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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.


Semilogarithmic plot of the temperature-dependent resistivity for SnO2:Sb films with varied film thickness.
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f2: Semilogarithmic plot of the temperature-dependent resistivity for SnO2:Sb films with varied film thickness.

Mentions: The in-plane electrical transport properties of the films were measured as a function of temperature ranging from 90 to 400 K. Figure 2 shows the plot of the temperature-dependent resistivity of each film. From these results, it can be seen that the resistivity of relatively thicker films (samples A and B) reduces as the temperature decreases, which suggests a metallic behavior. By contrast, semiconducting behavior (insulator ground state) was observed in the ultrathin film (sample D) with a thickness of 3.1 nm, for which the resistivity increases monotonically with the decrease of the temperature. As for the sample C, which possesses the thickness between those of samples B and D, its resistivity shows a very week dependence on the temperature. It is clear that a MIT has been induced by varying the SnO2:Sb film thickness from bulk value to nanoscale, and the critical thickness for this MIT should be around 7.9 nm.


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)

Semilogarithmic plot of the temperature-dependent resistivity for SnO2:Sb films with varied film thickness.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Semilogarithmic plot of the temperature-dependent resistivity for SnO2:Sb films with varied film thickness.
Mentions: The in-plane electrical transport properties of the films were measured as a function of temperature ranging from 90 to 400 K. Figure 2 shows the plot of the temperature-dependent resistivity of each film. From these results, it can be seen that the resistivity of relatively thicker films (samples A and B) reduces as the temperature decreases, which suggests a metallic behavior. By contrast, semiconducting behavior (insulator ground state) was observed in the ultrathin film (sample D) with a thickness of 3.1 nm, for which the resistivity increases monotonically with the decrease of the temperature. As for the sample C, which possesses the thickness between those of samples B and D, its resistivity shows a very week dependence on the temperature. It is clear that a MIT has been induced by varying the SnO2:Sb film thickness from bulk value to nanoscale, and the critical thickness for this MIT should be around 7.9 nm.

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.