Optically detected electron nuclear double resonance (ODENDOR) was measured in the 2.2-eV yellow luminescence band associated with a residual donor in $n$-type unintentionally doped GaN. The ODENDOR lines are due to gallium and show a quadrupole splitting that can be described with an axial tensor. The quadrupole parameter was estimated to be $\frac{q\left({}_{}{}^{69}{}_{}{}^{}\mathrm{Ga}\right)}{h}=\frac{1}{2}{Q}_{\mathrm{zz}}=0.22\mathrm{}$ MHz. A hyperfine interaction for ${}_{}{}^{69}{}_{}{}^{}\mathrm{Ga}$ of approximately 0.3 MHz for the isotropic part and of approximately 0.15 MHz for the anisotropic part was estimated from the width of the ODENDOR lines. It is tentatively suggested that Ga interstitials are residual donors.

• Received 26 August 1996

DOI:https://doi.org/10.1103/PhysRevB.54.R11042