Wide-spectrum Mg and Ga co-doped ZnO–TCO thin films with introduced hydrogen grown by magnetron sputtering at room temperature

Abstract

• The introduction of H 2 gas improved the properties of ZnO thin films. • The formation of Mg O bond widened the band-gap of ZnO. • H atoms function as donor in the ZnO thin films. • The optical energy band gap of 3.74 eV was obtained. • The mobility of ZnO thin films can be enhanced after vacuum annealing. Transparent conductive hydrogenated Mg and Ga co-doped ZnO (HMGZO) thin films were deposited on glass substrates at room temperature by pulsed direct current magnetron sputtering, with hydrogen being introduced at various flow rates. X-ray diffraction results showed that these HMGZO thin films are polycrystalline, with a preferred (0 0 2) crystal-plane orientation. Hydrogen donors are responsible for the increase of carrier concentration and the lowest resistivity of 4.4 × 10 −3 Ω cm, with a carrier concentration of 1.92 × 10 20 cm −3 and a mobility of 7.3 cm 2 /V s, was obtained at an H 2 flow rate of 9.0 sccm. The average transmittance of the HMGZO thin films exceeded 88.6% for wavelengths of 330–1100 nm. The optical band gap ( E g ) increased from 3.41 to 3.74 eV with increasing the H 2 flow rate from 0 to 16.0 sccm. The widening of E g could be attributed both to Burstein–Moss band-filling and to incorporation of Mg atoms. The electrical stability of HMGZO thin films with post thermal annealing process was also investigated.