Alloy-disorder-induced intervalley coupling

The intervalley coupling between Γ and X minima of the conduction band is investigated in highly excited ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As. The efficiency of indirect electron-hole recombination as a function of hydrostatic pressure directly yields the relative strength of alloy-disorder and phonon-assisted intervalley scattering for both GaAs-like and AlAs-like LO phonons. Intervalley transfer assisted by alloy disorder is proved to be very efficient, with a strength of about 25% of the overall deformation-potential scattering. The zero-phonon processes dominate the carrier dynamics close to the direct-to-indirect crossover in the ternary compounds. They are always negligible in GaAs with an indirect gap under high hydrostatic pressure, which proves the attribution of the zero-phonon intervalley coupling in ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As to alloy disorder. The properties of direct recombination in indirect-gap ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As further support the existence of efficient disorder-induced Γ-X transfer.