Structural and optical characterization of type I AlSb/GaSb superlattices by means of high-resolution X-ray diffraction, X-ray reflectivity and Raman spectroscopy

Abstract

High-resolution X-ray diffraction, X-ray reflectivity and Raman techniques were employed to investigate strained AlSb/GaSb superlattices grown by molecular beam epitaxy on (0 0 1) GaSb substrates. The measured diffraction curves exhibited superlattice peaks indicative of high crystal quality. The widths of the zero and + 1 order peaks closely matched the simulated values. However, symmetrical reciprocal space maps around (004) reflection revealed the diffuse scattering components. Analysis of the “ear-like” diffuse scattering indicated a low dislocation density, typically observed at an early stage of relaxation. It was found that the AlSb layer thickness had a more significant impact on dislocation density than the GaSb thickness. In contrast, the lattice mismatch between the superlattice and the substrate had a negligible effect. X-ray reflectivity analysis demonstrated that surface roughness increased with dislocation density. Raman spectroscopy revealed the presence of GaSb-on-AlSb and AlSb-on-GaSb interfaces. The Al alloy composition in the intermediate layers between GaSb and AlSb was established. A strong dependence of the AlSb- and GaSb-LO mode positions and intensities on layer thicknesses was observed. The AlSb-LO mode shift stabilized at 8–10 ML thicknesses, while strain effects in GaSb appeared only at 4 ML. The use of X-ray diffraction and Raman spectrometry in the experiment allowed us to investigate both the structural and optical properties of the AlSb/GaSb superlattice.