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Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement.

Ke C, Zhu W, Zhang Z, Tok ES, Ling B, Pan J - Sci Rep (2015)

Bottom Line: A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition.With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect.Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

View Article: PubMed Central - PubMed

Affiliation: Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798.

ABSTRACT
A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

No MeSH data available.


A typical XRD pattern of SnO2:Sb film on  sapphire substrate.The inset shows the in-situ RHEED pattern of the as-deposited film.
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f1: A typical XRD pattern of SnO2:Sb film on sapphire substrate.The inset shows the in-situ RHEED pattern of the as-deposited film.

Mentions: The growth process of SnO2:Sb films on sapphire was in-situ monitored by the reflection high energy electron diffraction (RHEED). Similar RHEED patterns were obtained for all films. The inset picture in Fig. 1 gives a typical RHEED image of sample B with a thickness of 31.3 nm. The well-defined RHEED pattern indicates that the film is in single crystalline with Stranski-Krastanov growth mode, which is caused by the large lattice mismatch between the film and the substrate12. The phase structure was further investigated by HR-XRD. Figure 1 gives the 2θ-ω scan result of sample B, in which pure (101) orientation was achieved with no other detectable foreign phase or other orientated grains. This suggests that the SnO2:Sb thin film was epitaxially deposited with the out of plane epitaxial relationship of . The surface morphologies of the SnO2:Sb films were taken (see Figure S1 in Supplementary Information), from which continuous and smooth surfaces were revealed.


Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement.

Ke C, Zhu W, Zhang Z, Tok ES, Ling B, Pan J - Sci Rep (2015)

A typical XRD pattern of SnO2:Sb film on  sapphire substrate.The inset shows the in-situ RHEED pattern of the as-deposited film.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663506&req=5

f1: A typical XRD pattern of SnO2:Sb film on sapphire substrate.The inset shows the in-situ RHEED pattern of the as-deposited film.
Mentions: The growth process of SnO2:Sb films on sapphire was in-situ monitored by the reflection high energy electron diffraction (RHEED). Similar RHEED patterns were obtained for all films. The inset picture in Fig. 1 gives a typical RHEED image of sample B with a thickness of 31.3 nm. The well-defined RHEED pattern indicates that the film is in single crystalline with Stranski-Krastanov growth mode, which is caused by the large lattice mismatch between the film and the substrate12. The phase structure was further investigated by HR-XRD. Figure 1 gives the 2θ-ω scan result of sample B, in which pure (101) orientation was achieved with no other detectable foreign phase or other orientated grains. This suggests that the SnO2:Sb thin film was epitaxially deposited with the out of plane epitaxial relationship of . The surface morphologies of the SnO2:Sb films were taken (see Figure S1 in Supplementary Information), from which continuous and smooth surfaces were revealed.

Bottom Line: A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition.With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect.Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

View Article: PubMed Central - PubMed

Affiliation: Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798.

ABSTRACT
A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

No MeSH data available.