Metastable Defect Structures and their Effect on Carrier Recombination (ETH Zürich Defects Workshop Poster 2022)

Poster presented at the 2022 ETH Zürich Defects Workshop.

Paper here: https://doi.org/10.1039/D2FD00043A

Other references:
Recombination at V_Cd in CdTe (involving metastable states): https://pubs.acs.org/doi/abs/10.1021/acsenergylett.1c00380
Defect Structure Searching: https://arxiv.org/abs/2207.09862
Matter Preview of Defect Structure Searching: https://www.sciencedirect.com/science/article/pii/S2590238521002733
ShakeNBreak: https://shakenbreak.readthedocs.io/en/latest/

For other research articles and updates, check out my website at:
https://seankavanagh.com/

Transcript

1. Seán R. Kavanagh, Aron Walsh, David O. Scanlon, Christoph Freysoldt; Faraday Discussions, 2022 Impact of metastable defect structures on carrier recombination Scan me for the paper link and a YouTube talk on this work! Metastable defect structures affect defect concentrations and carrier recombination a. Graph network of possible recombination paths b. Standard, two-step (SRH) electron-hole recombination c. Charge capture into a metastable defect, relaxation, capture back d. Thermal/Photo-excitation to metastable defect, capture, capture e. Excitation, charge capture, relaxation, charge capture e- / h+ Dq D*q Dq±1 Metastable defects can introduce several potential non-radiative recombination pathways, killing solar cell / LED / quantum computing performance. When can metastable defects impact recombination? Ø When energy relative to groundstate is less than the trap level: ∆E < ε(q/q±1) Should we expect metastable defects to be fast trap levels? Ø Based on conventional wisdom, if present, low-energy metastable states are likely to act as fast trapping / recombination centres (trap levels closer to band edges) Caption: Transition level positions; ground-state ε(q/q±1) & ground ↔ metastable defects ε(q/q∗±1) (left), also on a vertical energy level diagram (right). Capture into metastable states corresponds to transition levels closer to the band edge. Case Study: Tellurium Interstitials in CdTe (Tei ) The Result: h+ capture e– capture h+ capture e– capture h+ capture e– capture h+ capture e– capture Upper Orange Middle Blue Lower Orange e– h+ Captions: (Left) Charge capture potential energy surfaces (PESs) for all possible Tei (+/0) levels. (Right Upper) Resulting charge capture cross- sections σn/p versus temperature T. (Right Lower) Schematic of electron- hole recombination at Tellurium interstitials in CdTe. @Kavanagh_Sean_ sean.kavanagh.19@ucl.ac.uk S.R. Kavanagh, D.O. Scanlon, A. Walsh, and C. Freysoldt, Faraday Discuss. (2022). A. Alkauskas, Q. Yan, and C.G. Van de Walle, Phys. Rev. B 90, 075202 (2014). A. Alkauskas, C.E. Dreyer, J.L. Lyons, and C.G. Van de Walle, Phys. Rev. B 93, 201304 (2016). I. Mosquera-Lois and S.R. Kavanagh, Matter 4, 2602 (2021). S.R. Kavanagh, A. Walsh, and D.O. Scanlon, ACS Energy Lett. 6, 1392 (2021).