Investigation of defects in Gd doped GaN using thermally stimulated current spectroscopy

Defects in Gd-doped GaN layers are investigated using thermally stimulated current spectroscopy (TSC). The line-shape function, which commonly considers a delta function like density of state for the trap levels, is modified to take into account broad trap distributions. This function is used to fit the spectra which show two broad TSC features in all Gd-doped samples. The feature associated with the trap distribution peaking at about 45 meV from the band edge (TSC-1) can be attributed to unintentional oxygen donors, while the second feature for which the distribution peaks at ≈130meV (TSC-2) from the band edge is assigned to the defects resulting due to Gd incorporation as the intensity of this feature increases with the Gd concentration. However, only a portion of the TSC-2 band, which is estimated to have an activation energy of 240 meV, is substantially reduced upon annealing at 800 °C. The annealing also results in a complete suppression of the magnetization. This implies that the observed magnetization is likely to be resulting from the defects associated with this portion of TSC-2 band. Furthermore, the energetic position of this portion of TSC-2 band (240 meV) matches very well with the activation energy (≈200meV) for the low temperature PL peak at 3.05 eV, which has already been attributed to the defects responsible for the observed magnetic behavior. This suggests that both the TSC and the PL features are resulting from the same defect type and therefore, could provide a vital clue in the search for the exact nature of the defect responsible.