Metallic conductivity and metal-semiconductor transition in Ga-doped ZnO

Abstract

This letter reports the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures. ${\mathrm{Zn}}_{0.95}{\mathrm{Ga}}_{0.05}\mathrm{O}$ films, deposited by pulsed laser deposition in the pressure range of $\sim {10}^{-2}\mathrm{Torr}$ of oxygen, were found to be crystalline and exhibited degeneracy at room temperature with the electrical resistivity close to $1.4\times {10}^{-4}\Omega \mathrm{cm}$ and transmittance $>80\%$ in the visible region. Temperature dependent resistivity measurements of these highly conducting and transparent films also showed, for the first time, a MST at $\sim 170\mathrm{K}$ . Mechanisms responsible for these observations are discussed in the terms of dopant addition and its effect on ionization efficiency of oxygen vacancies.