The growth and investigation on Ga-doped ZnO single crystals with high thermal stability and high carrier mobility

Abstract

ZnO:Ga (GZO) materials with high thermal stability and high carrier mobility are essential for the development of transparent conductive electrodes (TCE). Theoretically, only the substitution doping of Ga could result in the main donor with very high thermal stability. For achieving this goal, we adopted a hydrothermal method to acquire GZO single crystals, based on the fact that the hydrothermal method can possibly provide an approximate thermodynamic equilibrium growth environment to grow GZO materials with perfect substitution of Ga for Zn. A centimetre-sized GZO single crystal with Ga dosage amount of 0.053 wt% (2.19 × 10¹⁹ cm⁻³) was grown by the hydrothermal method. A precise measurement of the lattice constants reveals that the cell volume of the GZO crystal slightly shrinks by 0.09% after doping with Ga, indicating that the Ga atoms have substituted for Zn atoms, instead of existing as interstitial sites to expand the lattice parameters. A sharp X-ray rocking curve with the full width at half-maximum of the (002) reflection around 46.4 arc sec shows the high crystallinity of the GZO crystal. As expected, the as-grown GZO crystal exhibits a high RT carrier concentration (1.07 × 10¹⁹ cm⁻³) and the highest value of Hall mobility (81.5 cm²/(V s)) among current GZO materials. High thermal-stability is indicated by the little variation of these two parameters after being annealed at 1100 °C for 24 h. The carrier concentration is nearly independent of temperature (77–300 K).