Relaxed, high-quality InP on GaAs by using InGaAs and InGaP graded buffers to avoid phase separation

Abstract

Using compositionally graded buffers, we demonstrate InP on GaAs suitable for minority carrier devices, exhibiting a threading dislocation density of 1.2×106∕cm2 determined by plan-view transmission electron microscopy. To further quantify the quality of this InP on GaAs, a photoluminescence (PL) structure was grown to compare the InP on graded buffer quality to bulk InP. Comparable room and low temperature (20K) PL was attained. (The intensity from the PL structure grown on the InP on GaAs was ∼70% of that on bulk InP at both temperatures.) To achieve this, graded buffers in the InGaAs, InGaP, InAlAs, and InGaAlAs materials systems were explored. In each of these systems, under certain growth conditions, microscopic compositional inhomogeneities blocked dislocation glide and led to threading dislocation densities sometimes >109∕cm2. These composition variations are caused by surface-driven, phase separated, Ga-rich regions. As the phase separation blocked dislocation glide and led to high threading dislocation densities, conditions for avoiding phase separation were explored and identified. Composition variations could be prevented in InxGa1−xAs graded buffers grown at 725°C to yield low dislocation densities of 9×105∕cm2 for x<0.34, accommodating ∼70% of the lattice mismatch between GaAs and InP. Compositional grading in the InyGa1−yP (0.8<y<1.0) materials system grown at 700°C was found to accommodate the remaining lattice mismatch to achieve high-quality InP on GaAs with little rise in threading dislocation density by avoiding phase separation.