Epitaxial (GaAs)1−x(Si2)x metastable alloys on GaAs(001) and (GaAs)1−x(Si2)x /GaAs strained-layer superlattices: Crystal growth, spinodal decomposition, and antiphase domains

Abstract

The microstructure of single-crystal zincblende-structure (GaAs)1−x(Si2)x metastable semiconducting alloys with 0≤x≤0.40 has been investigated using triple-crystal x-ray diffraction (XRD), plan-view and cross-sectional transmission electron microscopy (TEM and XTEM), scanning transmission electron microscopy, and convergent-beam electron diffraction. The alloys, typically 1–3 μm thick, were grown using a hybrid sputter-deposition/evaporation technique on As-stabilized GaAs(001) and (GaAs)1−x(Si2)x/GaAs(001) strained-layer superlattices, (SLS). Alloy XRD peak widths were approximately equal to those of the GaAs substrates, 30 arcsec, and lattice constants, uncorrected for strain, obeyed Vegard’s ‘‘law’’ and decreased linearly with increasing x. TEM and XTEM examinations of (GaAs)1−x(Si2)x alloys with 0≤x≤0.20 grown on GaAs revealed no evidence of dislocations or other extended defects. Film/substrate lattice misfit strain in alloys with 0.11<x<0.20 was partially accommodated by the formation of a thin interfacial spinodal layer whose average thickness increased with x to ≂70 nm. The spinodal region, which remained epitaxial, consisted of lenticular platelets extending along the [001] direction with a compositional modulation in orthogonal directions. Films with x≥0.20 exhibited, together with the interfacial zones, inhomogeneously distributed a0/2〈110〉-type threading dislocations. Antiphase domains were observed in alloys with x≥0.23. The use of (GaAs)1−x(Si2)x/GaAs SLS buffer layers extended the composition range to x=0.3 over which dislocation-free alloys, with no evidence of interfacial spinodal decomposition, could be obtained.