Lifetimes exceeding 1 ms in 1-Ω cm boron-doped Cz-silicon

authored by: D. C. Walter, B. Lim, K. Bothe, R. Falster, V. V. Voronkov, J. Schmidt
Abstract: We perform carrier lifetime investigations on oxygen-rich boron-doped Czochralski-grown silicon (Cz-Si) wafers. As a characteristic feature of oxygen-rich boron-doped silicon materials, their lifetime is generally limited by boron-oxygen-related defects, intensifying their recombination-active properties under illumination or, more generally speaking, minority-carrier injection. In this study, we examine the following characteristic lifetime values of boron-doped Cz-Si: τ₀ after annealing in darkness (i.e. complete boron-oxygen defect deactivation), τ_d after illumination at room-temperature (i.e. in the completely degraded state) and τ_0p after illumination at elevated temperature (i.e. after 'permanent recovery'). We show that the permanent recovery process can be strongly influenced by a rapid thermal annealing (RTA) step performed in a conventional belt-firing furnace in advance of the permanent recovery process. We show that all measured lifetimes, i.e. τ₀, τ_d as well as τ_0p, are strongly influenced by the RTA process. We observe a strong increase of the lifetime after permanent recovery, depending critically on the RTA process parameters. On 1-Ω cm Cz-Si material after permanent recovery we measure lifetimes of τ_0p(Δn=1.5×10¹⁵cm^-3)=210 μs without applying the RTA process and up to τ_0p(Δn=1.5×10¹⁵cm^-3)=2020 μs using optimized RTA conditions. Apart from the very high lifetimes achieved, the applied RTA process step also strongly influences the kinetics of the permanent recovery process. The recovery process is accelerated by almost two orders of magnitude, compared to a non-treated sample, which proves the industrial relevance of the process. We discuss the results within a recently proposed defect model which ascribes the observed dependence of the kinetics of the recovery process to the presence of boron nano-precipitates and their interaction with free interstitial boron atoms.
External Organisation(s): Institute for Solar Energy Research (ISFH)
Type: Article
Journal: Solar Energy Materials and Solar Cells
Volume: 131
Pages: 51-57
No. of pages: 7
ISSN: 0927-0248
Publication date: 12.2014
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.2014.06.011 (Access: Unknown)