Impact of metastable defect structures on carrier recombination in semiconductors

Presentation given to the 3D Materials Lab group in the Colorado School of Mines, led by Prashun Gorai https://www.prashungorai.org/, focused on our recent publication Impact of metastable defect structures on carrier recombination in semiconductors (https://doi.org/10.1039/D2FD00043A)

Also discussed are our recent papers:
https://pubs.acs.org/doi/abs/10.1021/acsenergylett.1c00380
https://www.sciencedirect.com/science/article/pii/S2590238521002733

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

Transcript

1. Impact of metastable defect
   structures on carrier recombination
   in semiconductors
   Seán R. Kavanagh
   Colorado School of Mines,
   15th Apr 2022
   Profs: Aron Walsh (Imperial) & David
   Scanlon (UCL)
   sean.kavanagh.19@ucl.ac.uk
   e- / h+
   Dq
   D*q
   Dq±1
   

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2. Impact of metastable defect
   structures on carrier recombination
   in semiconductors
   Seán R. Kavanagh
   Colorado School of Mines,
   15th Apr 2022
   Profs: Aron Walsh (Imperial) & David
   Scanlon (UCL)
   sean.kavanagh.19@ucl.ac.uk
   e- / h+
   Dq
   D*q
   Dq±1
   

   View Slide

3. A Little Bit About Me
   • Undergraduate: Nanoscience, Physics &
   Chemistry of Advanced Materials at Trinity
   College Dublin, Ireland.
   • PhD: Modelling Solid-State Photovoltaic
   Materials, with an emphasis on defects and
   disorder, at Imperial College London &
   University College London.
   • 🥾🏔🏃🏋🏂🎥🍻☕🍕🍱🕺
   

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4. Defects: Flash Introduction
   4
   𝐺 = 𝐻 − 𝑇𝑆
   𝑐!
   = 𝑔exp
   −Δ𝐻
   𝑘"
   𝑇
   

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5. Motivation
   5
   

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6. Example: VCd
   0 in CdTe
   I. Mosquera-Lois and S. R. Kavanagh, Matter, 2021, 4, 2602–2605.
   

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7. Motivation
   7
   I. Mosquera-Lois and S. R. Kavanagh, Matter, 2021, 4, 2602–2605.
   

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8. Defect Dynamics
   • Alkauskas et al., Role of Excited States in
   SRH Recombination in Wide-Band-Gap
   Semiconductors, Phys. Rev. B, 2016. (LED
   Efficiency in GaN)
   • L.W. Wang, S.H. Wei et al., Non-Radiative
   Carrier Recombination Enhanced by Two-
   Level Process, Scientific Reports, 2016.
   (Solar Efficiency in CdTe; TeCd
   )
   • Guo et al., Nonradiative Carrier
   Recombination Enhanced by Vacancy
   Defects in Ionic II-VI Semiconductors,
   Phys. Rev. Applied, 2021. (Vse
   in ZnSe)
   S. R. Kavanagh, Aron Walsh and D. O. Scanlon, Rapid Recombination by Cadmium
   Vacancies in CdTe, ACS Energy Lett. 2021, 6, 4, 1392–1398
   

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9. Potential Structural Transitions
   Degenerate Minima: Thermal Excitation:
   Thermal Relaxation: Photo Excitation:
   E
   Q
   e- / h+
   e- / h+
   e- / h+
   

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10. 10
    a. Graph network of potential recombination pathways
    b. Standard electron-hole recombination
    c. Capture into metastable, relax, capture back
    d. Excite to metastable, capture, capture
    e. Excite, capture, relax, capture
    

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11. View Slide

12. Case Study: Tei
    in CdTe
    12
    

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13. 13
    Case Study: Tei
    in CdTe
    

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14. 14
    Upper
    Orange
    Middle
    Blue
    Lower
    Orange
    e–
    h+
    

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15. 15
    h+ capture
    e– capture
    h+ capture
    e– capture
    h+ capture
    e– capture
    h+ capture
    e– capture
    Upper
    Orange
    Middle
    Blue
    Lower
    Orange
    e–
    h+
    

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16. View Slide

17. CdTe: Tei
    Recombination Kinetics
    17
    

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18. Conclusions
    Defect dynamics can be crucial for
    understanding their impact on device
    performance.
    -> Demonstrated by Tei
    , where metastability
    catalyses a 4-step recombination cycle.
    Metastable defect structures potentially more
    important to non-radiative recombination than
    currently understood, particularly with:
    - Emerging ionic-covalent inorganic materials
    - Highly mobile defects
    Thanks to MPIE for the ‘Max Planck Travel
    Award’!
    Kavanagh, S. R.; Scanlon, D. O.; Walsh, A.; Freysoldt, C.
    Faraday Discuss. 2022.
    https://doi.org/10.1039/D2FD00043A.
    

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