CONTINUOUSLY GRADED BUFFERS FOR INGAAS GAAS STRUCTURES GROWN ON GAAS/

We report on the preparation under optimized conditions and on the stu dy 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, sq uare-root and parabolic composition profiles. They were designed so th at MQWs grown atop the buffers are virtually untrained, unlike those p repared following the conventional approach that are under compressive strain. The results obtained by the concomitant use of TEM, HRXRD, AF M and PL show that, by carefully designing the buffers: (i) the misfit dislocation (MD) profiles and thicknesses of the MD-free regions in t he buffers can be predetermined, (ii) active structures atop the buffe rs are virtually unstrained and have efficient 300 K photoluminescence in the 1.5 and 1.5 mu m windows of photonic interest, () the structur es have threading dislocation concentrations in the low 10(6) cm(-2) r ange and show ni smooth and symmetric cross-hatchings.