AlxGa1xN

AlxGa1-xN, commonly written as AlGaN, is a ternary III-nitride semiconductor alloy composed of aluminum nitride and gallium nitride in varying proportions. The aluminum mole fraction x ranges from 0 to 1, and the alloy crystallizes in the wurtzite structure under typical growth conditions. The bandgap is widely tunable across the ultraviolet spectrum, from about 3.4 eV for GaN (x ≈ 0) to about 6.2 eV for AlN (x ≈ 1). The composition–bandgap relationship is nonlinear, often described with a bowing parameter in the range of approximately 0.5–1.0 eV, depending on growth method and strain.

Growth and materials properties: AlGaN layers are typically grown on sapphire, silicon carbide, or GaN substrates using metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Lattice mismatch between AlGaN and substrates introduces strain and defects, particularly at high Al content. The wurtzite lattice exhibits strong spontaneous and piezoelectric polarization, creating internal electric fields that influence carrier dynamics and the optical properties of quantum wells.

Applications: The wide and tunable bandgap makes AlGaN a core material for ultraviolet optoelectronics, including deep-UV light-emitting diodes and UV photodetectors (solar-blind devices). It is also used in high-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures, where the polarization-induced two-dimensional electron gas enables high-power operation. Challenges include achieving reliable p-type doping for high-Al-content layers, managing defects from lattice mismatch, and mitigating polarization-related effects in devices.