Continuously graded buffers for InGaAs/GaAs structures grown on GaAs

We report on the preparation under optimized conditions and on the study of InGaAs buffers grown on GaAs, intended for MQW structures for 1.3 and 1.5 mu m optical operation at 300 K; the buffers have linear, square-root and parabolic composition profiles. They were designed so that MQWs grown atop the buffers are virtually untrained, unlike those prepared following the conventional approach that are under compressive strain. The results obtained by the concomitant use of TEM, HRXRD, AFM and PL show that, by carefully designing the buffers: (i) the misfit dislocation (MD) profiles and thicknesses of the MD-free regions in the buffers can be predetermined, (ii) active structures atop the buffers are virtually unstrained and have efficient 300 K photoluminescence in the 1.5 and 1.5 mu m windows of photonic interest, () the structures have threading dislocation concentrations in the low 10(6) cm(-2) range and show ni smooth and symmetric cross-hatchings.