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Oxygen effects on the interfacial electronic structure of titanyl phthalocyanine film:: p-type doping, band bending and Fermi level alignment
被引:44
作者:
Nishi, Toshio
[1
]
Kanai, Kaname
Ouchi, Yukio
Willis, Martin R.
Seki, Kazuhiko
机构:
[1] Nagoya Univ, Grad Sch Sci, Dept Chem, Chikusa Ku, Nagoya, Aichi 4648602, Japan
[2] Univ Nottingham, Sch Chem, Nottingham NG7 2RD, England
[3] Nagoya Univ, Res Ctr Mat Sci, Chikusa Ku, Nagoya, Aichi 4648602, Japan
[4] Nagoya Univ, Inst Adv Res, Chikusa Ku, Nagoya, Aichi 4648602, Japan
基金:
日本学术振兴会;
关键词:
ultraviolet photoelectron spectroscopy;
titanyl phthalocyanine;
organic semiconductor;
oxygen doping;
band bending;
Fermi level alignment;
D O I:
10.1016/j.chemphys.2006.02.004
中图分类号:
O64 [物理化学(理论化学)、化学物理学];
学科分类号:
070304 ;
081704 ;
摘要:
The effect of oxygen doping on titanyl phthalocyanine (TiOPc) film was investigated by ultraviolet photoelectron spectroscopy (UPS). The electronic structure of the interface formed between TiOPc films deposited on highly oriented pyrolytic graphite (HOPG) was clearly different between the films prepared in ultrahigh vacuum (UHV) and under O-2 atmosphere (1.3 x 10(-2) Pa). The film deposited in UHV showed downward band bending characteristic of n-type semiconductor, possibly due to residual impurities working as unintentional n-type dopants. On the other hand, the film deposited under O-2 atmosphere showed upward band bending characteristic of p-type semiconductor. Such trends, including the conversion from n- to p-type, are in excellent correspondence with reported field effect transistor characteristics of TiOPc, and clearly demonstrates that bulk TiOPc film was p-doped with oxygen. In order to examine the Fermi level alignment between TiOPc film and the substrate, the energy of the highest occupied molecular orbital (HOMO) of TiOPc relative to the Fermi level of the conductive substrate was determined for various substrates. The alignment between the Fermi level of conductive substrate and Fermi level of TiOPc film at fixed energy in the bandgap was not observed for the TiOPc film prepared in UHV, possibly because of insufficient charge density in the TiOPc film. This situation was drastically changed when the TiOPc film exposed to O-2, and clear alignment of the Fermi level fixed at 0.6 eV above the HOMO with the Fermi level of the conducting substrate was observed, probably by p-type doping effect of oxygen. These are the first direct and quantitative information about bulk oxygen doping from the viewpoint of the electronic structure. These results suggest that similar band bending with Fermi level alignment may be also achieved for other organic semiconductors under practical device conditions, and also call for caution at the comparison of experimental results obtained under UHV and ambient atmosphere, (c) 2006 Elsevier B.V. All rights reserved.
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页码:121 / 128
页数:8
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