Application of ‘‘critical compositional difference’’ concept to the growth of low dislocation density (<104/cm2) InxGa1−xAs (x≤0.5) on GaAs

Abstract

Multilayer epitaxial structures consisting of InxGa1−xAs layers of various compositions were grown on GaAs substrates by the molecular beam epitaxy technique. Dislocation evolution and residual strain in these heterostructures were studied using cross-sectional transmission electron microscopy (XTEM) and high-resolution x-ray diffraction analyses, respectively. The multilayer heterostructures were designed such that the compositional difference between two adjacent InxGa1−xAs layers in the stack was less than a critical compositional difference of Δx=0.18, taking partial lattice-relaxation into account. XTEM studies of the stacked structures indicated dislocation evolution to be confined to the GaAs substrate and the InxGa1−xAs layers underlying the top InxGa1−xAs layer in the stack, the top InxGa1−xAs layer being essentially dislocation-free. This phenomenon is attributed to a monotonic increase in the yield strength of InxGa1−xAs at the appropriate growth temperatures with increasing values of x. Such behavior appears to persist up to an InxGa1−xAs composition of approximately x=0.5, whereupon a further increase in composition results in dislocation evolution in the top layer of the stack. It is postulated that the yield strength of InxGa1−xAs decreases with increasing values of x beyond x=0.5. Extremely low dislocation density InxGa1−xAs material was grown on GaAs using the stacked structure approach as evidenced by etch pit analysis. For example, dislocation densities of 1–2×103/cm2 and 5–6×103/cm2 were recorded from In0.35Ga0.65As and In0.48Ga0.52As top layers, respectively. Such InxGa1−xAs alloys would be potentially suitable for the fabrication of photonic devices operating at 1.3 μm (x=0.35) and 1.55 μm (x=0.48).