STRAIN RELAXATION IN INGAAS/GAAS QUANTUM-WELLS GROWN ON GAAS (111)A SUBSTRATES

We have grown In0.2Ga0.8As strained quantum wells (SQWs) on GaAs (111)A just and off-angled substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) peak energy of SQWs grown on (111)A related substrates shows a large redshift as compared with the calculated values. The red-shift observed in SQWs grown on a (111)A 5 degrees off toward [001] substrate can be explained by the presence of a built-in electric field E = 154 kV/cm due to piezoelectric effect. The larger red-shift observed in samples grown on the other substrates is partially due to strain relaxation. A strain relaxation mechanism that consists of coherently grown islands when InGaAs growth begins and the generation of misfit dislocations when these islands coalesce, gives a qualitative explanation of the observed results,