Characteristics of Gallium and Aluminum Co-doped ZnO (GAZO) Transparent Thin Films Deposited by Using the PLD Process

Transparent conducting GAZO (Ga and Al co-doped zinc oxide) thin films were deposited at various combined Ga and Al doping concentrations and substrate temperatures by using a pulsed laser deposition (PLD) process. The crystal structures and the electrical and optical properties of GAZO films were analyzed using X-ray diffraction, Hall effect tester, atomic force microscopy, and UV-visual spectrometry measurements. The GAZO thin films doped with 1.5 at% of Ga/Al showed the lowest electrical resistivity of 2.18 x 10(-4) Omega cm, an electron concentration of 9.4 x 10(20)/cm(3), a carrier mobility of 28.4 cm(2)/Vs, and an average optical transmittance of 85% when the processing parameters were optimized We found that GAZO thin films began to crystallize at 150 degrees C and that a well-crystallized phase could be obtained at a substrate temperature 300 degrees C. As the doping concentration was increased, the optical absorption edge shifted toward high photon energy. The optical band gap energy calculated from the transmittance data increased from 3.50 eV to 3.74 eV as the doping concentration was increased from 0.5 at% to 2 at%.