Growth And Characterization Of GaAs/AlAs Superlattice Alloys

Recent studies of short period GaAs/AlAs superlattices grown by molecular beam epitaxy have shown that the superlattice bandstructure resembles that of the AlCaAs alloy system. We have studied indirect gap GaAs/AlAs superlattice alloys using x-ray diffraction and pressure dependent magneto-luminescence. Analysis of the x-ray data shows that the AlAs layers are strained to be pseudomorphic with the GaAs substrate. Because the indirect conduction band ground state derives from the AlAs X-point these superlattice alloys must be treated as strained-layer superlattices. Interpretation of luminescence data using Kronig-Penney and tight-binding analyses of the superlattice bandstructure and optical dipole matrix elements shows that this experiment provides a sensitive measure of the conduction band offset for the GaAs/AlAs system. Quantum size effects lift the three-fold degeneracy of the X-point to yield an in-plane X band quantized according to the transverse electron mass (Xt) and a separate X band along the superlattice axis quantized according to the longitudinh electron mass (X1). Strain shifts at the X-points are of the same magnitude as quantum size effect shiffs and drive the Xt band toward lower energies. The effect of strain in the conduction band can be acdurately modeled by assuming GaP deformation potentials for the AlAs layers.

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