71Ga NMR characterization of an n-doped free-standing gallium nitride wafer

Abstract

The crystallinity of an n-doped free-standing GaN wafer sliced from a GaN crystal grown on a GaN template with a mask pattern was characterized by 71Ga NMR. The quadrupolar frequency determined from the quadrupolar-split 71Ga spectra agreed with that of free-standing GaN single crystals reported in the literature. On the other hand, the broad satellite transition lines compared to the central transition line manifested structural deviation. The satellite linewidths were notably anisotropic with respect to the angle between the magnetic field and the crystalline axes; this phenomenon was attributed to the strain distribution inside the crystal. Assuming uniform deformation of the crystal as the main origin of the satellite linewidths, the longitudinal strain distribution was estimated to be on the order of 10−5. The strain distribution was also found to be slightly larger at the center of the wafer than at the edge.