Aluminium gallium arsenide (also Aluminum gallium arsenide) (AlxGa1-xAs) is a semiconductor with very nearly the same lattice constant as GaAs, but a larger bandgap. The x in the formula above is a number between 0 and 1 - this indicates an arbitrary alloy between GaAs and AlAs .
The bandgap varies between 1.42 eV (GaAs) and 2.16 eV (AlAs). For x < 0.4, the bandgap is direct.
The formula AlGaAs should be considered an abbreviated form of the above, rather than any particular ratio.
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