Thermally Activated Emission from Direct Bandgap-Like Silicon Quantum Dots

Abstract

Thermally activated emission from direct bandgap-like silicon quantum dotsNewell, K.; Saeed, S.; Poddubny, A. N.; Prokofiev, A.A.; Gregorkiewicz, T. Published in: ECS J.Solid State Science Technology DOI:10.1149/2.004306jss Link to publicationCitation for published version (APA): Dohnalova, K., Saeed, S., Poddubny, A. N., Prokofiev, A. A., & Gregorkiewicz, T. (2013). Thermally activated emission from direct bandgap-like silicon quantum dots. ECS J.Solid State Science Technology, 2(6), R97-R99. DOI: 10.1149/2.004306jss General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. A. F. Ioffe Physical-Technical Institute RAS, 19402 Saint-Petersburg, Russia Due to the covalent character of silicon-carbon (Si-C) bond, C-linked molecules on the silicon quantum dot (SiQD) surface lead to dramatic changes in wavefunctions of the excited electron-hole pairs. Some of the optical transitions are strongly modified and attain direct bandgap-like character, giving rise to bright phonon-less fast decaying emission, while many other transitions keep their typical indirect bandgap character. It appears that in C-terminated SiQDs, with diameter larger than ∼2 nm, the most efficient recombination occurs from states slightly above the ground state. This leads to thermal activation of the fast emission, dominating the photoluminescence from these SiQDs. On the other hand, in the smallest SiQDs of less than 2 nm, the lowest excited states have the direct bandgap-like character and therefore their emission becomes gradually dominant at lower temperatures, as indeed supported by our experimental observations. Indirect band gap limits optical applications of bulk silicon and silicon nanostructures. Low radiative rate compared to fast nonradiative recombination rate leads to a very low internal quantum efficiency of emission. Therefore in silicon, emission efficiency is much more sensitive to the presence of nonradiative channels than for direct bandgap materials. In order to improve the optical faculty of Si many approaches have been explored, with the most prominent ones being optical doping, 1,2 nanostructuring 3 and a combination of the two. 4 In particular, SiQDs turn out to offer many opportunities, either in form of oxygen passivated SiQDs 5 or with customizable organic passivation, 6-17 ac...

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