UBC Theses and Dissertations
Dislocations in gallium arsenide deformed at high temperatures Gallagher, Patrick John
Test pieces of GaAs were cut from Czochralski grown <100> wafers. Prior to deformation the dislocation configuration was established by cathodoluminescence (CL). Etch pits produced by molten KOH on examined crystal surfaces coincided with the CL images. The test pieces were capped with Si₃N₄, heated to between 950 and 1050°C, and plastically deformed by bending. The dislocation configuration after bending was then compared to that of the undeformed crystal. It was observed that heating to 1050°C did not significantly change the as grown cellular dislocation arrays in the crystal. With strain the dislocation configuration changed appreciably. New bands of dislocations were formed, parallel to the bend axis with dislocation free regions between them. Increasing the strain increased the number of bands. Observations were made on undoped crystals with high and low dislocation densities, and Si doped crystals. The luminescent properties of the dislocations were observed to change with heating and strain. As grown, a dislocation imaged as a dark spot surrounded by a bright halo, giving bright dislocation networks. After heating to 950°C samples showed only the dark spots without halos. After deformation, all the new dislocations appeared as dark spots or lines without halos. At very low strains, the original dislocations were still evident but were distinct from the new arrays. In an attempt to correlate the dislocation images with impurity segregation some observations of the samples were made using secondary ion mass spectroscopy (SIMS). The results suggest the possibility of the dark areas in the CL images being associated with the presence of carbon.