Resistivity improvement of Al-doped ZnO film by bipolar pulsed dc magnetron sputtering with high Ar flow rate

Aluminum-doped ZnO (AZO) films were deposited on a glass substrate of 400 mm × 400 mm area by bipolar pulse dc magnetron sputtering with various Ar flow rate. The working pressure was kept at 3 mTorr by controlling pumping speed (69–1564 l/s) during the change of Ar rate from 15 sccm to 340 sccm. And the sputtering power density was 1.48 W/cm2 at 150 kHz without intentional heating of the substrate. The resistivity of films was improved from 3.2 × 10−3 Ω cm to 1.50 × 10−3 Ω cm by increasing Ar flow rate. The mobility and carrier concentration increased from 13.7 cm2/V s to 17.8 cm2/V s and from 2.29 × 1020 #/cm3 to 2.46 × 1020 #/cm3, respectively. The mobility depended on the grain size at different Ar flow rate atmosphere, regardless of the preferred orientation and type of crystal plane. And the variation of the contents inside thin film was found by AES and TPD. The average transmittance of both films was almost same in visible range, but the band gap by high flow rate deposition was improved up to 3.52 eV as compared with that by low flow rate one and pure ZnO (3.3 eV).