Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals

• Published in: Nature nanotechnology Vol. 5; no. 12; pp. 878 - 884
• Main Authors: Yassievich, I. N, Timmerman, D, Buma, W. J, Gregorkiewicz, T, de Boer, W. D. A. M, Dohnalová, K, Zhang, H
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2010; Nature Publishing Group
• Subjects: 639/624/399/1099; 639/624/400; 639/766/483/1139; 639/925/357/354; Absorption; Chemistry and Materials Science; Electronics industry; Emissions; Materials Science; Nanocrystals; Nanotechnology; Nanotechnology and Microengineering; Optical properties; Silicon; Wavelengths
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/nnano.2010.236

Crystalline silicon is the most important semiconductor material in the electronics industry. However, silicon has poor optical properties because of its indirect bandgap, which prevents the efficient emission and absorption of light. The energy structure of silicon can be manipulated through quantum confinement effects, and the excitonic emission from silicon nanocrystals increases in intensity and shifts to shorter wavelengths (a blueshift) as the size of the nanocrystals is reduced. Here we report experimental evidence for a short-lived visible band in the photoluminescence spectrum of silicon nanocrystals that increases in intensity and shifts to longer wavelengths (a redshift) with smaller nanocrystal sizes. This higher intensity indicates an increased quantum efficiency, which for 2.5-nm-diameter nanocrystals is enhanced by three orders of magnitude compared to bulk silicon. We assign this band to the radiative recombination of non-equilibrium electron–hole pairs in a process that does not involve phonons. An ultrafast visible band in the photoluminescence spectrum of silicon nanocrystals increases in intensity and shifts to longer wavelengths as the size of the nanocrystals decreases.