GaAlAs

GaAlAs, or gallium aluminum arsenide, refers to the family of III-V semiconductors with the formula Ga1−xAlxAs, where x ranges from 0 to 1. It is used to tailor the bandgap and refractive index for optoelectronic and high-speed electronic devices. The bandgap increases with aluminum content, ranging from about 1.42 eV at x = 0 (GaAs) to around 2.16–2.2 eV near x = 1 (AlAs). The alloy is typically direct-bandgap for low to moderate Al content (roughly x ≤ 0.4–0.5); at higher Al content the conduction-band minimum can shift from the Γ to the X point, yielding indirect gaps and reduced light emission efficiency. The lattice constant varies only slightly with composition, enabling lattice-matched layers on GaAs substrates at specific compositions.

GaAlAs is grown by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD) on GaAs or on graded buffers. It is commonly used in GaAs-based heterostructures, where AlGaAs forms wide-bandgap barriers to confine electrons and holes in GaAs quantum wells. This arrangement underpins many devices, including laser diodes, light-emitting diodes, photodetectors, and high-speed transistors such as AlGaAs/GaAs HEMTs, as well as distributed Bragg reflector structures in VCSELs.

Aluminum-containing layers are more chemically active and oxidize readily, so surface passivation and careful processing are important for device stability.