SUPPRESSION OF DEFECT PROPAGATION IN SEMICONDUCTORS BY PSEUDOMORPHIC LAYERS

The propagation of defects in semiconductor heterostructures has been studied both theoretically and experimentally. The simple model shows that defects originating from lattice-matched regions can be prevented from entering, or can be trapped by, a pseudomorphic layer, depending on the signs of the strain induced by the defect and the strain in the pseudomorphic layer. A pseudomorphic layer can therefore prevent the defect from propagating across in and entering the critical active region of a device. Experimentally, the photoluminescence intensities of Al0.4Ga0.8As/GaAs quantum wells with and without pseudomorphic In0.2Ga0.8As layers for prevention of defect propagation have been compared. GaAs substrates of high etch pit density were used to generate defects below the quantum well and silicon implantation was used to generate defects above it. The elevated temperatures during molecular-beam-epitaxial growth and postimplant rapid thermal annealing serve to assist in defect propagation in the respective regions of the heterostructure. The structures with pseudomorphic In0.2Ga0.8As layers consistently showed much higher quantum-well photoluminescence intensities than those without the pseudomorphic layers. These results indicate smaller defect densities in the quantum wells with pseudomorphic layers and strongly support the defect propagation model.