Transmittance enhancement and optical band gap widening of Cu2O thin films after air annealing

Abstract

Cu2O thin films have been grown on glass substrates at room temperature by reactive magnetron sputtering. As-deposited films exhibit high electrical resistivity and low optical transmittance. To improve the film properties, post annealing treatments in air at various temperatures have been performed. Low temperature annealing (<300 °C) avoids the film oxidation into CuO and the films remain single-phased. In this temperature range, the annealing in air enhances the transmittance in the visible region due to the decrease of the defect scattering. Moreover, the optical band gap of Cu2O thin films is enlarged from 2.38 to 2.51 eV with increasing annealing temperature. The increase of optical band gap accompanying the reduction of Urbach energy indicates that the widening of optical band gap may result from the partial elimination of defect band tail after thermal annealing in air. Combining experimental results with recent reported calculations, the peak at about 1.7 eV in photoluminescence spectra is assigned to the recombination of first conduction band minimum to copper vacancy.

Electronic structures ofCu2O,Cu4O3, and CuO: A joint experiment

“…The p-type conductivity of Cu 2 O thin film has been identified by Hall effect measurements in our previous work [38]. Here, positive Seebeck coefficients of Cu 4 O 3 (+102 μV/K) and CuO (+180 μV/K) thin films have been attained, indicating p-type conductivity.…”

The Phase Evolution and Physical Properties of Binary Copper Oxide Thin Films Prepared by Reactive Magnetron Sputtering

“…The band structure of Cu 2 O, with a direct gap range from 2.1 to 2.6 eV [7,10,11,12], was experimentally well established. Although Cu 2 O has the advantage of good transparency in the visible light range, its low carrier concentration or large resistivity leads to poor performances [3,10].…”

Analysis of the Conduction Mechanism and Copper Vacancy Density in p-type Cu2O Thin Films

“…As in disordered silicon where the VBM is mainly composed of non-spherical p orbitals 9 , this creates a broad distribution of localised tail states near the VBM of Cu 2 O films. The Urbach energy ( E u ) is a parameter reflecting the width of the tail states and thin Cu 2 O films show an E u larger than the thermal energy 8, 10 . Thus, multiple carrier trapping and thermal release of holes in tail states (i.e.…”