The conduction band structure of Ga1−xAlxAs alloys from Hall mobility measurements at high pressures

Abstract

The Hall mobility of electrons in liquid-phase epitaxial Ga1–xAlxAs for alloy compositions in the range 0[sdot]23 ≤ x ≤ 0[sdot]79 has been measured as a function of hydrostatic pressure. The measurements have provided information about the relative positions of the Γ and L conduction band minima across the system, and the scattering processes. The energy separation ΔEΓL between the Γ and L minima has been found to vary with the alloy composition according to the equation ΔEΓL = (0[sdot]280—0[sdot]595x) eV. The alloy composition at which these minima are equal in energy is therefore given by x = 0[sdot]47. The implications of such a model on the conduction-band structure of GaAs are discussed. It is shown that non-equivalent inter-valley scattering redueos the electron mobilities in the Γ, L and X minima, which show a minimum in the measured Hall mobility near the pressure corresponding to the T–L crossover. The composition dependence of the electron mobility in the X minima has been derived, which also shows a minimum at x ∽ 0[sdot]47 due to disorder scattering. The electron mobility in Ga1–xAlxAs is therefore reduced due to both the disorder and non-equivalent intervalley scatterings. The strength of the non-equivalent intervalley scattering is found to depend strongly on the alloy composition.