- Email: [email protected]
High-resolution X-ray photoelectron spectroscopy study of InTe thin film in structural phase transition from amorphous to crystalline phase
Thin Solid Films 518 (2010) 4442–4445
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
High-resolution X-ray photoelectron spectroscopy study of InTe thin film in structural phase transition from amorphous to crystalline phase Young Mi Lee a, Yongsup Park b, Chang-Woo Sun c, Jeong Yong Lee c, Hyun Joon Shin d, Yong Tae Kim e,⁎, Min-Cherl Jung a,⁎ a
Priority Research Centers Program, University of Ulsan, Ulsan 680-749, Republic of Korea Department of Physics, Kyung Hee University, 1 Hoegi-Dong, Seoul 130-701, Republic of Korea Department of Material Science and Engineering, KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea d Beamline Division, Pohang Accelerator Laboratory, Pohang 790-784, Republic of Korea e Semiconductor Materials and Devices Lab., Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-650, Republic of Korea b c
a r t i c l e
i n f o
Article history: Received 28 July 2009 Received in revised form 21 January 2010 Accepted 4 February 2010 Available online 11 February 2010 Keywords: Indium telluride Chemical state Structural phase transition X-ray photoelectron spectroscopy
a b s t r a c t We investigated the chemical states of InTe thin film in the structural phase transition from the amorphous to the crystalline phase, using high-resolution X-ray photoelectron spectroscopy with synchrotron radiation. We confirmed the structural phase transition by transmission electron microscopy. Clean amorphous InTe (a-InTe) free of oxygen impurity was obtained after Ne+ ion sputtering at the ion beam energy of 1 kV for 1 h. Additionally, we obtained crystalline InTe (c-InTe) from clean a-InTe by annealing at 250 °C in an ultra-high vacuum. During the transition to the crystalline phase, the binding energy of the Te 4d core-level was unchanged, but the peak width was somewhat wider than in the amorphous phase. In the case of the In 4d core-level, the chemical shift was 0.1 eV at the higher binding energy between the amorphous and crystalline phases. The valence band maximum was shifted at the higher binding energy of 0.34 eV. We assumed that the Te atom was almost fixed and that the In atoms moved in the tight binding energy state to the center of the 4-Te atoms. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Chalcogenide-based phase-change materials have been attracting much attention for their reversible electrical-properties' changeability between the amorphous and crystalline phases, which makes them promising potential materials for non-volatile memories such as phase-change random access memory (PRAM) [1,2]. In recent years, Ge–Sb–Te-based phase-change materials such as Ge2Sb2Te5 and Ge1Sb2Te4 have been found to have possible non-volatile memory device applications [1–3]. Also, prototype 256 and 512 Mb PRAM devices have been reported [4,5]. However, Ge–Sb–Te-based PRAM devices are prone to process errors because of their impurities (mainly oxygen) and low phase-change temperature (b180 °C), that they cannot be operated by SET and RESET [6]. To overcome these obstacles, a non-Ge–Sb–Te-based phase-change material that has a high phase-change temperature (N200 °C) and that is also impuritiesfree, is necessary. Indium telluride (InTe) material, with its photoelectric properties and structural phase transition under variable pressure and temperature, has been the subject of several recent studies [7–10]. In one
⁎ Corresponding authors. Fax: +82 52 259 1693. E-mail address: [email protected] (M.-C. Jung). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.02.013
such study, it showed a phase-change temperature of over 250 °C and a possibility for PRAM-device applications [8]. However, its chemical state and electronic structure had not yet been quantitatively investigated. In the present study, we subjected amorphous and crystalline InTe to high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation. Oxygen-free clean and amorphous InTe was obtained by Ne+ sputtering, and crystallization was transformed by the resistivity heating at 250 °C under ultra-high vacuum (UHV). 2. Experiments Amorphous InTe (a-InTe) thin film was deposited by radio-frequency magnetron sputtering onto an SiO2 (200 nm)/Si (100) wafer at room temperature. We used an InTe single target of 1:1 stoichiometry and Ar gas. The base and working pressures were 1.2 × 10− 6 and 1.5× 10− 3 torr, respectively. The deposition rate was 80 nm/min. The thickness of the deposited InTe thin film was 100 nm. To remove the surface-oxide-layer formation caused by exposure to the air, the a-InTe thin film was subjected to 1 h Ne+ (99.999%) ion sputtering at the ion beam energy of 0.6 kV, under the pressure of 1.0 × 10− 5 torr [11]. In order to effect crystallization, the oxygen-free a-InTe was annealed by resistivity heating for 5 min at the temperature of 250 °C, under the pressure of 5.0 × 10− 10 torr. The structural phase transition was confirmed by
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445
4443
transmission electron microscopy (TEM). Cross sectional TEM specimens were prepared by mechanical polishing followed by an ion milling with Ar ions. Ion milling was conducted using the liquid nitrogen cooling stage of a Fischione 1010 ion miller with the condition of 4 kV and 4 mA to suppress the unwanted crystallization by sample heating during the conventional Ar ion milling without cooling stage. Selected area electron diffraction (SAED) patterns and high-resolution TEM images were obtained with a Gatan Ultrascan 4000SP CCD camera attached to a JEOL JEM-3010 operated at 300 kV. Additionally, the chemical states of the obtained a-InTe and crystalline InTe (c-InTe) were investigated by HRXPS using the Pohang Light Source (PLS) synchrotron at beamline 8A1 (U7) [12]. The incident photon energies were 635 and 250 eV. A PHI 3057 with an Omega lens and a 16-channel detector (Physical Electronic Co.) was used as the electron analyzer. The energy resolution according to the HRXPS was better than 200 meV. The core-level spectra of the Te 4d and In 4d also were obtained. The binding energies were calibrated with reference to the Au 4f7/2 level (84.0 eV) and the valence band maximum of both amorphous and crystalline InTe because the conductivity changes during the phase transition [13]. 3. Results and discussion The evidence of the structural phase transition is illustrated in Fig. 1. We confirmed the amorphous and crystalline phases of the InTe thin film by TEM. The c-InTe thin film was formed by in-situ annealing the oxygen-free a-InTe at 250 °C under UHV. To obtain the clean oxygen-free a-InTe surface, we performed Ne+ ion sputtering for 1 h at the beam energy of 1 kV under the working pressure of 1.0 × 10− 5 torr. We measured the chemical states of the oxygen-free a-InTe by HRXPS at the beam energy of 635 eV (Fig. 2). The Te 4d5/2 core-level appeared in two peaks with the binding energies of 43.7 and 40.0 eV, respectively. We assumed that the one peak at 43.7 eV had the chemical state of oxide and that the other peak, at 40.0 eV, had that of a-InTe. After the sputtering, the oxide peak had disappeared, and the peak with the chemical state of a-InTe was clearly evident. Also, the In 4d core-level manifested significant spin–orbit splitting, with the energy of 0.8 eV (Fig. 2(b)) [13]. The binding energy and full-width at half maximum (FWHM) of In 4d core-level were 17.3 and 1.8 eV in the oxygen-free a-InTe, respectively. According to the valence spectra, the oxygen-free InTe was changed from a typical oxide structure to the clean a-InTe (Fig. 2(c)). In order to initiate the structural phase transition, the clean a-InTe thin film was subjected to the heating process under UHV. In Fig. 3, the
Fig. 2. (a) Te 4d, (b) In 4d core-level and (c) valence spectra of InTe with oxide and clean sample obtained by using Ne+ ion sputtering with the beam energy of 0.6 kV for 1 h.
Fig. 1. HRTEM images of InTe thin film. (a) Amorphous and (b) crystalline phases.
spectra of both the amorphous and crystalline phases are shown with the Te 4d and In 4d core-levels and the valence. We confirmed that the binding energy of the Te 4d core-levels was not changed in the transition between the amorphous and crystalline phases. However, the FWHM was increased by 0.1 eV. Also, the binding energy of the In 4d core-level was shifted by 0.1 eV at the high binding energy. Moreover, spin–orbit splitting was enhanced sharply, indicating that the InTe thin film had structural ordering. We assumed that the In atom moved with the more tight binding energy presented in and around Te atoms [14]. In Darnell et al.'s study [10], the InTe (I) type with the tetragonal structure has a semiconductor potential. Under high pressure and temperature, the structure is changed from the InTe (I) to the InTe (II) type. The InTe (II) type, with the NaCl (B1)-type structure, has a metallic property [10]. In our experimentation, we
4444
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445
Fig. 3. (a) Te 4d, (b) In 4d core-level and (c) valence spectra of InTe thin film in the phase-change from amorphous to crystalline phase.
assumed that the sample state was changed from the amorphous to the InTe (I) type, because the InTe (II) type is made from InTe (I) at the temperature of 850 °C and under 30 kbar pressure [15]. We assumed also that the In atoms in the amorphous phase were moved to the center of the 4-Te atoms in the tetragonal structure and appeared in the structural ordering. We confirmed the electrical-property change of the InTe thin film from the valence spectra of the amorphous and crystalline phases. In Fig. 3 (c), the valence band maximum for the crystalline phase was shifted at the high binding energy of 0.34 eV in the amorphous phase. However, the shapes of the valence spectra in the amorphous and crystalline phases were similar. We assumed that, although the structural phase had changed, the valence structure did not change significantly.
maximum was shifted at the higher binding energy of 0.34 eV. We assumed that the Te atom was almost fixed and that In atom moved to the 4-Te atoms in the tetragonal structure.
4. Conclusions
References
We investigated the chemical states of InTe thin film in the structural phase transition from the amorphous to the crystalline phase, using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation. a-InTe free of oxygen impurity was obtained after Ne+ ion sputtering at the ion beam energy of 1 kV for 1 h. Additionally, we obtained c-InTe from clean a-InTe by annealing at 250 °C in an ultra-high vacuum. During the phase transition, the binding energy of the Te 4d core-level was unchanged, but the peak width was somewhat wider than in the amorphous phase. In the case of the In 4d core-level, chemical shift was 0.1 eV at the higher binding energy between the amorphous and crystalline phases. The valence band
Acknowledgement The authors would like to acknowledge the financial support from Samsung Electronics Co. Ltd. and the Korean Ministry of Knowledge Economy. Also, this work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20090574). PAL is supported by the MEST and POSCO in Republic of Korea.
[1] N. Yamada, E. Ohno, K. Nishiuchi, N. Akahira, M. Takao, J. Appl. Phys. 69 (1991) 2849. [2] A.V. Kolobov, P. Fons, A.I. Frenkel, A.L. Ankudinov, J. Tominaga, T. Uruga, Nat. Mater. 3 (2004) 703. [3] Y.M. Lee, M.-C. Jung, H.J. Shin, K. Kim, S.A. Song, Appl. Phys. Lett. 92 (2008) 211913. [4] S.J. Ahn, Y.N. Hwang, Y.J. Song, S.H. Lee, S.Y. Lee, J.H. Park, C.W. Jeong, K.C. Ryoo, J.M. Shin, J.H. Park, Y. Fai, J.H. Oh, G.H. Koh, G.T. Jeong, S.H. Joo, S.H. Choi, Y.H. Son, J.C. Shin, Y.T. Kim, H.S. Jeong, K.N. Kim, Symposium on VLSI Technology, Kyoto, Japan, 2005 p. 98. [5] J.H. Oh, J.H. Park, Y.S. Lim, H.S. Lim, Y.T. Oh, J.S. Kim, J.M. Shin, J.H. Park, Y.J. Song, K.C. Ryoo, D.W. Lim, S.S. Park, J.I. Kim, J.H. Kim, J. Yu, F. Yeung, C.W. Jeong, J.H. Kong, D.H. Kang, G.H. Koh, G.T. Jeong, H.S. Jeong, Kinam Kim, International Electron Devices Meeting, San Francisco, California, USA, 2006 p. 1. [6] S.-H. Hong, M.-C. Jung, J. Hwang, B.-J. Bae, H.J. Shin, H. Lee, Semicond. Sci. Technol. 24 (2009) 1050025. [7] R. Rousina, G.K. Shibakumar, Thin Solid Films 157 (1998) 345. [8] M.D. Banus, P.M. Robinson, J. Appl. Phys. 37 (1996) 3771.
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445 [9] N. Guettari, C. Amory, M. Morsli, J.C. Bernède, A. Khelil, Thin Solid Films 431–432 (2003) 497. [10] A.J. Darnell, W.F. Libby, Phys. Rev. B 135 (1964) A1453. [11] M.-C. Jung, H.J. Shin, K. Kim, J.S. Noh, J. Chung, Appl. Phys. Lett. 89 (2006) 043503. [12] M.K. Lee, H.J. Shin, Rev. Sci. Instrum. 72 (2001) 2065.
4445
[13] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Physical Electronics, Eden Prairie, MN, 1995 p. 93. [14] S. Hüfner, Photoelectron Spectroscopy: Principles and Applications, 2nd ed. Springer-Verlag Berlin Heidelberg, New York, 1995 p. 27–68. [15] H.E. Bömmel, Bull. Am. Phys. Soc. 8 (1963) 623.
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
High-resolution X-ray photoelectron spectroscopy study of InTe thin film in structural phase transition from amorphous to crystalline phase Young Mi Lee a, Yongsup Park b, Chang-Woo Sun c, Jeong Yong Lee c, Hyun Joon Shin d, Yong Tae Kim e,⁎, Min-Cherl Jung a,⁎ a
Priority Research Centers Program, University of Ulsan, Ulsan 680-749, Republic of Korea Department of Physics, Kyung Hee University, 1 Hoegi-Dong, Seoul 130-701, Republic of Korea Department of Material Science and Engineering, KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea d Beamline Division, Pohang Accelerator Laboratory, Pohang 790-784, Republic of Korea e Semiconductor Materials and Devices Lab., Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-650, Republic of Korea b c
a r t i c l e
i n f o
Article history: Received 28 July 2009 Received in revised form 21 January 2010 Accepted 4 February 2010 Available online 11 February 2010 Keywords: Indium telluride Chemical state Structural phase transition X-ray photoelectron spectroscopy
a b s t r a c t We investigated the chemical states of InTe thin film in the structural phase transition from the amorphous to the crystalline phase, using high-resolution X-ray photoelectron spectroscopy with synchrotron radiation. We confirmed the structural phase transition by transmission electron microscopy. Clean amorphous InTe (a-InTe) free of oxygen impurity was obtained after Ne+ ion sputtering at the ion beam energy of 1 kV for 1 h. Additionally, we obtained crystalline InTe (c-InTe) from clean a-InTe by annealing at 250 °C in an ultra-high vacuum. During the transition to the crystalline phase, the binding energy of the Te 4d core-level was unchanged, but the peak width was somewhat wider than in the amorphous phase. In the case of the In 4d core-level, the chemical shift was 0.1 eV at the higher binding energy between the amorphous and crystalline phases. The valence band maximum was shifted at the higher binding energy of 0.34 eV. We assumed that the Te atom was almost fixed and that the In atoms moved in the tight binding energy state to the center of the 4-Te atoms. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Chalcogenide-based phase-change materials have been attracting much attention for their reversible electrical-properties' changeability between the amorphous and crystalline phases, which makes them promising potential materials for non-volatile memories such as phase-change random access memory (PRAM) [1,2]. In recent years, Ge–Sb–Te-based phase-change materials such as Ge2Sb2Te5 and Ge1Sb2Te4 have been found to have possible non-volatile memory device applications [1–3]. Also, prototype 256 and 512 Mb PRAM devices have been reported [4,5]. However, Ge–Sb–Te-based PRAM devices are prone to process errors because of their impurities (mainly oxygen) and low phase-change temperature (b180 °C), that they cannot be operated by SET and RESET [6]. To overcome these obstacles, a non-Ge–Sb–Te-based phase-change material that has a high phase-change temperature (N200 °C) and that is also impuritiesfree, is necessary. Indium telluride (InTe) material, with its photoelectric properties and structural phase transition under variable pressure and temperature, has been the subject of several recent studies [7–10]. In one
⁎ Corresponding authors. Fax: +82 52 259 1693. E-mail address: [email protected] (M.-C. Jung). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.02.013
such study, it showed a phase-change temperature of over 250 °C and a possibility for PRAM-device applications [8]. However, its chemical state and electronic structure had not yet been quantitatively investigated. In the present study, we subjected amorphous and crystalline InTe to high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation. Oxygen-free clean and amorphous InTe was obtained by Ne+ sputtering, and crystallization was transformed by the resistivity heating at 250 °C under ultra-high vacuum (UHV). 2. Experiments Amorphous InTe (a-InTe) thin film was deposited by radio-frequency magnetron sputtering onto an SiO2 (200 nm)/Si (100) wafer at room temperature. We used an InTe single target of 1:1 stoichiometry and Ar gas. The base and working pressures were 1.2 × 10− 6 and 1.5× 10− 3 torr, respectively. The deposition rate was 80 nm/min. The thickness of the deposited InTe thin film was 100 nm. To remove the surface-oxide-layer formation caused by exposure to the air, the a-InTe thin film was subjected to 1 h Ne+ (99.999%) ion sputtering at the ion beam energy of 0.6 kV, under the pressure of 1.0 × 10− 5 torr [11]. In order to effect crystallization, the oxygen-free a-InTe was annealed by resistivity heating for 5 min at the temperature of 250 °C, under the pressure of 5.0 × 10− 10 torr. The structural phase transition was confirmed by
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445
4443
transmission electron microscopy (TEM). Cross sectional TEM specimens were prepared by mechanical polishing followed by an ion milling with Ar ions. Ion milling was conducted using the liquid nitrogen cooling stage of a Fischione 1010 ion miller with the condition of 4 kV and 4 mA to suppress the unwanted crystallization by sample heating during the conventional Ar ion milling without cooling stage. Selected area electron diffraction (SAED) patterns and high-resolution TEM images were obtained with a Gatan Ultrascan 4000SP CCD camera attached to a JEOL JEM-3010 operated at 300 kV. Additionally, the chemical states of the obtained a-InTe and crystalline InTe (c-InTe) were investigated by HRXPS using the Pohang Light Source (PLS) synchrotron at beamline 8A1 (U7) [12]. The incident photon energies were 635 and 250 eV. A PHI 3057 with an Omega lens and a 16-channel detector (Physical Electronic Co.) was used as the electron analyzer. The energy resolution according to the HRXPS was better than 200 meV. The core-level spectra of the Te 4d and In 4d also were obtained. The binding energies were calibrated with reference to the Au 4f7/2 level (84.0 eV) and the valence band maximum of both amorphous and crystalline InTe because the conductivity changes during the phase transition [13]. 3. Results and discussion The evidence of the structural phase transition is illustrated in Fig. 1. We confirmed the amorphous and crystalline phases of the InTe thin film by TEM. The c-InTe thin film was formed by in-situ annealing the oxygen-free a-InTe at 250 °C under UHV. To obtain the clean oxygen-free a-InTe surface, we performed Ne+ ion sputtering for 1 h at the beam energy of 1 kV under the working pressure of 1.0 × 10− 5 torr. We measured the chemical states of the oxygen-free a-InTe by HRXPS at the beam energy of 635 eV (Fig. 2). The Te 4d5/2 core-level appeared in two peaks with the binding energies of 43.7 and 40.0 eV, respectively. We assumed that the one peak at 43.7 eV had the chemical state of oxide and that the other peak, at 40.0 eV, had that of a-InTe. After the sputtering, the oxide peak had disappeared, and the peak with the chemical state of a-InTe was clearly evident. Also, the In 4d core-level manifested significant spin–orbit splitting, with the energy of 0.8 eV (Fig. 2(b)) [13]. The binding energy and full-width at half maximum (FWHM) of In 4d core-level were 17.3 and 1.8 eV in the oxygen-free a-InTe, respectively. According to the valence spectra, the oxygen-free InTe was changed from a typical oxide structure to the clean a-InTe (Fig. 2(c)). In order to initiate the structural phase transition, the clean a-InTe thin film was subjected to the heating process under UHV. In Fig. 3, the
Fig. 2. (a) Te 4d, (b) In 4d core-level and (c) valence spectra of InTe with oxide and clean sample obtained by using Ne+ ion sputtering with the beam energy of 0.6 kV for 1 h.
Fig. 1. HRTEM images of InTe thin film. (a) Amorphous and (b) crystalline phases.
spectra of both the amorphous and crystalline phases are shown with the Te 4d and In 4d core-levels and the valence. We confirmed that the binding energy of the Te 4d core-levels was not changed in the transition between the amorphous and crystalline phases. However, the FWHM was increased by 0.1 eV. Also, the binding energy of the In 4d core-level was shifted by 0.1 eV at the high binding energy. Moreover, spin–orbit splitting was enhanced sharply, indicating that the InTe thin film had structural ordering. We assumed that the In atom moved with the more tight binding energy presented in and around Te atoms [14]. In Darnell et al.'s study [10], the InTe (I) type with the tetragonal structure has a semiconductor potential. Under high pressure and temperature, the structure is changed from the InTe (I) to the InTe (II) type. The InTe (II) type, with the NaCl (B1)-type structure, has a metallic property [10]. In our experimentation, we
4444
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445
Fig. 3. (a) Te 4d, (b) In 4d core-level and (c) valence spectra of InTe thin film in the phase-change from amorphous to crystalline phase.
assumed that the sample state was changed from the amorphous to the InTe (I) type, because the InTe (II) type is made from InTe (I) at the temperature of 850 °C and under 30 kbar pressure [15]. We assumed also that the In atoms in the amorphous phase were moved to the center of the 4-Te atoms in the tetragonal structure and appeared in the structural ordering. We confirmed the electrical-property change of the InTe thin film from the valence spectra of the amorphous and crystalline phases. In Fig. 3 (c), the valence band maximum for the crystalline phase was shifted at the high binding energy of 0.34 eV in the amorphous phase. However, the shapes of the valence spectra in the amorphous and crystalline phases were similar. We assumed that, although the structural phase had changed, the valence structure did not change significantly.
maximum was shifted at the higher binding energy of 0.34 eV. We assumed that the Te atom was almost fixed and that In atom moved to the 4-Te atoms in the tetragonal structure.
4. Conclusions
References
We investigated the chemical states of InTe thin film in the structural phase transition from the amorphous to the crystalline phase, using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation. a-InTe free of oxygen impurity was obtained after Ne+ ion sputtering at the ion beam energy of 1 kV for 1 h. Additionally, we obtained c-InTe from clean a-InTe by annealing at 250 °C in an ultra-high vacuum. During the phase transition, the binding energy of the Te 4d core-level was unchanged, but the peak width was somewhat wider than in the amorphous phase. In the case of the In 4d core-level, chemical shift was 0.1 eV at the higher binding energy between the amorphous and crystalline phases. The valence band
Acknowledgement The authors would like to acknowledge the financial support from Samsung Electronics Co. Ltd. and the Korean Ministry of Knowledge Economy. Also, this work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20090574). PAL is supported by the MEST and POSCO in Republic of Korea.
[1] N. Yamada, E. Ohno, K. Nishiuchi, N. Akahira, M. Takao, J. Appl. Phys. 69 (1991) 2849. [2] A.V. Kolobov, P. Fons, A.I. Frenkel, A.L. Ankudinov, J. Tominaga, T. Uruga, Nat. Mater. 3 (2004) 703. [3] Y.M. Lee, M.-C. Jung, H.J. Shin, K. Kim, S.A. Song, Appl. Phys. Lett. 92 (2008) 211913. [4] S.J. Ahn, Y.N. Hwang, Y.J. Song, S.H. Lee, S.Y. Lee, J.H. Park, C.W. Jeong, K.C. Ryoo, J.M. Shin, J.H. Park, Y. Fai, J.H. Oh, G.H. Koh, G.T. Jeong, S.H. Joo, S.H. Choi, Y.H. Son, J.C. Shin, Y.T. Kim, H.S. Jeong, K.N. Kim, Symposium on VLSI Technology, Kyoto, Japan, 2005 p. 98. [5] J.H. Oh, J.H. Park, Y.S. Lim, H.S. Lim, Y.T. Oh, J.S. Kim, J.M. Shin, J.H. Park, Y.J. Song, K.C. Ryoo, D.W. Lim, S.S. Park, J.I. Kim, J.H. Kim, J. Yu, F. Yeung, C.W. Jeong, J.H. Kong, D.H. Kang, G.H. Koh, G.T. Jeong, H.S. Jeong, Kinam Kim, International Electron Devices Meeting, San Francisco, California, USA, 2006 p. 1. [6] S.-H. Hong, M.-C. Jung, J. Hwang, B.-J. Bae, H.J. Shin, H. Lee, Semicond. Sci. Technol. 24 (2009) 1050025. [7] R. Rousina, G.K. Shibakumar, Thin Solid Films 157 (1998) 345. [8] M.D. Banus, P.M. Robinson, J. Appl. Phys. 37 (1996) 3771.
Y.M. Lee et al. / Thin Solid Films 518 (2010) 4442–4445 [9] N. Guettari, C. Amory, M. Morsli, J.C. Bernède, A. Khelil, Thin Solid Films 431–432 (2003) 497. [10] A.J. Darnell, W.F. Libby, Phys. Rev. B 135 (1964) A1453. [11] M.-C. Jung, H.J. Shin, K. Kim, J.S. Noh, J. Chung, Appl. Phys. Lett. 89 (2006) 043503. [12] M.K. Lee, H.J. Shin, Rev. Sci. Instrum. 72 (2001) 2065.
4445
[13] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Physical Electronics, Eden Prairie, MN, 1995 p. 93. [14] S. Hüfner, Photoelectron Spectroscopy: Principles and Applications, 2nd ed. Springer-Verlag Berlin Heidelberg, New York, 1995 p. 27–68. [15] H.E. Bömmel, Bull. Am. Phys. Soc. 8 (1963) 623.