Oxygen effects on the interfacial electronic structure of titanyl phthalocyanine film: p-Type doping, band bending and Fermi level alignment

Origin of Carrier Types in Intrinsic Organic Semiconductors

“…The origin of such a native carrier type is, in most cases, empirically explained by the energy positions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) relative to the work function of the electrode metal. This answer is, however, too naïve and not quantitative, judging from the recent surface-science results [8][9][10][11][12][13][14] that point out the absence of universal rule for the energy alignment at the metal-organic semiconductor interfaces. In this study, we succeeded in changing the carrier injection barriers and observing the resultant change of carrier type in an organic FET.…”

“…[20] For the specimen on the modified electrode, in contrast, the formation of dipole layer might be suppressed by gas molecules remaining on the electrode. The gradual increase after the formation of the dipole layer can originate from the shielding of the electrode, unintentional doping, [12][13][14] or sample charging (when thicker than 40 nm), but there is no difference between the two conditions other than the dipole layer. Next, we investigated the carrier type of the AlPcCl film and the electronic state of the same film to reveal the relationship between them.…”

“…The carrier injection process is affected by the charge injection barrier at the interface and in many cases it is estimated empirically by taking account of the metal workfunction and the ionization potential of organic substances. Recent surface-science studies, [8][9][10][11][12][13][14] on the other hand, claimed that generation of a dipole layer at the interface often disturbs the alignment of electronic states. Under these circumstances it is important to know the precise band alignment for discussion of carrier type (p or n) in organic semiconductors.…”

“…The AlPcCl film annealed in air (triangles) is, however, located apart from the above line, indicating change in electronic structure owing to oxidation or doping. [14] This implies that the annealing in vacuum caused no effect, such as doping and oxidation, on the electronic structure of AlPcCl itself. Figure 3a shows UPS spectra aligned with respect to the Fermi energy (E F ).…”

“…[1][2][3][4][5][6][7] Discrimination between n-and p-type organic semiconductors in this context is considered not to come from their native properties but to relate to the carrier injection process at the semiconductor-metal electrode interfaces [1][2][3]7] if the problem of unintentional doping [12][13][14] and trapping [4,5] can be ignored. The carrier injection process is affected by the charge injection barrier at the interface and in many cases it is estimated empirically by taking account of the metal workfunction and the ionization potential of organic substances.…”