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Characterization of NiO thin film grown by two-step processes
ARTICLE IN PRESS Physica B 404 (2009) 1058–1060
Contents lists available at ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Characterization of NiO thin film grown by two-step processes Xin Wang , Ye Li, GuoZheng Wang, Rong Xiang, DeLong Jiang, ShenCheng Fu, Kui Wu, XiaoYu Yang, QingDuo DuanMu, JingQuan Tian, LiChen Fu School of Science, Changchun University of Science and Technology, Changchun, Jilin 130022, China
a r t i c l e in f o
a b s t r a c t
Article history: Received 12 January 2008 Received in revised form 28 September 2008 Accepted 30 October 2008
NiOx thin films were grown on quartz-glass substrates by two-step process: oxidation of metal Ni thin film which was obtained by vacuum evaporation method. The structural, optical and electrical properties of NiOx thin film were investigated by X-ray diffraction, absorption spectra and Hall measurement, respectively. The oxidation temperature could influence the structural, electrical and optical properties of NiOx thin film. At lower oxidation temperature (623 K), the oxidation process was not finished completely. With the increase of oxidation temperature, Ni thin films were totally oxidized into p-type NiO thin films and the optical absorption edge became steeper. Furthermore, the conductivity and carrier concentration of p-type NiO thin film decreased with the increase of oxidation temperature. & 2008 Elsevier B.V. All rights reserved.
PACS: 68.55.Ag 78.66.Li 81.15.Ef 81.65.Mq Keywords: Nickel oxide Vacuum evaporation Oxidation X-ray diffraction Absorption spectra Hall measurement
1. Introduction Recently, transparent conducting oxides (TCO) have been widely studied due to their wide applications such as transparent electrodes for liquid crystal displays, light-emitting diodes and solar cells [1,2]. However, most of TCO are n-type semiconductors (such as Sn–In2O3, Al-doped ZnO, and Sb-doped SnO2) resulting from extrinsic donors as well as intrinsic donors. For large scale opto-electronic device applications, transparent conducting p-type oxide semiconductors are mostly required, and nickel oxide (NiO) is an interesting candidate of this class with low p-type conductivity [3–5]. NiO is a semiconductor compound, having an energy gap of 3.6–4.0 eV [3]. Although, stoichiometric NiO material is an isolator [5], the resistivity of NiO thin films can be lowered by the increase of Ni vacancies and/or interstitial oxygen in NiO crystallites [5]. NiO thin film has excellent chemical stability, as well as excellent optical, electrical and magnetic properties. So it can also been used as antiferromagnetic material [6], functional layer material for chemical sensors [7], it can also be used as material for electrochromic display devices [8]. As for the fabrication methods, sol–gel [9], spray pyrolysis [10], plasma Corresponding author. Tel.: +86 43185582273.
E-mail address: [email protected] (X. Wang). 0921-4526/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2008.10.059
enhanced chemical vapor deposition [11], pulsed laser deposition [4,12–14] and magnetron sputtering [15–17] had been widely used to grow NiO thin film. Makhlouf also reported that NiO thin films can be obtained by high-temperature oxidation of nickel [18]. They found that single NiO phase thin films could be formed by hightemperature oxidation of nickel foils at 973 K. They also investigated the direct current (DC), the alternating current (AC) conductivities and dielectric properties of NiO thin film at different temperatures. However, the structural and optical properties of NiO thin films fabricated by this method were not available. In this paper, NiO thin films were grown by a two-step process: firstly, a layer of metal Ni thin film was evaporated on the quartzglass substrate by vacuum evaporation method, and then the metal Ni thin films were annealed under oxygen ambient at the temperature of 623–923 K. X-ray diffraction (XRD) diffractograms, absorption spectra, together with the Hall measurement were used to investigate the structural, optical and electrical properties of NiO thin film grown by the two-step process, respectively.
2. Experiment Metal Ni thin films were grown on the quartz-glass substrate by vacuum evaporation method, and nickel filament with a purity
ARTICLE IN PRESS X. Wang et al. / Physica B 404 (2009) 1058–1060
of 99.9% was resistively heated using a tungsten boat under a vacuum of 106 mbar. Before the evaporation process, the quartz substrates were strictly cleaned and kept at a distance of 20 cm from the evaporation source. When a proper vacuum (106 mbar) in the vacuum chamber was achieved, metal nickel was evaporated on the quartz-glass substrate at room temperature. The thickness of the nickel thin film was about 200 nm which was measured by inline film thickness monitor (Japan). Then these metal Ni thin films were annealed under oxygen ambient in the temperature ranging from 623 to 923 K for 1 h. The purity of oxygen in the annealing process was 99.99%. Before annealing, the annealing furnace was filled with oxygen for 20 min to drive out the atmosphere, and then the quartz-glass substrate which having been covered with nickel thin film was pulled into the furnace. Next, the temperature was raised up to the setting temperature (623, 723, 823 and 923 K) and kept at this temperature for 1 h. At last, the temperature was slowly decreased to the room temperature. The thickness of the NiO thin film after the oxidation process was about 330 nm. XRD diffractograms of the annealed samples were recorded by a Rigaku O/max-RA X-ray system using CuKa (l ¼ 1.5418 A˚). The absorption spectra of the annealed samples were obtained using a double beam UV-spectrophotometer and the electrical properties of samples were measured by Hall analysis in the Van Der Pauw configuration.
3. Results and discussions Fig. 1(a) shows the XRD results of the as-deposited Ni thin film. From this figure, it can be seen that there is one diffraction peak which is located at about 44.51, it proved that we have obtained cubic structural Ni film with (111)-preferred orientation. Fig. 1(b) shows the XRD results of the as-deposited Ni thin film after annealed under oxygen ambient for 1 h at 623 K. Compared with Fig. 1(a), it can be seen that besides the diffraction peak from Ni atom which is located at 44.51, three new diffraction peaks (located at 43.31, 37.31 and 31.91, respectively) appeared in Fig. 1(b). The peak located at 43.31 is the (2 0 0) diffraction peak from cubic structural NiO thin film, the peak located at 37.31 is (111) diffraction peak from cubic structural NiO thin film, and the
Fig. 1. XRD results of the as-deposited Ni thin film (a), and the thin film after annealed under oxygen ambient for 1 h at 623 K (b), 723 K (c), 823 K (d), and 923 K (e), respectively.
1059
peak located at 31.91 is not very clear. The X-ray photoelectron spectrum (XPS) of this sample was shown as Fig. 2. From the XPS result, we can see that there were two obvious peaks which are located at 852.3 and 854 eV; these two peaks come from Ni0 and Ni2+, respectively. It seems that there was a peak at the position of 856 eV; however, this peak was not as obvious as the other two peaks. If we assumed that there was a peak at this position, this peak would come from Ni3+, thus the peak at 31.91 in Fig. 1(b) was possibly the (0 0 2) diffraction peak from hexagonal structural Ni2O3. By comparing Fig. 1(b) with Fig. 1(a), it can be concluded that most of Ni atoms had been oxidized into NiOx at the oxidation temperature of 623 K; however, a few of Ni atoms still remained and was not oxidized. Fig. 1(c)–(e) shows the XRD results of the as-deposited Ni thin film after annealing under oxygen ambient for 1 h at 723, 823 and 923 K, respectively. Compared with the XRD result (Fig. 1(b)) of NiOx thin film obtained at lower oxidation temperature (623 K), the obvious changes in XRD results (Fig. 1(c)–(e)) for NiO thin film obtained at higher oxidation temperature (723, 823 and 923 K) are the disappearance of the diffraction peaks from Ni and the peak located at 31.91. It proved that metal Ni thin film was completely oxidized at the oxidation temperature higher than 723 K. At the same time, it was found that the oxidized product of Ni thin film only existed in the form of single NiO structure (without other structure such as Ni2O3, Ni15O16). As the NiO is a direct bandgap semiconductor, by plotting the relationship between (ahv)2 and hv, we can investigate some optical properties of NiO thin film, where a is the absorption coefficient and hv is the photon energy. Fig. 3(a)–(d) shows this relationship of NiO thin film after annealing under oxygen ambient for 1 h at 623 K (a), 723 K (b), 823 K (c) and 923 K (d), respectively. It is obvious that the sample which was annealed at 623 K (Fig. 2(a)) showed a much mild absorption edge; it was possibly due to the existences of unoxidized Ni atoms, which can be proved by the XRD results (Fig. 1(a)). With the increase of oxidation temperature, the absorption edge became steeper as seen in Fig. 3(b)–(d). The value of optical bandgap of NiO thin film after annealing at 623, 723, 823 and 923 K was 3.35, 3.39, 3.41 and 3.44 eV, respectively. It proved that higher oxidation temperature is beneficial for the optical property’s improvement of NiO thin film. For the sample oxidized at 923 K, the best optical properties of NiO thin film grown by our two-step process were obtained.
Fig. 2. XPS results of the Ni atom in NiOx thin film annealed under oxygen for 1 h at 623 K.
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X. Wang et al. / Physica B 404 (2009) 1058–1060
from 1 to 105 O cm with the increase of annealing temperature, changing from p-type semiconductor to oxide characteristics. It is due to that oxygen atoms will lose from NiO thin film at higher oxidation temperature. As we know that the p-type conductivity of NiO thin film was caused by the vacancy of Ni atoms and/or by the interstitial of oxygen atoms [5], the loss of oxygen atoms will cause the decrease of p-type carrier in NiO thin films, ultimately causing the experimental result that the resistivity of NiO thin film increased with the increase of oxidation temperature.
4. Conclusions
Fig. 3. The relationship between (ahv)2 and hv for Ni thin films after annealing under oxygen ambient at 623 K (a), 723 K (b), 823 K (c) and 923 K (d), respectively.
Table 1 Electrical properties of the Ni thin film after annealed under oxygen ambient for 1 h at 623, 723, 823 and 923 K. Sample
Anneal Anneal Anneal Anneal
at at at at
623 K 723 K 823 K 923 K
Type
Resistivity (O cm)
Carrier density (cm3)
Hall mobility (cm2/Vs)
n p p p
45 496 930 1012
2.0 1017 1.4 1016 4.8 1015 7.1 1014
0.7 0.9 1.4 8.7
Table 1 shows the electrical properties of metal Ni thin film after annealing under oxygen ambient for 1 h at 623, 723, 823 and 923 K. From this table, it can be seen that Ni thin film after being oxidized at 623 K showed n-type conductivity; however, the other three samples after being oxidized at higher temperature (723, 823 and 923 K ) showed p-type conductivity. As mentioned above, NiO thin film often shows p-type conductivity due to Ni vacancies and/or interstitial oxygen, the appearance of n-type conductivity for the sample annealed at low temperature (623 K) is possibly due to the existence of Ni atoms, which can be seen from the XRD results (Fig. 1). With the increase of oxidation temperature (723, 823 and 923 K), the Ni atom was completely oxidized into single NiO phase, and the conductivity of NiOx thin film changed from n- to p-type. From this table, it can also be seen that the resistivity of p-type NiO thin film increased with the increase of the oxidation temperature, these results are similar to that reported by Kohmoto’s group [19]. Kohmoto et al. found that the electric resistivity (r) of NiO thin film increases substantially
NiOx thin films were grown on quartz-glass substrates by oxidation of metal Ni film. The structural, optical and electrical properties of NiOx thin film after annealing under oxygen ambient at 623–923 K were investigated. At lower annealing temperature (623 K), the oxidation process was not complete. With the increase of annealing temperature, the Ni atoms were totally oxidized into p-type NiO thin film and the optical absorption edge of the obtained p-type NiO thin film became steeper. At the same time, the conductivity and carrier of p-type NiO decreased with the incensement of oxidation temperature.
Acknowledgment This work was supported by Technological Development Project of Jilin province in China, no. 20080170. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
J.F. Wager, Science 300 (2003) 1245. H. Hosono, Vacuum 66 (2002) 419. H. Sato, T. Minami, S. Takata, T. Yamada, Thin Solid Films 236 (1993) 27. U.S. Joshi, Y. Matsumoto, K. Itaka, M. Sumiya, H. Koinuma, Appl. Surf. Sci. 252 (2006) 2524. D. Adler, J. Feinleib, Phys. Rev. B. 2 (1970) 3112. E. Fujii, A. Tomozawa, H. Torii, R. Takayama, Japan J. Appl. Phys. 35 (Part 2) (1996) L328. I. Hotovy, V. Rehacek, P. Siciliano, S. Capone, L. Spiess, Thin Solid Films 418 (2002) 9. K. Yoshimura, T. Miki, S. Tanemura, Japan J. Appl. Phys. 34 (Part 1) (1995) 2440. Y.R. Park, K.J. Kim, J. Cryst. Growth. 258 (2003) 380. B.A. Reguig, A. Khelil, L. Cattin, M. Morsli, J.C. Berne`de, Appl. Surf. Sci. 253 (2007) 4330. W.C. Yeh, M. Matsumura, Japan J. Appl. Phys. 36 (Part 1) (1997) 6884. U.S. Joshi, R. Takahashi, Y. Matsumoto, H. Koinuma, Thin Solid Films 486 (2005) 214. Y. Kakehi, S. Nakao, K. Satoh, T. Kusaka, J. Cryst. Growth. 237–239 (2002) 591. D. Franta, B. Negulescu, L. Thomas, P.R. Dahoo, M. Guyot, I. Ohlidal, J. Mistrik, T. Yamaguchi, Appl. Surf. Sci. 244 (1–4) (2005) 426. H.L. Chen, Y.M. Lu, W.S. Hwang, Thin Solid Films 498 (1–2) (2006) 266. Y.M. Lu, W.S. Hwang, J.S. Yang, H.C. Chuang, Thin Solid Films 420–421 (2) (2002) 54. Y. Zhou, D.H. Gu, Y.Y. Geng, F.X. Gan, Mater. Sci. Eng. B. 135 (2006) 125. S.A. Makhlouf, Thin Solid Films 516 (2008) 3112. O. Kohmoto, H. Nakagawa, Y. Isagawa, A. Chayahara, J. Magn. Magn. Mater. 226–230 (2001) 1629.
Contents lists available at ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Characterization of NiO thin film grown by two-step processes Xin Wang , Ye Li, GuoZheng Wang, Rong Xiang, DeLong Jiang, ShenCheng Fu, Kui Wu, XiaoYu Yang, QingDuo DuanMu, JingQuan Tian, LiChen Fu School of Science, Changchun University of Science and Technology, Changchun, Jilin 130022, China
a r t i c l e in f o
a b s t r a c t
Article history: Received 12 January 2008 Received in revised form 28 September 2008 Accepted 30 October 2008
NiOx thin films were grown on quartz-glass substrates by two-step process: oxidation of metal Ni thin film which was obtained by vacuum evaporation method. The structural, optical and electrical properties of NiOx thin film were investigated by X-ray diffraction, absorption spectra and Hall measurement, respectively. The oxidation temperature could influence the structural, electrical and optical properties of NiOx thin film. At lower oxidation temperature (623 K), the oxidation process was not finished completely. With the increase of oxidation temperature, Ni thin films were totally oxidized into p-type NiO thin films and the optical absorption edge became steeper. Furthermore, the conductivity and carrier concentration of p-type NiO thin film decreased with the increase of oxidation temperature. & 2008 Elsevier B.V. All rights reserved.
PACS: 68.55.Ag 78.66.Li 81.15.Ef 81.65.Mq Keywords: Nickel oxide Vacuum evaporation Oxidation X-ray diffraction Absorption spectra Hall measurement
1. Introduction Recently, transparent conducting oxides (TCO) have been widely studied due to their wide applications such as transparent electrodes for liquid crystal displays, light-emitting diodes and solar cells [1,2]. However, most of TCO are n-type semiconductors (such as Sn–In2O3, Al-doped ZnO, and Sb-doped SnO2) resulting from extrinsic donors as well as intrinsic donors. For large scale opto-electronic device applications, transparent conducting p-type oxide semiconductors are mostly required, and nickel oxide (NiO) is an interesting candidate of this class with low p-type conductivity [3–5]. NiO is a semiconductor compound, having an energy gap of 3.6–4.0 eV [3]. Although, stoichiometric NiO material is an isolator [5], the resistivity of NiO thin films can be lowered by the increase of Ni vacancies and/or interstitial oxygen in NiO crystallites [5]. NiO thin film has excellent chemical stability, as well as excellent optical, electrical and magnetic properties. So it can also been used as antiferromagnetic material [6], functional layer material for chemical sensors [7], it can also be used as material for electrochromic display devices [8]. As for the fabrication methods, sol–gel [9], spray pyrolysis [10], plasma Corresponding author. Tel.: +86 43185582273.
E-mail address: [email protected] (X. Wang). 0921-4526/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2008.10.059
enhanced chemical vapor deposition [11], pulsed laser deposition [4,12–14] and magnetron sputtering [15–17] had been widely used to grow NiO thin film. Makhlouf also reported that NiO thin films can be obtained by high-temperature oxidation of nickel [18]. They found that single NiO phase thin films could be formed by hightemperature oxidation of nickel foils at 973 K. They also investigated the direct current (DC), the alternating current (AC) conductivities and dielectric properties of NiO thin film at different temperatures. However, the structural and optical properties of NiO thin films fabricated by this method were not available. In this paper, NiO thin films were grown by a two-step process: firstly, a layer of metal Ni thin film was evaporated on the quartzglass substrate by vacuum evaporation method, and then the metal Ni thin films were annealed under oxygen ambient at the temperature of 623–923 K. X-ray diffraction (XRD) diffractograms, absorption spectra, together with the Hall measurement were used to investigate the structural, optical and electrical properties of NiO thin film grown by the two-step process, respectively.
2. Experiment Metal Ni thin films were grown on the quartz-glass substrate by vacuum evaporation method, and nickel filament with a purity
ARTICLE IN PRESS X. Wang et al. / Physica B 404 (2009) 1058–1060
of 99.9% was resistively heated using a tungsten boat under a vacuum of 106 mbar. Before the evaporation process, the quartz substrates were strictly cleaned and kept at a distance of 20 cm from the evaporation source. When a proper vacuum (106 mbar) in the vacuum chamber was achieved, metal nickel was evaporated on the quartz-glass substrate at room temperature. The thickness of the nickel thin film was about 200 nm which was measured by inline film thickness monitor (Japan). Then these metal Ni thin films were annealed under oxygen ambient in the temperature ranging from 623 to 923 K for 1 h. The purity of oxygen in the annealing process was 99.99%. Before annealing, the annealing furnace was filled with oxygen for 20 min to drive out the atmosphere, and then the quartz-glass substrate which having been covered with nickel thin film was pulled into the furnace. Next, the temperature was raised up to the setting temperature (623, 723, 823 and 923 K) and kept at this temperature for 1 h. At last, the temperature was slowly decreased to the room temperature. The thickness of the NiO thin film after the oxidation process was about 330 nm. XRD diffractograms of the annealed samples were recorded by a Rigaku O/max-RA X-ray system using CuKa (l ¼ 1.5418 A˚). The absorption spectra of the annealed samples were obtained using a double beam UV-spectrophotometer and the electrical properties of samples were measured by Hall analysis in the Van Der Pauw configuration.
3. Results and discussions Fig. 1(a) shows the XRD results of the as-deposited Ni thin film. From this figure, it can be seen that there is one diffraction peak which is located at about 44.51, it proved that we have obtained cubic structural Ni film with (111)-preferred orientation. Fig. 1(b) shows the XRD results of the as-deposited Ni thin film after annealed under oxygen ambient for 1 h at 623 K. Compared with Fig. 1(a), it can be seen that besides the diffraction peak from Ni atom which is located at 44.51, three new diffraction peaks (located at 43.31, 37.31 and 31.91, respectively) appeared in Fig. 1(b). The peak located at 43.31 is the (2 0 0) diffraction peak from cubic structural NiO thin film, the peak located at 37.31 is (111) diffraction peak from cubic structural NiO thin film, and the
Fig. 1. XRD results of the as-deposited Ni thin film (a), and the thin film after annealed under oxygen ambient for 1 h at 623 K (b), 723 K (c), 823 K (d), and 923 K (e), respectively.
1059
peak located at 31.91 is not very clear. The X-ray photoelectron spectrum (XPS) of this sample was shown as Fig. 2. From the XPS result, we can see that there were two obvious peaks which are located at 852.3 and 854 eV; these two peaks come from Ni0 and Ni2+, respectively. It seems that there was a peak at the position of 856 eV; however, this peak was not as obvious as the other two peaks. If we assumed that there was a peak at this position, this peak would come from Ni3+, thus the peak at 31.91 in Fig. 1(b) was possibly the (0 0 2) diffraction peak from hexagonal structural Ni2O3. By comparing Fig. 1(b) with Fig. 1(a), it can be concluded that most of Ni atoms had been oxidized into NiOx at the oxidation temperature of 623 K; however, a few of Ni atoms still remained and was not oxidized. Fig. 1(c)–(e) shows the XRD results of the as-deposited Ni thin film after annealing under oxygen ambient for 1 h at 723, 823 and 923 K, respectively. Compared with the XRD result (Fig. 1(b)) of NiOx thin film obtained at lower oxidation temperature (623 K), the obvious changes in XRD results (Fig. 1(c)–(e)) for NiO thin film obtained at higher oxidation temperature (723, 823 and 923 K) are the disappearance of the diffraction peaks from Ni and the peak located at 31.91. It proved that metal Ni thin film was completely oxidized at the oxidation temperature higher than 723 K. At the same time, it was found that the oxidized product of Ni thin film only existed in the form of single NiO structure (without other structure such as Ni2O3, Ni15O16). As the NiO is a direct bandgap semiconductor, by plotting the relationship between (ahv)2 and hv, we can investigate some optical properties of NiO thin film, where a is the absorption coefficient and hv is the photon energy. Fig. 3(a)–(d) shows this relationship of NiO thin film after annealing under oxygen ambient for 1 h at 623 K (a), 723 K (b), 823 K (c) and 923 K (d), respectively. It is obvious that the sample which was annealed at 623 K (Fig. 2(a)) showed a much mild absorption edge; it was possibly due to the existences of unoxidized Ni atoms, which can be proved by the XRD results (Fig. 1(a)). With the increase of oxidation temperature, the absorption edge became steeper as seen in Fig. 3(b)–(d). The value of optical bandgap of NiO thin film after annealing at 623, 723, 823 and 923 K was 3.35, 3.39, 3.41 and 3.44 eV, respectively. It proved that higher oxidation temperature is beneficial for the optical property’s improvement of NiO thin film. For the sample oxidized at 923 K, the best optical properties of NiO thin film grown by our two-step process were obtained.
Fig. 2. XPS results of the Ni atom in NiOx thin film annealed under oxygen for 1 h at 623 K.
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from 1 to 105 O cm with the increase of annealing temperature, changing from p-type semiconductor to oxide characteristics. It is due to that oxygen atoms will lose from NiO thin film at higher oxidation temperature. As we know that the p-type conductivity of NiO thin film was caused by the vacancy of Ni atoms and/or by the interstitial of oxygen atoms [5], the loss of oxygen atoms will cause the decrease of p-type carrier in NiO thin films, ultimately causing the experimental result that the resistivity of NiO thin film increased with the increase of oxidation temperature.
4. Conclusions
Fig. 3. The relationship between (ahv)2 and hv for Ni thin films after annealing under oxygen ambient at 623 K (a), 723 K (b), 823 K (c) and 923 K (d), respectively.
Table 1 Electrical properties of the Ni thin film after annealed under oxygen ambient for 1 h at 623, 723, 823 and 923 K. Sample
Anneal Anneal Anneal Anneal
at at at at
623 K 723 K 823 K 923 K
Type
Resistivity (O cm)
Carrier density (cm3)
Hall mobility (cm2/Vs)
n p p p
45 496 930 1012
2.0 1017 1.4 1016 4.8 1015 7.1 1014
0.7 0.9 1.4 8.7
Table 1 shows the electrical properties of metal Ni thin film after annealing under oxygen ambient for 1 h at 623, 723, 823 and 923 K. From this table, it can be seen that Ni thin film after being oxidized at 623 K showed n-type conductivity; however, the other three samples after being oxidized at higher temperature (723, 823 and 923 K ) showed p-type conductivity. As mentioned above, NiO thin film often shows p-type conductivity due to Ni vacancies and/or interstitial oxygen, the appearance of n-type conductivity for the sample annealed at low temperature (623 K) is possibly due to the existence of Ni atoms, which can be seen from the XRD results (Fig. 1). With the increase of oxidation temperature (723, 823 and 923 K), the Ni atom was completely oxidized into single NiO phase, and the conductivity of NiOx thin film changed from n- to p-type. From this table, it can also be seen that the resistivity of p-type NiO thin film increased with the increase of the oxidation temperature, these results are similar to that reported by Kohmoto’s group [19]. Kohmoto et al. found that the electric resistivity (r) of NiO thin film increases substantially
NiOx thin films were grown on quartz-glass substrates by oxidation of metal Ni film. The structural, optical and electrical properties of NiOx thin film after annealing under oxygen ambient at 623–923 K were investigated. At lower annealing temperature (623 K), the oxidation process was not complete. With the increase of annealing temperature, the Ni atoms were totally oxidized into p-type NiO thin film and the optical absorption edge of the obtained p-type NiO thin film became steeper. At the same time, the conductivity and carrier of p-type NiO decreased with the incensement of oxidation temperature.
Acknowledgment This work was supported by Technological Development Project of Jilin province in China, no. 20080170. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
J.F. Wager, Science 300 (2003) 1245. H. Hosono, Vacuum 66 (2002) 419. H. Sato, T. Minami, S. Takata, T. Yamada, Thin Solid Films 236 (1993) 27. U.S. Joshi, Y. Matsumoto, K. Itaka, M. Sumiya, H. Koinuma, Appl. Surf. Sci. 252 (2006) 2524. D. Adler, J. Feinleib, Phys. Rev. B. 2 (1970) 3112. E. Fujii, A. Tomozawa, H. Torii, R. Takayama, Japan J. Appl. Phys. 35 (Part 2) (1996) L328. I. Hotovy, V. Rehacek, P. Siciliano, S. Capone, L. Spiess, Thin Solid Films 418 (2002) 9. K. Yoshimura, T. Miki, S. Tanemura, Japan J. Appl. Phys. 34 (Part 1) (1995) 2440. Y.R. Park, K.J. Kim, J. Cryst. Growth. 258 (2003) 380. B.A. Reguig, A. Khelil, L. Cattin, M. Morsli, J.C. Berne`de, Appl. Surf. Sci. 253 (2007) 4330. W.C. Yeh, M. Matsumura, Japan J. Appl. Phys. 36 (Part 1) (1997) 6884. U.S. Joshi, R. Takahashi, Y. Matsumoto, H. Koinuma, Thin Solid Films 486 (2005) 214. Y. Kakehi, S. Nakao, K. Satoh, T. Kusaka, J. Cryst. Growth. 237–239 (2002) 591. D. Franta, B. Negulescu, L. Thomas, P.R. Dahoo, M. Guyot, I. Ohlidal, J. Mistrik, T. Yamaguchi, Appl. Surf. Sci. 244 (1–4) (2005) 426. H.L. Chen, Y.M. Lu, W.S. Hwang, Thin Solid Films 498 (1–2) (2006) 266. Y.M. Lu, W.S. Hwang, J.S. Yang, H.C. Chuang, Thin Solid Films 420–421 (2) (2002) 54. Y. Zhou, D.H. Gu, Y.Y. Geng, F.X. Gan, Mater. Sci. Eng. B. 135 (2006) 125. S.A. Makhlouf, Thin Solid Films 516 (2008) 3112. O. Kohmoto, H. Nakagawa, Y. Isagawa, A. Chayahara, J. Magn. Magn. Mater. 226–230 (2001) 1629.