Effects of annealing on donor and acceptor concentrations in Ga-doped ZnO thin films

Abstract

Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N₂, or forming-gas (5% H₂ in Ar). The donor N_D and acceptor N_A concentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with N_d = (2.8 ± 0.3) × 10²⁰cm⁻³ and N_a= (2.6 ± 0.2) × 10²⁰ cm⁻³. After annealing in Ar the samples are less compensated, with N_d= 3.7 ± 0.1 × 10²⁰ cm⁻³ and N_a= 2.0 ± 0.1 × 10²⁰ cm⁻³; furthermore, these quantities are nearly independent of thickness. However, after annealing in N₂ and forming-gas, N_D and N_A are thickness dependent, partly due to depth-dependent diffusion of N₂ and H, respectively.