Ion beam channelling of heteroepitaxial InGaAs layers

The strain and crystalline quality of heteroepitaxial InxGa1-xAs on GaAs substrates, nominally with x = 0.12, are measured as a function of layer thickness and substrate orientation by RBS channelling with 2.5 MeV α particles. The layers are grown by low pressure MOVPE on substrates with surfaces oriented (i) exactly on a (100) plane and (ii) misoriented by 2o from the (100) plane towards the <110> axis. Layers of thickness around the predicted critical value (particularly those on misoriented substrates) exhibit remarkably low Xmix values, indicating a high crystalline quality. The strain in each layer, measured by finding the angular displacement between the <112> axial channels of the epilayer and the substrate, shows no sign of relaxation until the thickness is many times the critical thickness. For layers which show some strain relaxation, we evaluate the concentration of misfit dislocations at the substrate/layer interface from the channelled spectra. These measurements confirm that channelling, although it provides an unambiguous measurement of layer strain, is not as sensitive as other techniques for the detection of the onset of dislocation formation. (Author)