Abstract
Intervalley transitions induced by short-wavelength phonons in the conduction band of a superlattice (GaAs)8(AlAs)8(001) are investigated on the basis of the pseudopotential method and in the phenomenological model of interatomic forces. The main attention in the study centers around the transitions associated with the vibrations confined inside the layers. It is shown that the deformation potentials for the majority of intervalley transitions in a superlattice exceed the potentials of corresponding transitions in the binary crystals because of the localization of atomic displacements and wavefunctions of electrons inside the same layer of the superlattice.The bottom of the conduction band in (GaAs)8(AlAs)8(001) superlattice corresponds to the states Γ1(1), Z3, M1, M4 originating from sphalerite's X¯ valleys localized in AlAs layers. Transitions between them are the most intense ones and they are caused by optical vibrations of Al atoms. “Semi-interface” vibrations being mainly localized in the one side of the GaAs layer are involved in the Γ1(2)−X1, Γ1(2)−R1 and X1−Z1 transitions which are analogs of Γ¯−L¯ transitions in binaries. The transitions Γ1(2)−M1 and Γ1(2)−M4 are governed by smooth parts of wave-functions and pseudopotentials. As a consequence their intensities are comparable with those of Γ¯−X¯ sphalerite transitions in spite that these states are localized in the different layers of the superlattice.
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