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

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:

Seán R. Kavanagh

September 17, 2022

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  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).