aAlxGa1xAs

AlxGa1−xAs, commonly written AlGaAs, is a ternary III–V semiconductor alloy formed from aluminum arsenide (AlAs) and gallium arsenide (GaAs). The composition is specified by x, with 0 ≤ x ≤ 1, giving the formula AlxGa1−xAs. By adjusting x, the material’s electronic and optical properties can be tuned across a wide range.

The alloy shares the zinc blende crystal structure with GaAs and AlAs. The lattice constant a(x) follows Vegard’s law, a(x) ≈ (1−x)a_GaAs + x a_AlAs, where a_GaAs ≈ 5.653 Å and a_AlAs ≈ 5.661 Å. Consequently, a(x) increases slightly with x. For small aluminum content, AlGaAs is nearly lattice matched to GaAs, which is advantageous for growing high-quality heterostructures on GaAs substrates.

The bandgap energy Eg(x) increases with aluminum content, spanning roughly 1.42 eV for GaAs to about 2.16 eV for AlAs at room temperature. The dependence is non-linear and often described with a bowing parameter. AlGaAs is a direct-bandgap material for low x (approximately x less than 0.45) and tends toward an indirect gap as x increases beyond this range, due to a shift of the conduction-band minimum from the Gamma to the X point.

Growth and applications: AlGaAs is grown by molecular beam epitaxy or metal-organic chemical vapor deposition on GaAs substrates. It is widely used in optoelectronic and high-speed devices, including laser diodes, LEDs, waveguides, photodetectors, and GaAs/AlGaAs quantum wells and related heterostructures, where its tunable bandgap and lattice compatibility are essential.