The growth of highly mismatched InxGa1−xAs (0.28≤x≤1) on GaAs by molecular-beam epitaxy

Abstract

The material quality of InxGa1−xAs epilayers with 0.28≤x≤1 grown on a highly mismatched GaAs substrate and the initial growth mechanisms have been studied in detail. Cross-sectional transmission electron microscopy and double-crystal x-ray diffraction analysis of the InxGa1−xAs (x≥0.28) layers indicate that although three-dimensional island growth was found in all cases, their dislocation generation mechanisms are quite different. To study the strain relaxation process in the initial growth stage and its effects on the generation of the dislocations, 15-monolayer-thick InxGa1−xAs was grown on the GaAs. It was found that for the x=0.5 case, the thin InGaAs layer formed many small-size coherent islands; while for x=1, they changed to lower-density and much larger size relaxed islands. This shows that the growth of the highly mismatched InxGa1−xAs/GaAs heterojunction (x≥0.28) is a kinetically limited strain relaxation process. The large lattice mismatch (7.16%) between InAs and GaAs favors the early relaxation of InAs islands before they coalesce; this explains why the material quality of the InAs epilayer is better than that of InxGa1−xAs with x=0.28, 0.5, and 0.75 in spite of its larger lattice mismatch.