Aluminium oxide thin film deposited by spray coating for p-type silicon surface passivation

Abstract

A simple yet reproducible method to deposit high quality aluminium oxide (AlOx) film by spray coating is presented. Excellent thickness and refractive index uniformity is demonstrated. The AlOx film was found to be nearly stoichiometric with an oxygen to aluminium ratio of 1.7 from X-ray photoelectron spectroscopy (XPS) measurements. An interfacial layer with thickness of about 2 nm was observed in transmission electron microscopy analysis. The interfacial layer was determined to be aluminium silicate from XPS data. Electrical characterization of the films on Czochralski (Cz) p-type silicon yielded dielectric constant of 6.5 and mean breakdown field of 4.7 MV cm−1. Interface state density of 8.7×1010 eV−1cm−2 and fixed charge density of −5.5×1012 cm−2 were obtained from the electrical characterization of metal insulator semiconductor capacitors. The excellent interface quality with low interface state density and high negative charge is suitable for passivation of p-type silicon in solar cell applications. Effective surface recombination velocity of 12 cm s−1 and 48 cm s−1 were obtained for Cz p-type silicon surface for annealing temperature of 750°C and 790°C respectively without the use of capping layer.