EPJ PV Highlight - Contactless defects detection using modulated photoluminescence technique: model for a single Shockley-Read-Hall trap in a semiconductor thin layer

Details

Published on 02 May 2025

Contactless defects detection using modulated photoluminescence technique: model for a single Shockley-Read-Hall trap in a semiconductor thin layer

In order to develop efficient semiconductor devices and solar cells, there is a need to characterize electrically active defects in semiconductors. This is especially true for thin film solar cell absorbers which may be highly defective, either after deposition, or after ageing and degradation. Some efficient and well known electrical techniques such as Admittance Spectroscopy and Deep Level Transient Spectroscopy allow for determination of traps parameters. However, this requires to make junctions with the absorber (Schottky contact or PN junction) and depositing electrodes to perform measurements. We aim to develop a contactless method based on modulated photoluminescence (MPL), which may be used as a tool for material understanding, processes optimization, degradation tracking, or as a manufacturing control technique.

MPL has been used for decades for the determination of carrier lifetimes in silicon at low frequencies [1Hz-100kHz]. Once the technique was adapted to thin films with ns to µs range of lifetimes, it appears that some of the MPL data were difficult to analyse due to the presence of one or several unexpected local extrema (also called V-Shapes) in the MPL phase in Bode diagrams, when others plots exhibited classical monotonic shapes. In the article we reformulate our previous analytical model for a single Schockley Read Hall trap in a more general formulation, and validate this model by comparing to fully numerical simulations, i.e. performing a massive parametric study. 5832 parameter sets were calculated for p-doped and intrinsic materials in small and large signal conditions with both analytical and numerical time dependent resolution. This gave us a better understanding of the conditions under which V-shapes appear at low injection level. In doped materials, most observed V-shapes are a consequence of a dominant minority carrier trapping and reemission process, while less pronounced V-shapes can be due to capture processes by deep traps or majority carrier traps with concentrations close to or greater than that of the majority carriers. The situation is different in intrinsic materials, where the recombinant nature of the trap is the main reason for the appearance of V shapes.

"Contactless defects detection using modulated photoluminescence technique: model for a single Shockley-Read-Hall trap in a semiconductor thin layer" - Baptiste Bérenguier, Alban Asseko, Hiba Haddara, Sylvain Le Gall, Jean-Paul Kleider, and Jean-François Guillemoles EPJ Photovoltaics 16, 11 (2025). https://doi.org/10.1051/epjpv/2024045