It was noted that, although zinc oxide was a promising material for the fabrication of short wavelength optoelectronic devices, p-type doping was a step that remained challenging for the realization of diodes. Out-of-equilibrium methods such as ion implantation were expected to dope ZnO successfully, provided that the non-radiative defects introduced by implantation could be annealed out. Here, ZnO substrates were implanted with nitrogen ions, and the extended defects induced by implantation were studied by transmission electron microscopy and X-ray diffraction before and after annealing at 900C. Before annealing, these defects were identified to be dislocation loops lying either in basal planes in high N concentration regions, or in prismatic planes in low N concentration regions, together with linear dislocations. An uniaxial deformation of 0.4% along the c axis, caused by the predominant basal loops, was measured by X-ray diffraction in the implanted layer. After annealing, prismatic loops disappeared while the density of basal loops decreases and their diameter increases. Moreover, dislocation loops disappeared completely from the subsurface region. X-ray diffraction measurements showed a residual deformation of only 0.05% in the implanted and annealed layer. The fact that basal loops were favored against prismatic ones at high N concentration or high temperature was attributed to a lower stacking fault energy in these conditions. The coalescence of loops and their disappearance in the sub-surface region were ascribed to point defect diffusion. Finally, the electrical and optical properties of nitrogen-implanted ZnO were correlated with the observed structural features.

Formation and Annealing of Dislocation Loops Induced by Nitrogen Implantation of ZnO. Perillat-Merceroz, G., Gergaud, P., Marotel, P., Brochen, S., Jouneau, P.H., Feuillet, G.: Journal of Applied Physics, 2011, 109[2], 023513