A NEW LATTICE-RELAXATION MODE IN INGAAS ON GAAS

A systematic X-ray and photoluminescence (PL) investigation of lattice relaxation in InxGa1-xAs (0 < x < 0.7) thin layers grown on GaAs substrates revealed a new relaxation mode. This relaxation causes a blue shift of the PL wavelength away from the value for coherent growth. The relaxation also reduces the vertical lattice constant more than predicted by previous misfit dislocation theories. This new mode appears in a middle strain region between the relaxed region with misfit dislocations and the relaxed region with three-dimensional (3D) growth. The critical layer thickness of the InxGa1-xAs layers drops quickly due to this new mode when the strain is more than 1.8%. When the strain exceeds twice the critical strain of this new mode, the 3D growth region appears. The X-ray results suggest that the InxGa1-xAs layers interact with GaAs in this new region and that the interaction is a precursor phenomenon of the 3D growth.