Bipolar Conduction in SnO Thin Films

Hosono, Hideo; Ogo, Yoichi; Yanagi, Hiroshi; Kamiya, Toshio

doi:10.1149/1.3505288

Cited by 158 publications

(156 citation statements)

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“…Previous experiment has suggested that the SnO VBM is 5.8 eV below the vacuum level, 54 similar to other p-type materials, such as Cu 2 O ($5.6 eV) and Li-doped NiO ($5.5 eV). 78,79 More recent experiments, however, have revised this to being VBM 4.9 eV below the vacuum level. 80 The direct optical band gap is found to be $2.7 eV, giving moderate transparency; however, SnO also has an indirect fundamental band gap of 0.7 eV.…”

Section: -58mentioning

confidence: 99%

Understanding the defect chemistry of tin monoxide

et al. 2013

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Tin monoxide has garnered a great deal attention in the recent literature, primarily as a transparent p-type conductor. However, due to its layered structure (dictated by non-bonding dispersion forces) simulation via density functional theory often fails to accurately model the unit cell. This study applies a PBE0-vdW methodology to accurately predict both the atomic and electronic structure of SnO. Empirical van der Waals corrections improve the structure, with the calculated c/a ratio matching experiment, while the PBE0 hybrid-DFT method gives accurate band gaps (0.67 and 2.76 eV for the indirect and direct band gaps) and density of states which are in agreement with experimental spectra. This methodology has been applied to the simulation of the native intrinsic defects of SnO, to further understand the conductivity. The results indicate that n-type conductivity will not arise from intrinsic defects and that donor doping would be necessary. For p-type conduction, the Sn vacancy is seen to be the source, with the 0/À1 transition level found 0.39 eV above the valence band maximum. By considering the formation energies and transition levels of the defects at different chemical potentials, it is found that the p-type conductivity is sensitive to the O chemical potential. When the chemical potential is close to its lowest value (À2.65 eV here), the oxygen vacancy is stabilized which, whilst not leading to n-type conduction, could reduce p-type conduction by limiting the formation of hole states.

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Section: -58mentioning

confidence: 99%

Understanding the defect chemistry of tin monoxide

et al. 2013

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“…4,5 It is known that the valence band maximum (VBM) of most oxide semiconductors is mainly composed of fully occupied 2p orbitals of oxygen ions with a large electronegativity. 5,6 Hence the dispersion of the VBM band is in general small (i.e., the hole effective mass is large) and the ionization potential is large (i.e., the holes are energetically unstable), causing difficulty in p-type doping for oxide semiconductors.Fortunately, effective p-type doping and relatively high hole mobility is attained in SnO due to the hole contribution through the VBM composed of 5s 2 orbitals of Sn 2+ . 5,7 However, SnO TFTs generally operate in the depletion mode and have a high off-state current owing to the high hole concentration and the low resistivity of the SnO films.…”

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“…5,7 However, SnO TFTs generally operate in the depletion mode and have a high off-state current owing to the high hole concentration and the low resistivity of the SnO films. 7−11 It is reported that the conductivity in SnO is related to tin vacancy and controllable also by impurity doping.…”

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Effects of Pb Doping on Hole Transport Properties and Thin-Film Transistor Characteristics of SnO Thin Films

Liao

Xiao

Ran

et al. 2015

ECS J. Solid State Sci. Technol.

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Effects of Pb doping on the microstructural, optical, and hole transport properties of Sn 1−xf Pb xf O films fabricated by pulsed laser deposition were investigated. It was found that Pb was not solved in bulk ceramic samples, while solved up to x f = 0.035 in the thin films. The Pb doping enlarged the optical bandgap, decreased the hole concentration, and reduced the Hall mobility (μ Hall , from 1.95 to 0.68 cm 2 V −1 s −1 up to x f = 0.035) as x f increased. The field-effect mobility in thin-film transistors also decreased with x f (μ lin , from 0.34 to 0.0024 cm 2 V −1 s −1 ), but the deterioration of μ lin was significantly larger than that of μ Hall . It is speculated that the deterioration of μ Hall would be due to the increase in grain boundary potential barriers. Oxide semiconductors have attracted considerable attention as next-generation channel materials to replace amorphous silicon and polycrystalline silicon for thin-film transistors (TFTs), because of their high electron mobilities >10 cm 2 V −1 s −1 and excellent electrical properties due to the large bandgaps.1−3 However, the reported oxide-based TFTs with excellent performance show n-type characteristics only. The lack of high-performance p-type oxide-based TFTs impedes the realization of transparent low-power-consumption complementary circuits in various TFT applications. 4,5 It is known that the valence band maximum (VBM) of most oxide semiconductors is mainly composed of fully occupied 2p orbitals of oxygen ions with a large electronegativity. 5,6 Hence the dispersion of the VBM band is in general small (i.e., the hole effective mass is large) and the ionization potential is large (i.e., the holes are energetically unstable), causing difficulty in p-type doping for oxide semiconductors.Fortunately, effective p-type doping and relatively high hole mobility is attained in SnO due to the hole contribution through the VBM composed of 5s 2 orbitals of Sn 2+ . 5,7 However, SnO TFTs generally operate in the depletion mode and have a high off-state current owing to the high hole concentration and the low resistivity of the SnO films.7−11 It is reported that the conductivity in SnO is related to tin vacancy and controllable also by impurity doping.5,12−14 However, the previous reports on doping effects are not consistent with each other. Guo et al. reported that doping in SnO with large size dopants such as Sb or Y enhances their hole mobilities and hole concentrations, 13 the latter of which is opposite to usual concept of aliovalent ion doping (i.e., substitutions of the Sn 2+ sites by Sb 3+ /Y 3+ ions are expected to be n-type doping). In contrast, Hosono et al. gave a clear evidence that Sb 3+ doping decreases the hole mobility and the hole concentration in SnO and finally converts the carrier polarity to n-type. 5Liang et al. demonstrated that doping of SnO with Y decreases the field-effect mobility but suppresses the off-state current in SnO TFTs, even though the mechanism for the reduction in the off-state current is not clarified.14 Like SnO, ...

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“…Good p-type transparent oxide semiconductors would allow the fabrication of transparent p-n junctions, enabling new applications of invisible circuits. [4][5][6] However, nowadays, the materials still suffer from a low conductivity as compared to their n-type counterparts. 7,8 Therefore, it is crucial to find ways to improve the hole transport.…”

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Enhancement of p-type mobility in tin monoxide by native defects

Granato

Caraveo-Frescas

Alshareef

et al. 2013

Applied Physics Letters

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Transparent p-type materials with good mobility are needed to build completely transparent p-n junctions. Tin monoxide (SnO) is a promising candidate. A recent study indicates great enhancement of the hole mobility of SnO grown in Sn-rich environment [E. Fortunato et al., Appl. Phys. Lett. 97, 052105 (2010)]. Because such an environment makes the formation of defects very likely, we study defect effects on the electronic structure to explain the increased mobility. We find that Sn interstitials and O vacancies modify the valence band, inducing higher contributions of the delocalized Sn 5p orbitals as compared to the localized O 2p orbitals, thus increasing the mobility. This mechanism of valence band modification paves the way to a systematic improvement of transparent p-type semiconductors.

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Bipolar Conduction in SnO Thin Films

Cited by 158 publications

References 22 publications

Understanding the defect chemistry of tin monoxide

Understanding the defect chemistry of tin monoxide

Effects of Pb Doping on Hole Transport Properties and Thin-Film Transistor Characteristics of SnO Thin Films

Enhancement of p-type mobility in tin monoxide by native defects

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