Rosette Microstructure in Indented (001) GaAs Single Crystals and the a /b Asymmetry

The characteristic features of the dislocation microstructure that develops around indentations performed at room temperature on (001) GaAs single crystals are analysed by High Voltage Transmission Electron Microscopy. It is shown that perfect rosette dislocations (with Burgers vector parallel to the surface) are nucleated deeply in the crystal and never merge at the sample surface. Perpendicular rosette arms have similar lengths, which raises the question of the a/b asymmetry. Twins are present in one rosette arm only; twinning dislocations are nucleated on ± or very close to ± the indented surface. These results are discussed in connection with previously reported results.