and optimum O/(Al+Ga) ratio. Aluminum gallium oxide (AGO) films were deposited on c-plane sapphire by co-sputtering of Al and Ga₂O₃ targets at a substrate temperature of 600 °C, and then annealed at 900 °C to enhance their crystal quality. The effect of DC power (0, 5, 10, 30, 50 and 70 W) for Al target on the structural, optical and compositional characteristics of AGO films were investigated. After annealing, the films prepared at the DC powers of 0–50 W for Al target all exhibited the single crystalline structure with the (−201) plane family. The annealed film grown at the DC power of 10 W possessed the highest crystal quality than the others. With increasing the DC power from 0 to 70 W, the Al composition of AGO film increased from 0 to 6.08 at.%, while its bandgap increased from 4.89 to 5.19 eV. X-ray photoelectron spectroscopy studies indicate the intensity of Ga 2p_3/2 peak (1117.9 eV) for the AGO film decreases, whereas the intensity of Al 2p peak (74.6 eV) increases with increasing the DC power. The metal-semiconductor-metal photodetector with the annealed AGO film deposited at the DC power of 10 W possesses the largest photocurrent of 5.7 × 10⁻⁹ A and the on/off current ratio (I_on/I_off) of 1.5 × 10⁴ (@2 V and 230 nm). The better optoelectronic performance of this device was attributed that the AGO film (DC power: 10 W) had a higher crystal quality, the O/(Al+Ga) ratio close to the optimum value of 1.5. Our results present the AGO films can be successfully prepared via sputtering technique, which are highly potential for deep-ultraviolet applications.