Physical properties of tin oxide films deposited by oxidation of SnCl2

Highly transparent and conducting SnO₂ films, as required in thin film heterojunction solar cells, were deposited onto Pyrex glass substrates by oxidation of SnCl₂ in the temperature range 350–500°C. Oxygen with a flow rate of between 1 and 3.251 min^-1 was used as both the carrier gas and the oxidizing agent. For films deposited in these conditions the resistivity varies from 10^-2 to 10^-3 Ω cm with transmission in the range 87%–71%. It was observed that both the resistivity and the transmission decrease with increasing deposition temperature. The resistivity of films deposited at a fixed deposition temperature passes through a minimum as the oxygen flow rate is increased. Hence, SnO₂ films with low resistivity and high transmission can be produced by the oxidation of SnCl₂ at relatively low temperatures using the oxygen flow rate corresponding to the minimum resistivity. For example, in the present work, low resistivity (4.4 × 10^-3 Ω cm) and high transmission (87%) were observed for films deposited at 400°C with an oxygen flow rate of 1.81 min^-1. The effects of the deposition temperature, oxygen flow rate and deposition time on the thickness, deposition rate, resistivity and absorption coefficient are discussed in detail.