Understanding the thermal evolution of defects in carbon-implanted ZnO single crystal

Defects and impurities play a major role in controlling the electrical and optical properties of semiconductor materials. Herein, hydrothermally grown ZnO single crystals have been implanted with carbon (C) dopants at room temperature and then annealed in argon atmosphere at various temperatures between 400 and 800 °C. The thermal evolution of C-related defects and their effects on the structural, optical and electrical properties of ZnO single crystals were systematically characterized and discussed. The results show ion implantation induces serious lattice disorder, and post-implantation annealing could promote the lattice renormalization, accompanied by an increase in crystal quality and average visible transmittance. Furthermore, it is found that the diffusion of octahedral carbon interstitial (C_i) along parallel to c-axis facilitates the growth of carbon sp² clusters due to its low migration barrier during annealing, which energetically contribute to the decrease of the resistivity. Meanwhile, abundant C_i will be able to enter into V_Zn to form C_Zn or combine with lattice O to form (C_O)_O donor defects upon annealing, dominating the increase of electron carrier concentration and enhancing the anomalous Raman mode at 510-525 cm^?1. These findings strengthen the fundamental understanding of the donor behavior of C impurities in ZnO.