• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.619-619
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• 2013

The interfacial state between $Ta_2O_5$ and a Si substrate during the growth of $Ta_2O_5$ films by atomic layer deposition (ALD) was investigated using in-situ synchrotron radiation photoemission spectroscopy (SRPES). A newly synthesized liquid precursor Ta($N^tBu$) $(dmamp)_2Me$ was used as the metal precursor, with Ar as a purging gas and $H_2O$ as the oxidant source. After each half reaction cycle, samples were analyzed using in-situ SRPES under ultrahigh vacuum at room temperature. SRPES analysis revealed that Ta suboxide and Si dioxide were formed at the initial stages of $Ta_2O_5$ growth. However, the Ta suboxide states almostdisappeared as the ALD cycles progressed. Consequently, the $Ta^{5+}$ state, which corresponds with the stoichiometric $Ta_2O_5$, only appeared after 4.0 cycles. Additionally, tantalum silicate was not detected at the interfacial states between $Ta_2O_5$ and Si. The measured valence band offset between $Ta_2O_5$ and the Si substrate was 3.22 eV after 3.0 cycles.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.283.2-283.2
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• 2013

The variation of chemical and interfacial state during the growth of Ta2O5 films on the Si substrate by atomic layer deposition (ALD) was investigated using in-situ synchrotron radiation photoemission spectroscopy. A newly synthesized liquid precursor Ta(NtBu)(dmamp)2Me was used as the metal precursor, with Ar as a purging gas and H2O as the oxidant source. The core-level spectra of Si 2p, Ta 4f, and O 1s revealed that Ta suboxide and Si dioxide were formed at the initial stages of Ta2O5 growth. However, the Ta suboxide states almost disappeared as the ALD cycles progressed. Consequently, the Ta5+ state, which corresponds with the stoichiometric Ta2O5, only appeared after 4.0 cycles. Additionally, tantalum silicate was not detected at the interfacial states between Ta2O5 and Si. The measured valence band offset value between Ta2O5 and the Si substrate was 3.08 eV after 2.5 cycles.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.362-362
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• 2014

Atomic layer deposition (ALD) can be regarded as a special variation of the chemical vapor deposition method for reducing film thickness. ALD is based on sequential self-limiting reactions from the gas phase to produce thin films and over-layers in the nanometer scale with perfect conformality and process controllability. These characteristics make ALD an important film deposition technique for nanoelectronics. Tantalum pentoxide ($Ta_2O_5$) has a number of applications in optics and electronics due to its superior properties, such as thermal and chemical stability, high refractive index (>2.0), low absorption in near-UV to IR regions, and high-k. In particular, the dielectric constant of amorphous $Ta_2O_5$ is typically close to 25. Accordingly, $Ta_2O_5$ has been extensively studied in various electronics such as metal oxide semiconductor field-effect transistors (FET), organic FET, dynamic random access memories (RAM), resistance RAM, etc. In this experiment, the variations of chemical and interfacial state during the growth of $Ta_2O_5$ films on the Si substrate by ALD was investigated using in-situ synchrotron radiation photoemission spectroscopy. A newly synthesized liquid precursor $Ta(N^tBu)(dmamp)_2$ Me was used as the metal precursor, with Ar as a purging gas and $H_2O$ as the oxidant source. The core-level spectra of Si 2p, Ta 4f, and O 1s revealed that Ta suboxide and Si dioxide were formed at the initial stages of $Ta_2O_5$ growth. However, the Ta suboxide states almost disappeared as the ALD cycles progressed. Consequently, the $Ta^{5+}$ state, which corresponds with the stoichiometric $Ta_2O_5$, only appeared after 4.0 cycles. Additionally, tantalum silicide was not detected at the interfacial states between $Ta_2O_5$ and Si. The measured valence band offset value between $Ta_2O_5$ and the Si substrate was 3.08 eV after 2.5 cycles.

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.140-140
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• 2007

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.8-10
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• 2010

We report the enhancement of hole injection using thermally evaporated $CuO_x$ layer between Ag anode and 4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl ($\alpha$-NPD) in top-emitting organic light-emitting diode (TEOLED). The operation voltage at the current density of $1mA/cm^2$ of TEOLEDs decreased from 6.2 V to 5.0 V as the $CuO_x$ layer inserted between Ag and $\alpha$-NPD. $\alpha$-NPD was deposited in situ on Ag/$CuO_x$ and Ag anodes, and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. The dipole energy of Ag/$CuO_x$ was lower by 0.05 eV even though Ag/$CuO_x$ had a higher work function. The work function of Ag/$CuO_x$ is higher by 0.53 eV than that of Ag, resulting in a decrease of the turn-on voltage via reduction of hole injection barrier.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.14-15
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• 2010

Recently there has been growing interest in topological insulators or the quantum spin Hall (QSH) phase, which are insulating materials with bulk band gaps but have metallic edge states that are formed topologically and robust against any non-magnetic impurity [1]. In a three-dimensional material, the two-dimensional surface states correspond to the edge states (topological metal) and their intriguing nature in terms of electronic and spin structures have been experimentally observed in bulk Bi1-xSbx single crystals [2,3,4]. However, if we want to know the transport properties of these topological metals, high purity samples as well as very low temperature will be needed because of the contribution from bulk states or impurity effects. In a recent report, it was also shown that an intriguing coupling between the surface and bulk states will occur [5]. A simple solution to this bothersome problem is to prepare a topological metal on an ultrathin film, in which the surface-to-bulk ratio is drastically increased. Therefore in the present study, we have investigated if there is a method to make an ultrathin Bi1-xSbx film on a semiconductor substrate. From reflection high-energy electron diffraction observation, it was found that single crystal Bi1-xSbx films (0${\sim}30\;{\AA}A$ can be prepared on Si(111)-$7{\times}7$. The transport properties of such films were characterized by in situ monolithic micro four-point probes [6]. The temperature dependence of the resistivity for the x=0.1 samples was insulating when the film thickness was $240\;{\AA}A$. However, it became metallic as the thickness was reduced down to $30\;{\AA}A$, indicating surface-state dominant electrical conduction. Figure 1 shows the Fermi surface of $40\;{\AA}A$ thick Bi0.92Sb0.08 (a) and Bi0.84Sb0.16 (b) films mapped by angle-resolved photoemission spectroscopy. The basic features of the electronic structure of these surface states were shown to be the same as those found on bulk surfaces, meaning that topological metals can be prepared at the surface of an ultrathin film. The details will be given in the presentation.