Thermal stability of silicon surface passivation by APCVD Al ₂O₃

authored by

Lachlan E. Black, Thomas Allen, Andres Cuevas, Keith R. McIntosh, Boris Veith, Jan Schmidt

Abstract

We investigate the thermal stability of silicon surface passivation provided by aluminium oxide (Al₂O₃) films deposited using atmospheric pressure chemical vapour deposition (APCVD) and fired in a belt furnace at a peak temperature of ~810 C. Firing stability is investigated for p- and n-type substrates as a function of Al₂O₃ film thickness both with and without a plasma-enhanced chemical vapour deposition (PECVD) SiN_x capping layer, and for boron-diffused surfaces with a ~10 nm Al₂O₃ film only. Excellent thermal stability of the passivation is demonstrated, with effective carrier lifetimes in n-type silicon wafers remaining stable or even improving after firing, and lifetimes in p-type wafers initially degrading slightly but recovering to above their initial values following ~10 min illumination by a halogen lamp at ~20 mW/cm ². Film thickness appears to be unimportant to stability, as does the presence of the capping layer. Surface recombination velocities of less than 3 cm/s for 1.35 Ω cm p-type and less than 2 cm/s for 1.2 Ω cm n-type substrates are measured after firing and illumination. The passivation of boron-diffused surfaces is also shown to improve slightly following firing, with a post-firing saturation current density of 42 fA/cm² on a diffusion with a sheet resistance of 100 Ω/□ and surface dopant concentration of ~1.3×10¹⁹ cm^-3. Capacitance-voltage (C-V) measurements show that short firing times result in an initial reduction of the interface defect density D_it and a slight increase of the negative insulator fixed charge density Q_f, while longer firing results in a substantial increase in both Q_f and D_it.

External Organisation(s)

Australian National University
PV Lighthouse
Institute for Solar Energy Research (ISFH)

Type

Article

Journal

Solar Energy Materials and Solar Cells

Volume

120

Pages

339-345

No. of pages

7

ISSN

0927-0248

Publication date

2014

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.1016/j.solmat.2013.05.048 (Access: Closed)
https://hdl.handle.net/1885/29928 (Access: Open)