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Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

Crowe, IF; Papachristodoulou, N; Halsall, MP; Hylton, NP; Hulko, O; Knights, AP; Yang, P; ... Kenyon, AJ; + view all (2013) Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation. Journal of Applied Physics , 113 (2) , Article 024304. 10.1063/1.4772947. Green open access

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Abstract

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb -centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth.

Type: Article
Title: Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.4772947
Publisher version: http://dx.doi.org/10.1063/1.4772947
Language: English
Additional information: © 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Crowe, IF, et al. (2013) Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation. Journal of Applied Physics , 113 (2) , Article 024304 and may be found at http://dx.doi.org/10.1063/1.4772947
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/1382116
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