Supporting Information for:
Size-Dependence of Acceptor and Donor Levels of
Boron and Phosphorus Codoped Colloidal Silicon
Nanocrystals
Yusuke Hori, Shinya Kano, Hiroshi Sugimoto, Kenji Imakita, Minoru Fujii*
Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe
University, Rokkodai, Nada, Kobe 657-8501, Japan.
*
e-mail: fujii@eedept.kobe-u.ac.jp
Figure S1 shows the energy level diagram of codoped Si-NCs and the definition of some terms
used in this paper. We assume that the HOMO level (EHOMO) is the acceptor level and the LUMO
level (ELUMO) is the donor level. We use the term “binding energy” to express the energy
difference between the acceptor level (EHOMO) and the valence band edge (EV) and between the
donor level (ELUMO) and the conduction band edge (EC).
The energy of the HOMO level measured from the vacuum level is denoted as “ionization
energy (IE)” We use photoemission yield spectroscopy (PYS) to determine the ionization energy.
In PYS, the yield of photoelectrons, Y, is measured as a function of the energy of excitation UV
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light (hν). The yield is empirically given by Y1/3 ∝ (hν-IE), and thus, by extrapolating the linear
region of the Y1/3 vs hν spectra, IE is obtained. The energy of the LUMO level (ELUMO) is
determined by adding the PL peak energy to those of EHOMO.
In this work the energy of the Fermi level (EF) is not directly measured, but determined by
measuring the energy difference between EF and EHOMO by X-ray photoelectron spectroscopy
(XPS). The onset of the XPS spectra corresponds to the first occupied state below the Fermi
level and thus the onset energy corresponds to EF-EHOMO.
0
EVac
Energy (ev vs. Vac)
-1
Ionization energy (IE)
-2
-3
-4
Binding energy
Conduction band edge, EC
Donor level, ELUMO
Fermi level, EF
-5
Acceptor level, EHOMO
Valence band edge, EV
Binding energy
Figure S1. Energy level diagram and the definition of terms used in this paper.
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Figure S2. (a) Derivative of PYS spectra. (b) Intensity of the derivative spectra at 5.4 eV.
Figure S3. Valence band XPS spectra of p type Si wafer: 10~15 Ωcm
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Figure S4. Valence band XPS spectra of codoped Si-NCs aged more than one month.
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Figure S5. Energy difference between Fermi levels and HOMO level as a function of diameter of
codoped Si-NCs aged more than one month.
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