Correlation between optical and transport properties of Ga-doped ZnO thin films prepared by pulsed laser deposition

Abstract

Abstract In this paper we report on the correlation between the transport and optical properties of Ga-doped ZnO films epitaxially grown on C-oriented sapphire substrates by means of pulsed laser deposition. Thin films with electron concentrations ranging between 10 20 and 10 21 cm −3 were prepared from targets containing 0.25–5 at.% Ga. The Ga content in the thin films was estimated by XPS, from the ratio between the intensities of the 2p peaks of Ga and Zn. The electron concentration in the films is very close to the Ga content for films prepared from low Ga content targets even at high deposition temperature. For Ga contents in the target larger than 1%, the Ga content in the films increases dramatically at deposition temperatures higher than 400 ∘ C while the electron concentration decreases. The optical absorption edge is shown to shift to higher photon energy with increasing electron concentration, following the Burnstein–Moss law. A systematic correlation is found between the electron mobility, as measured by the Hall effect and the broadening parameter of the optical absorption edge. Photoluminescence spectra are dominated by a near-edge broad band centered at about 3.2 eV.