Influence of [V]/[III] beam ratio on crystal qualities of GaSb-AlSb superlattice films grown by molecular-beam epitaxy

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Abstract
[V]/[III] ratio dependence of molecular-beam epitaxy (MBE) grown Ga-Al-Sb material system was studied using various kinds of characterizing methods. We found that the MBE-grown Ga-Al-Sb material (GaSb-AlSb superlattice) was very sensitive to the growth condition, especially [V]/[III] beam ratio. Deviation from an optimum value of [V]/[III] during MBE led to deterioration not only in the optical quality (drastic decrease in photoluminescence efficiency) but also in the crystallographical quality (marked increase in the full width at half maximum (FWHM) in the x-ray diffraction peak) of grown epitaxial layers. X-ray microprobe analysis (XMA) showed that the epitaxial layer having a large x-ray FWHM value does not show any deviation from the stoichiometry. X-ray diffraction showed that the layers have no fluctuation of lattice constants, and the layers are imperfect single crystals having a spread orientation of crystal axis. Rutherford backscattering measurement showed that the lattice arrangement was not regular for the sample grown under nonoptimum conditions. Raman scattering showed that even in the epitaxial layer having a large x-ray FWHM value, the superlattice structure is conserved. Transmission electron microscopic observation by different growth conditions showed different fine structures. Some discussions about growth mechanisms are given for different growth conditions.