Structural evaluation of ions-implanted GaN films by photothermal deflection spectroscopy

We characterize the behavior caused by thermal annealing for C, O, Si and Mg ions implanted in GaN films by photothermal deflection spectroscopy (PDS) with respect to structural disorder and defect levels related to yellow luminescence. Although the implanted region damaged by ion bombardment is recovered by annealing, the FWHM values of ω(0002) evaluated by x-ray diffraction are almost independent of the temperature. However, the Urbach energy, as an index of structural disorder, evaluated by PDS is improved. Recovery of the structural disorder is likely to depend on the dose quantity rather than the acceleration voltage. Defect states in the band gap are reduced as well, though featured PDS signals related to the kind of implanted ion are hardly detected except for the carbon ion. The intensity of yellow luminescence at room temperature is enhanced according to the improvement of the Urbach energy and reduction of defect states in the band gap. PDS is useful for defect analysis of III-V nitride semiconductors that are electrically and optically inactive, such as ion-implantation samples, especially Mg-implanted GaN for achieving reliable p-type conduction.