Swift heavy ion irradiation of crystalline CdTe

The influence of high electronic energy deposition in cadmium telluride (CdTe) was investigated using Rutherford backscattering spectrometry in channelling configuration as well as high-resolution transmission electron microscopy. Swift heavy ion irradiation was performed at room temperature with 185 MeV Au ions at perpendicular and non-perpendicular ion incidence. Independent of the ion incidence angle, neither ion beam induced point defects nor amorphous ion tracks were observed along the ion path. In contrast, the irradiated layer possesses a high crystalline quality even after irradiation with high ion fluences, i.e. multiple ion overlap. Nevertheless, irradiation with swift heavy ions leads to the formation of extended defects in a thin layer close to the sample surface. With increasing ion fluence the concentration of these extended defects increases continuously. This suggests that high electronic energy deposition causes the formation of defects, however, the combination of the high defect mobility within the thermal spike and the high ionicity of CdTe may benefit an effective recovery of the ionic bonds and consequently an easy recovery of the lattice, i.e. a nearly perfect recrystallization. The experimentally observed high defect resistivity enables a high doping of foreign atoms in CdTe over a wide depth range without the formation of lattice defects which is important for the use of CdTe as an effective absorber for solar cells.