DISLOCATIONS IN MEDIUM TO HIGHLY MISMATCHED III-V EPITAXIAL HETEROSTRUCTURES

Strain induced dislocations have been studied in medium mismatched InxGa1-xAs/GaAs single layers (0.57% < f < 1.07%) and superlattice heterostructures (0.43% < f < 2.1%) and highly mismatched (f almost-equal-to 3.8%) InP/GaAs single layers. The location, propagation and nature of misfit dislocations have been investigated using electron microscopy techniques. The InGaAs/GaAs single layers were grown with different compositions and thicknesses directly onto the GaAs substrate without any GaAs buffer layers. In this case misfit dislocations were found to be confined at the heterointerface or within 150-200 nm of the interface, mostly inside the epilayer. On the contrary, a GaAs buffer layer was grown between the superlattice structures and the substrates. For 0.43% < f < 1.35 misfit dislocations were confined inside the buffer layers or at the buffer-superlattice interface, without threading the superlattice. For higher mismatch values (f = 2.1%), the superlattice presented both interfacial and threading dislocations. Asymmetric dislocation movement induced by the electron beam in a scanning electron microscope on as-grown samples, most likely associated with metastability of the superlattices, was observed when thickness and composition were such that a low linear dislocation density (< 2 x 10(3) cm-1) was present. Mainly 60-degrees type misfit dislocations were observed in all the InGaAs/GaAs structures investigated. The InP/GaAs heterostructures had a higher linear dislocation density (almost-equal-to 10(6) cm-1) and planar defects were found to thread the epilayers from the heterointerface up to the free surface. The density of these defects was found to decrease as the free surface was approached. Both 60-degrees and 90-degrees type dislocations were found in this system.