A comparative study was made of the relaxation of thin single InxGa1-xAs/GaAs quantum wells which had been grown simultaneously onto (001) and (111)B GaAs substrates. Transmission electron microscopy indicated that the primary relaxation mechanism in high-In (001) samples was the formation of 3-dimensional islands. Under the present conditions, this occurred at In contents above 0.24. Although they were initially coherent with the substrate, catastrophic relaxation occurred above a critical thickness, due to a very high (above 1012/cm2) density of edge dislocations, as the islands coalesced. No similar relaxation mechanism was observed for the (111) orientation. Three-dimensional islanding was suppressed there and, instead, a novel configuration of misfit dislocations appeared at x-values above 0.24. This new configuration represented an additional misfit-relieving component which had not been taken into account in previous theoretical analyses of the critical layer thickness for (111)B. On the other hand, this mechanism was relatively inefficient when compared to the catastrophic relaxation, and the (111)B substrate still offered considerable advantages.

Relaxation Study of InGaAs/GaAs Quantum-Well Structures Grown by MBE on (001) and (111)B GaAs for Long Wavelength Applications J.J.Sánchez, J.M.G.Izpura, J.L.Sánchez-Rojas, M.Hopkinson, M.Gutiérrez, D.González, G.Aragón, R.García: Journal of Crystal Growth, 1999, 206[4], 287-93