Study on change of electrical properties of ZnO thin films deposited in low temperature facing targets magnetron sputtering (FTS) system with H2 and O2 flow rate changes

摘要

The optical, structural and electrical properties of ZnO thin film deposited by FTS system with H2 and O2 addition at low processing temperature were studied. The sheet resistance of the ZnO thin film increased from ～10~(-3) to ～10~6 Mohm/sq. with the O2 flow rate and decreased from ～10~(-1) to ～10~(-4) Mohm/sq. with the H2 flow rate increase. The increase of sheet resistance with O2 flow rates could be explained by oxygen vacancies. The decrease of sheet resistance with H2 flow rates could be explained by increase of the electrons from interstitial hydrogen atoms. The electrical property showed dramatic change with the small change of the flow rates. Conversely, the optical and structural characteristics did not show large variation. According to H2 and O2 flow rate change, transmittance of the deposited ZnO thin film varied in the range of 84 ～ 87% while the optical band gap showed small shift to the range of 3.22 eV～3.26 eV. XRD measurements showed that the deposited ZnO thin film was composed of amorphous and crystalline phase and the grain size varied in the range of 15.37 ～ 17.89 with the flow rate change of H2 and O2. The plasma characteristics were analyzed using optical emission spectroscopy (OES) but the overall spectrum did not change with the H2 and O2 gas flow rates. Therefore, the dramatic changes in the electrical properties of ZnO thin films could be attributed to change in chemical composition of the thin films rather than the plasma status.