Radiation damage formation in InP, InSb, GaAs, GaP, Ge, and Si, due to fast ions

The basic physical mechanisms of damage formation in semiconductors due to swift heavy ion (SHI) irradiation are not yet fully understood. In the present paper damage evolution and the formation of ion tracks during SHI irradiation in InP, InSb, GaAs, GaP, and Ge are investigated for irradiation with Xe or An ions having specific energies ranging from about 0.8 to 3 MeV/u. Based on these experimental results and those obtained by other authors for cluster-ion irradiation of InP, GaAs, Ge, and Si, extensive calculations were performed in the framework of the thermal spike model. As we published previously, the model was extended to correctly treat processes being specific to semiconductors. Additionally, the computer code was modified to perform calculations for cluster ions too. The calculated track radii are compared with those measured for the various irradiation conditions. Thereby, one unknown parameter in the calculations was determined by fitting one data point. With this procedure a very good agreement between calculated and measured track radii is obtained for InP, Ge, and Si irradiated under various conditions. This implies that the extended thermal spike model is well capable to explain track formation in SHI irradiated semiconductors. Furthermore, special experiments were performed, the results of which also support the thermal spike model of ion track formation and contradict competing mechanisms such as Coulomb explosion, shock waves, or lattice relaxation. Thus, visible (amorphous/heavily damaged) ion tracks occur if the electronic energy deposition per ion and unit length clearly exceeds the threshold value necessary for melting. This is possible for elemental ion irradiation of InP and InSb. In Ge and Si (and probably also in GaAs and GaP) the energy deposition necessary for melting is that high that it cannot be reached by elemental ion irradiation. Moreover, at least in InP and GaAs ion tracks can be formed also in a subthreshold irradiation regime if the material is predamaged. This suggests that the existence of point defects and clusters of point defects in the crystal lattice noticeably increases the electron-phonon coupling efficiency, resulting in a more efficient energy transfer to the lattice. Within the thermal spike model, this means that for a given electronic energy deposition in the predamaged crystal a higher temperature is reached than in the perfect one.