•AlGaN growth with in situ curvature and reflectance monitoring.•High-quality n-Al0.5Ga0.5N thick film with 2D growth was realized under heavy Si doping.•The MQWs grown on the optimized n-Al0.5Ga0.5N demonstrated a high IQE.The control of stress, growth mode, and morphology in n-Al0.5Ga0.5N grown by metal-organic chemical vapor deposition (MOCVD) were systematically investigated. A 2-μm-thick completely relaxed n-Al0.5Ga0.5N was obtained by adjusting the structure of AlN/Al0.5Ga0.5N superlattices. N-Al0.5Ga0.5N showed an excellent 2D growth at a growth rate of 0.55 µm/h. An almost pit-free surface was realized by lowering the V/III ratio. Finally, the electron concentration and mobility of the optimized n-Al0.5Ga0.5N reached up to 4.2×1018 cm−3 and 48.2 cm2/(V s), respectively. The MQWs grown on the optimized n-Al0.5Ga0.5N demonstrated an outstanding internal quantum efficiency of 47% at 283 nm.

This paper presents the design for a heterojunction AlGaN solar-blind avalanche photodiode (APD) with improved noise performance. Increasing the Al composition of AlGaN in the multiplication layer from 0.40 to 0.45 was calculated to significantly reduce the excess noise factor of this heterojunction APD. The polarization electric field induced in the multiplication layer had the same direction as the applied reverse bias field, which helped lower the avalanche breakdown voltage. The calculated results demonstrated that the apparent spike in the electric field intensity at the i-Al0.4Ga0.6N/n-Al0.5Ga0.5N interface can be effectively suppressed by inserting a grading n-AlGaN layer, which helps reduce the dark current.

Dry thermal oxidation of GaN thin films grown on Al2O3 (0001) has been performed at different temperatures. The oxidized samples were investigated through X-ray diffraction (XRD) and atomic force microscope (AFM). For samples oxidized at temperatures from 800 °C to 950 °C, XRD peaks from the (−201), (−402) and (−603) planes of β-Ga2O3 were observed, indicating that a β-Ga2O3 layer was formed on GaN epitaxially. The epitaxial relationships were determined to be β-Ga2O3(−201)||GaN(002) and an in-plane orientation of β-Ga2O3[010]||GaN[110]. When the oxidation temperature is increased further to 1000 °C, in addition to the peaks from the (−201), (−402) and (−603) planes, extra peaks corresponding to other planes appeared, indicating that the oxidized layer had deteriorated to polycrystalline Ga2O3.