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n-type conversion of SnS by isovalent ion substitution: Geometrical doping as a new doping route.

Ran FY, Xiao Z, Toda Y, Hiramatsu H, Hosono H, Kamiya T - Sci Rep (2015)

Bottom Line: In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates.Substituting Pb(2+) for Sn(2+) converted the majority carrier from hole to electron, and the free electron density ranged from 10(12) to 10(15) cm(-3) with the largest electron mobility of 7.0 cm(2)/(Vs).Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.

View Article: PubMed Central - PubMed

Affiliation: 1] Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan [2] Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.

ABSTRACT
Tin monosulfide (SnS) is a naturally p-type semiconductor with a layered crystal structure, but no reliable n-type SnS has been obtained by conventional aliovalent ion substitution. In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates. Substituting Pb(2+) for Sn(2+) converted the majority carrier from hole to electron, and the free electron density ranged from 10(12) to 10(15) cm(-3) with the largest electron mobility of 7.0 cm(2)/(Vs). The n-type conduction was confirmed further by the position of the Fermi level (EF) based on photoemission spectroscopy and electrical characteristics of pn heterojunctions. Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.

No MeSH data available.


Optical properties.(a) Typical optical absorption spectra and (b) (αhν)1/2 – hν plots (indirect-transition model) of  films with various xf (the xf values are indicated in the figure (a)). The values in (b) indicate the optical bandgaps obtained from the straight regions in the (αhν)1/2 – hν plots. (c) Variation of optical bandgaps with xf. Those calculated by DFT with LDA and GGA functionals are also shown.
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f3: Optical properties.(a) Typical optical absorption spectra and (b) (αhν)1/2 – hν plots (indirect-transition model) of films with various xf (the xf values are indicated in the figure (a)). The values in (b) indicate the optical bandgaps obtained from the straight regions in the (αhν)1/2 – hν plots. (c) Variation of optical bandgaps with xf. Those calculated by DFT with LDA and GGA functionals are also shown.

Mentions: Figure 2c shows a valence band structure of a (Sn0.5Pb0.5)S film measured by ultraviolet photoemission spectroscopy (UPS). A sharp peak at 1–2 eV and a broad peak at 2.5–4.5 eV can be observed, agreeing with the projected DOS (PDOS) calculated by DFT in Fig. 2e. The valence band consists mainly of S 3p orbitals, which slightly hybridized with Sn 5s, Sn 5p, Sn 5d, Pb 6s, Pb 6p, and Pb 6d orbitals. As seen in Fig. 2d, the observed EF of the (Sn0.5Pb0.5)S film is located at 0.82 eV above VBM. From the bandgap value of 1.15 eV (will be discussed for Fig. 3), the EC – EF value is estimated to be 0.33 eV, closer to conduction band minimum (CBM).


n-type conversion of SnS by isovalent ion substitution: Geometrical doping as a new doping route.

Ran FY, Xiao Z, Toda Y, Hiramatsu H, Hosono H, Kamiya T - Sci Rep (2015)

Optical properties.(a) Typical optical absorption spectra and (b) (αhν)1/2 – hν plots (indirect-transition model) of  films with various xf (the xf values are indicated in the figure (a)). The values in (b) indicate the optical bandgaps obtained from the straight regions in the (αhν)1/2 – hν plots. (c) Variation of optical bandgaps with xf. Those calculated by DFT with LDA and GGA functionals are also shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4446993&req=5

f3: Optical properties.(a) Typical optical absorption spectra and (b) (αhν)1/2 – hν plots (indirect-transition model) of films with various xf (the xf values are indicated in the figure (a)). The values in (b) indicate the optical bandgaps obtained from the straight regions in the (αhν)1/2 – hν plots. (c) Variation of optical bandgaps with xf. Those calculated by DFT with LDA and GGA functionals are also shown.
Mentions: Figure 2c shows a valence band structure of a (Sn0.5Pb0.5)S film measured by ultraviolet photoemission spectroscopy (UPS). A sharp peak at 1–2 eV and a broad peak at 2.5–4.5 eV can be observed, agreeing with the projected DOS (PDOS) calculated by DFT in Fig. 2e. The valence band consists mainly of S 3p orbitals, which slightly hybridized with Sn 5s, Sn 5p, Sn 5d, Pb 6s, Pb 6p, and Pb 6d orbitals. As seen in Fig. 2d, the observed EF of the (Sn0.5Pb0.5)S film is located at 0.82 eV above VBM. From the bandgap value of 1.15 eV (will be discussed for Fig. 3), the EC – EF value is estimated to be 0.33 eV, closer to conduction band minimum (CBM).

Bottom Line: In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates.Substituting Pb(2+) for Sn(2+) converted the majority carrier from hole to electron, and the free electron density ranged from 10(12) to 10(15) cm(-3) with the largest electron mobility of 7.0 cm(2)/(Vs).Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.

View Article: PubMed Central - PubMed

Affiliation: 1] Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan [2] Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.

ABSTRACT
Tin monosulfide (SnS) is a naturally p-type semiconductor with a layered crystal structure, but no reliable n-type SnS has been obtained by conventional aliovalent ion substitution. In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates. Substituting Pb(2+) for Sn(2+) converted the majority carrier from hole to electron, and the free electron density ranged from 10(12) to 10(15) cm(-3) with the largest electron mobility of 7.0 cm(2)/(Vs). The n-type conduction was confirmed further by the position of the Fermi level (EF) based on photoemission spectroscopy and electrical characteristics of pn heterojunctions. Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.

No MeSH data available.