Discontinuous tracks in relaxed SiGe alloy layers: Formation and thermal evolution

Strain-relaxed epitaxial Si1−xGex alloy layers partially doped with arsenic were irradiated with U238 ions of energy 0.8-2.7 GeV in the electronic stopping regime. Using transmission electron microscopy, clear evidence is found that in some of the Si1−xGex alloy layers latent tracks are created. Depending on the composition of the Si1−xGex alloy and on the doping level of As, the tracks exhibit a more or less discontinuous character. Larger GeAs precipitations are observed in supersaturated alloy layers. We also find indications that the velocity of the projectile ions plays an important role. Additional thermal treatment results in gradual annealing of track-related defects at low temperature (200-400 °C) and in the formation of GeAs precipitates at high (850 °C) temperature.