Electrical and optical properties of large area Ga-doped ZnO thin films prepared by reactive plasma deposition

Abstract

Measurements of Hall effect, optical transmittance, reflectance and photoluminescence (PL) have been carried out on large area (1 m wide) polycrystalline Ga-doped ZnO (GZO) films prepared by a reactive plasma deposition (RPD) method using two plasma guns with a traveling substrate technique. Properties of films are studied with respect to both in-plane uniformity and the oxygen flow rate (OFR). A typical low-resistivity film had a resistivity of 2.8 × 1 0 − 4 Ω cm , a carrier concentration of 9.0×10 20 cm −3 and a mobility of 24 cm 2/V s, and the in-plane distribution of resistivity was within +/ −5%. The increase in OFR leads to an increase in resistivity and a decrease in the carrier concentration by nearly one decade. The optical transmittance was more than 90% in the visible region. The carrier concentration dependence of the infrared (1100–2400 nm) transmittance and the reflectance was also studied. The PL exhibited a broad near-band-edge emission, in which the above-band-gap emission is due to the non- k -conserving recombination of electrons in the degenerate conduction band with holes. The PL line shape and the PL intensity reflected the carrier concentration and non-radiative defect centers, respectively. By comparing these properties with those of small GZO films (10 cm square), we see that a successful scale-up in area has been realized with no degradation of the physical properties of films.