Effects of film thickness and thermal treatment on the structural and opto-electronic properties of Ga-doped ZnO films deposited by sol-gel method

In this work, Ga-doped ZnO (GZO) films were prepared using the sol-gel dip coating method and the effects of film thickness (230-480 nm), heating temperature (400-600 degrees C) and atmosphere (air/argon) on the system structural and opto-electronic performances were investigated. The results show that highly c-axis oriented crystals could be easily formed in GZO coatings, which origins from a preferred nucleation and gets fully developed during the structure evolution. The increase of film thickness prolongs the sol-gel pre-heating process and promotes nucleation, resulting in a more crystalline film. Higher temperature annealing (600 degrees C) in air could degrade the Ga doping efficiency and decrease the carder concentration, but the enlarged grain size helps enhance the carder mobility and improve the film conductivity. Under the modified annealing process in argon, favorable carrier density (3.376 x 10(19) cm(-3)) and mobility (15.74 cm(2)(V s)(-1)) can be obtained at the same time, resulting a minimum film resistivity of 1.18 x 10(-2) Omega cm. The studied GZO coatings keep transparent in the visible and near infrared range, leading to high emissivity values.(>0.738). We firstly prove that the carrier concentration could play a more dominant role than its mobility in determining the thermal emittance performance of thin films. (C) 2015 Elsevier B.V. All rights reserved.