Indentations have been performed on (001) faces of indium alloyed GaAs crystals in
darkness and under infrared illumination. The Vickers hardness was measured and the
dislocation microstructure around the indents observed by high voltage
transmission electron microscopy. A softening effect of indium is evidenced by
comparison with the Vickers hardness obtained in the same conditions on undoped
GaAs. No significant influence of indium on the dislocation microstructure resulting
from indentation in darkness is noted. Indentation under infrared illumination does not
reveal any macroscopic photoplastic effect; however, a modification of dislocation
microstructure is observed. Whatever the experimental conditions, dislocations appear
to experience strong lattice friction. The softening effect of indium addition and the
enhanced dislocation mobilities under infrared illumination are discussed in the
framework of dislocation glide governed by the Peierls mechanism.