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

This letter reports the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures. Zn0.95Ga0.05O films, deposited by pulsed laser deposition in the pressure range of ∼10−2Torr of oxygen, were found to be crystalline and exhibited degeneracy at room temperature with the electrical resistivity close to 1.4×10−4Ωcm 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 ∼170K. Mechanisms responsible for these observations are discussed in the terms of dopant addition and its effect on ionization efficiency of oxygen vacancies.