AlGaN

Aluminum gallium nitride (AlGaN) is a ternary III-nitride semiconductor alloy formed by varying the aluminum content in GaN and AlN. By adjusting the composition x in AlxGa1−xN, the bandgap can be tuned from about 3.4 eV for GaN to roughly 6.2 eV for AlN at room temperature, enabling devices that operate in the deep ultraviolet (UV) to near-UV range. The alloy generally preserves the wurtzite crystal structure, though increasing aluminum content raises lattice mismatch with common substrates, affecting material quality.

Key properties include a wide direct bandgap, high breakdown fields, and strong spontaneous and piezoelectric polarization. The polarization difference at AlGaN/GaN interfaces creates a two-dimensional electron gas in heterostructures, a feature exploited to fabricate high-electron-mobility transistors (HEMTs) used in high-frequency and high-power electronics.

Growth and fabrication methods commonly employed are metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), with hydride vapor phase epitaxy (HVPE) used for certain layer structures. Substrates include sapphire (Al2O3), silicon carbide (SiC), and GaN templates to mitigate defects and accommodate strain. Epitaxial strategies often involve graded or step-graded buffers to manage lattice mismatch and dislocations.

Applications of AlGaN span UV optoelectronics and electronics. Deep-UV light-emitting diodes and laser diodes benefit from the large bandgap, while UV photodetectors and solar-blind sensors take advantage of short-wavelength absorption. In electronics, AlGaN/GaN heterostructures enable robust power electronics and RF transistors. Challenges remain in achieving uniform high-Al-content layers and controlling defects during growth.