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Audrius Alkauskas, Kaunas University of Technology, Carbon dimer defect as a source of the 4.1 eV luminescence in hexagonal boron nitride

Date and Time
Location
Elings Hall Room 1601
Audrius Alkauskas

Speaker

Audrius Alkauskas
Center for Physical Sciences and Technology (FTMC) and Department of Physics
Kaunas University of Technology

Bio

Audrius Alkauskas received MSc in physics from Vilnius University (Lithuania) in 2002, and PhD in theoretical physics from the University of Basel (Switzerland) in 2006. From 2006 to 2010 he was a post-doctoral fellow at EPFL (Lausanne, Switzerland). Subsequently from 2011 to 2014 he worked as an associate specialist at UCSB (Santa Barbara, USA). In 2014 Audrius Alkauskas started an independent position at the Center of Physical Sciences and Technology (FTMC) in Vilnius, Lithuania, becoming a Principal Research Fellow in 2016. From 2014 he is also a Professor in Physics at Kaunas University of Technology (Kaunas, Lithuania). The group of Audrius Alkauskas develops first-principles calculations of radiative and non-radiative processes in solids with a particular emphasis of quantum defects.

Abstract

Recently point defects in hexagonal boron nitride received a lot of interest because of the realization of single-photon emission. Quantum emission has been achieved in the red spectral region at about 2 eV [1], as well as in the near-UV region [2]. Spectral characteristics of the latter emitter are identical to the ubiquitous 4.1 eV luminescence line which has been known for several decades. Unfortunately, the atomic nature of the defect giving rise to this near-UV luminescence is not known, even though the involvement of carbon has been often invoked. In this talk it will be show how first principles calculations of (i) defect formation energies; (ii) optical transition energies; (iii) electron-phonon coupling strength; (iv) optical lifetimes; and (v) quantum efficiency of the transition can help identifying the nature of the defect. We show that it is the carbon dimer CB-CN that gives rise to the 4.1 eV luminescence. All the calculated parameters show excellent agreement with experiment. In addition, under a wide range of thermodynamic conditions the dimer is more stable than single substitutional defects, so dimers should form whenever carbon is present in the system. The presented techniques can be successfully applied to other quantum defects [4,5].

[1] T. T. Tran, K. Bray, M. J. Ford, M. Toth, and I. Aharonovich, Nat. Nanotechnol. 11, 37 (2016).
[2] R. Bourrellier, S. Meuret, A. Tararan, O. Stéphan, M. Kociak, L. H. Tizei, and A. Zobelli, Nano Lett. 16, 4317 (2016).
[3] M. Mackoit-Sinkevičienė, M. Maciaszek, C. G. Van de Walle, and A. Alkauskas, Appl. Phys. Lett. 115, 212101 (2019)
[4] M. Turiansky, A. Alkauskas, L. C. Bassett, and C. G. Van de Walle, Phys. Rev. Lett. 123, 127401 (2019)
[5] L. C. Bassett, A. Alkauskas, A. L. Exarhos, and K.-M. C. Fu, Nanophotonics 8, 1867 (2019)

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