Direct evidence of impurity decoration of Ga vacancies in $\mathrm{GaN}$ from positron annihilation spectroscopy

Positron annihilation spectroscopy, supported by ab initio theory, has been applied to verify the decoration of Ga vacancies in $\mathrm{GaN}$ by oxygen and hydrogen. Our results indicate that the Doppler broadening measurement of electron momentum distribution is sensitive enough to distinguish even between N and O atoms neighboring the Ga vacancy. We identify isolated $V_{\mathrm{Ga}}$ in electron irradiated $\mathrm{GaN}$ and $V_{\mathrm{Ga}}\text{−}{\mathrm{O}}_{\mathrm{N}}$ complexes in highly O-doped high-purity $\mathrm{GaN}$. Evidence of H decoration of Ga vacancies is obtained in epitaxial $\mathrm{GaN}$ grown by metalorganic chemical-vapor deposition.

Figure 1

The average positron lifetime as a function of measuring temperature. The first number in the parentheses stands for O concentration and the second one indicates the free carrier concentration.

Figure 2

Gallium vacancy concentration as a function of doping. The solid line is a guide to the eye. The results in the sample with the lowest O concentration have been taken from Ref. 18.

Figure 3

The measured and calculated momentum distribution for an isolated Ga vacancy. Both of these curves are shown as ratios to the data obtained in the $\mathrm{GaN}$ lattice.

Figure 4

Measured and calculated momentum distribution curves for different types of samples and defects, respectively. All these curves are shown as ratios to the data obtained in the $\mathrm{GaN}$ lattice.