Growth of Ga-doped ZnO bilayer by RF magnetron sputtering with different atmospheres

Influence of substrate temperature and atmosphere on the electrical and optical properties of Ga-doped ZnO thin films deposited by rf magnetron sputtering were investigated. The electrical resistivity of Ga-doped ZnO (GZO) films decreases first and then increases as the substrate temperature increases from room temperature to 400 degrees C. A minimum resistivity of 3.3 x 10(4) Omega CM is obtained at 300 degrees C. The resistivity nearly does not change with the O-2/Ar flow ratio, R for R < 0.25 but increases rapidly with R for R > 0.25. Changes in resistivity with the substrate temperature and R are related to the crystallinity of GZO films. The crystallinity is enhanced as R increases, but if the oxygen partial pressure is higher than a certain level (R = 0.25 +/- 0.10) gallium oxides precipitate at grain boundaries, which decrease both carrier concentration and mobility. Optical transmittance increases as R increases for R < 0.75. This change in transmittance with R is related to changes in oxygen vacancy concentration and surface roughness with R.