Identification of the Nitrogen Split Interstitial $(\mathbf{N}\mathbf{\text{−}}\mathbf{N}{)}_{\mathbf{N}}$ in GaN

Combining electron paramagnetic resonance, density functional theory, and positron annihilation spectroscopy (PAS), we identify the nitrogen interstitial defect in GaN. The isolated interstitial is unstable and transforms into a split interstitial configuration $(\mathrm{N}\mathrm{\text{−}}\mathrm{N}{)}_{\mathrm{N}}$. It is generated by particle irradiation with an introduction rate of a primary defect, pins the Fermi level at $E_C-1.0\mathrm{eV}$ for high fluences, and anneals out at $400°\mathrm{C}$. The associated defect, the nitrogen vacancy, is observed by PAS only in the initial stage of irradiation.

Figure 1

Left: $X$-band (blue, top) and $Q$-band (red, bottom) EPR spectrum at $T=4\mathrm{K}$ of the $(\mathrm{N}\mathrm{\text{−}}\mathrm{N}{)}_{\mathrm{N}}$ center and the shallow donor (SD) center for $B\parallel c$. Right: High frequency spectra (345 Ghz) for $B\parallel c$ and 20° from the hexagonal $c$ axis, $T=4\mathrm{K}$.

Figure 2

Left: $(\mathrm{N}\mathrm{\text{−}}\mathrm{N}{)}_{\mathrm{N}}$ defect concentration as a function of $p+$ fluence. Right: Ground state (bottom) and excited configuration (top), where one of the N-N dimer atoms has moved through the plane of the 3 Ga ligands (red). Defect axes (orientation of the N-N dimers, dashed lines) are also given.

Figure 3

$X$-band EPR spectrum of the $(\mathrm{N}\mathrm{\text{−}}\mathrm{N}{)}_{\mathrm{N}}$ center at $B\parallel c$ measured at $T=4\mathrm{K}$ (left) and 50 K (right) and the spectra simulated with the values given in Table .

Figure 4

Magnetization density (unpaired electron) of the neutral N split interstitial: “symmetry-free” ground state (left) and thermally averaged state with $C_{1h}$ symmetry (right).