Al-Doping of ZnO Thin Films Deposited by Spray Pyrolysis

Undoped and Al-doped zinc oxide (AZO) layers, greatly transparent and with high mobility, have been prepared at low substrate temperature using a chemical reactive spray technique. The effect of aluminum incorporation in the zinc oxide (ZnO) lattice has been characterized by means of X-ray powder diffraction, Raman spectroscopy, electrical and optical measurements. AZO layers reveal a hexagonal wurtzite structure whose lattice parameter decreases with increasing Al content and whose crystal quality decreases for Al content higher than 2%. Low resistivity AZO films have been found for 3% Al content. Additionally, AZO layers exhibit a blue shift of the optical gap with the increase of Al content that is attributed to the Burstein-Moss effect due to the increase of the charge carrier concentration. A density of free electron greater than 2.0 x 10(19)cm(-3)is obtained for the AZO thin films with 5% Al. Our results encourage the use of AZO films deposited at a low temperature as electrodes and optical windows in photovoltaic devices.