Pulse repetition rate dependent structural, surface morphological and optoelectronic properties of Ga-doped ZnO thin films grown by pulsed laser deposition

Abstract

Transparent conductive Ga-doped ZnO (GZO) thin films were grown on glass substrates by pulsed laser deposition using 2 at% Ga2O3 doped ZnO target. A Substrate temperature of 400 °C and oxygen pressure of 7 × 10−3 Torr was kept constant during the deposition. The effects of laser pulse repetition rate from 3 to 15 Hz on crystallographic, surface morphological, optical and electrical properties of the GZO films were investigated. All the samples show the hexagonal wurtzite phase with a dominant c-axis orientation and the optimal crystallization of the GZO film occurs at 10 Hz; which is slightly better that of the film deposited at 5 Hz. AFM and FE-SEM analysis revealed that the film growth is profoundly influenced by the pulse repetition rate and the film thickness increases with an increase in the pulse repetition rate due to enhancement in deposition rate and the island density. Hall-effect measurements confirmed that all samples are heavily doped degenerate semiconductors with n-type electrical conductivity. The electrical transport properties of the film are found to be largely dependent on the crystallinity; while their optical transmittance is majorly dominated by the film thickness and roughness. The GZO film deposited at 5 Hz shows the highest figure of merit (76.11 × 10−3/Ω) as a result of its optimum sheet resistance (3.63 Ω/□) and optical transmittance (∼88%).