The main objective of this thesis is to achieve an understanding of the diffusion behaviour and configuration of intentionally introduced Nickel in mono-crystalline Zinc Oxide. The diffusion of Nickel has been examined by secondary ion mass spectrometry, while Fourier transform infrared spectroscopy has been applied to inspect the configuration of the Nickel impurity. An activation energy of 4.3 eV and a pre-exponential factor of 6·10^4 cm2s−1 have been estimated for the diffusivity. It has been found that the diffusion of Nickel is strongly affected by the oxygen partial pressure, and it is suggested that both a vacancy mediated and an interstitial mechanism are involved in the transition between oxygen-rich and zinc-rich conditions. Infrared absorption lines at 4216, 4240 and 4247 cm−1 have been found to correlate with the measured concentration of Nickel, supporting the previous assignments of these lines as internal electronic transitions of substitutional Ni2+. An absorption strength of ε ≥ 1.5·10^−17 cm has been deduced for the Ni2+ defect.