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).
   

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