Preparation of Crack-Free Al_xGa_1-xN Films with High Al Composition for Schottky-Type UV Detectors

High-quality Al_xGa_1-xN layers with an Al composition of x=∼0.4 were prepared on a GaN/sapphire substrate by a combination of controlling the growth kinetics, resulting in a slow growth rate of 5 nm/min, and introducing a stress-compensating thin AlGaN interlayer between the Al _xGa_1-xN and GaN layers. To control the growth kinetic activity, the reactor pressure, TMAl/TMGa flow rate, and H₂/NH ₃ flow rate were all adjusted to obtain lessdefective and homogeneous Al_xGa_1-xN layers with high Al compositions, and optimized at a reactor pressure of 50 torr, TMAl/TMGa flow rate of 70/40 μmol/min, and H₂/NH₃ flow rate of 6/6 slpm. As a result, the sequential growth of an Al_xGa_1-xN layer on a 10-nm-thick AlGaN interlayer grown at 700°C on a 2.0-μm-thick GaN layer finally produced a crack- free, less defective, homogeneous Al _0.33Ga_0.67N film with 0.5 μm thickness. Thereafter, a typical Schottky diode of Pt/Al_0.33Ga_0.67N/LT-AlGaN interlayer/n⁺-GaN exhibited a promising electro-optical sensitivity, including a reverse leakage current of 1 nA at -5 V, UV- visible extinction ratio of ∼10⁴, and responsivity of 150 mA/W at a radiation wavelength of 280 nm.