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Structural and optical properties of Be-doped ZnO nanocrystalline films by pulsed laser deposition
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Thin Solid Films 516 (2008) 4190 – 4193 www.elsevier.com/locate/tsf
Structural and optical properties of Be-doped ZnO nanocrystalline films by pulsed laser deposition Jun-Ki Chung a,⁎, Won-Jeong Kim b , Sang Su Kim b , Tae Kwon Song c , Cheol Jin Kim d a
Institute of Industrial Technology, Changwon National University, 9, Sarim-dong, Changwon city, Kyeongnam, 641-773, South Korea b Department of Physics, Changwon National University, Changwon, Kyeongnam, 641-773, South Korea c Department of Ceramic engineering, Changwon National University, Changwon, Kyeongnam, 641-773, South Korea d i-Cube Center, Gyeongsang National University, Jinju, Kyeongnam, 660-701, South Korea Received 17 May 2007; received in revised form 29 October 2007; accepted 2 November 2007 Available online 12 November 2007
Abstract The heteroepitaxial BexZn1 − xO(x = 0.4) (BZO) thin films were deposited on sapphire (c-Al2O3) substrates by pulsed laser deposition (PLD). BZO targets were synthesized using a traditional solid-reaction method. BZO films were deposited at a various substrate temperatures with a fixed P(O2) = 26 Pa, and the thickness of the films are estimated to be about 200 nm. Based on the x-ray diffraction analysis, BZO thin films deposited at Tsub. = 550–700 °C exhibit c-axis preferred growth. BZO films deposited at 600 and 650 °C exhibit sharp absorption edges around 400 nm measured at room temperature. The optical energy gap obtained from the transmittance spectra is about 3.43–3.64 eV, which demonstrates a possibility of the band gap engineering with a BeO–ZnO alloy using a PLD method with a single BZO target. It has been found that the crystallinity as well as the band gap of BZO films is strongly influenced by the deposition temperature. © 2007 Elsevier B.V. All rights reserved. Keywords: Be-doped ZnO (BZO); Beryllium; Zinc oxide; Pulsed laser deposition; X-ray diffraction; Optical properties
1. Introduction Semiconducting ZnO is a very interesting material for various applications in both microelectronic and optoelectronic devices, since ZnO exhibits interesting physical properties, such as directly wide band gap of 3.3 eV and high exciton binding energy of Eb = 60 meV at room temperature [1,2]. Its band structure and optical properties are very similar to those of GaN, which is known to be a good material for the fabrication of the optical device, such as light emitting diodes and laser diodes [3,4]. Because of the similarities between GaN and ZnO, ZnO has been studied as a possible replacement of GaN. When the ZnO synthesized with doping elements (Al, Ag, As, Ga, In and Mg), it has been known that doped ZnO is a wide and direct band gap semiconductor with high transparency in the visible wavelength region [5–14]. Doped-ZnO materials are very attractive in applications including ultraviolet laser, laser
⁎ Corresponding author. Tel.: +82 55 279 7411; fax: +82 55 267 0246. E-mail address: [email protected] (J.-K. Chung). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.11.004
diodes, transparent conductive contacts and solar cells. Several techniques, such as molecular beam epitaxy, radio frequency magnetron sputtering, chemical vapor deposition, and pulsed laser deposition (PLD) have been used to deposit highly c-axis oriented epitaxial ZnO films. Among these techniques, PLD has been recognized to be more useful in growing high quality metal oxide thin films than the others because of high energy of the ablated particles in the laser produced plume [15,16]. Wide band gap BexZn1 − xO thin films have been fabricated by the hybrid beam deposition method using a ZnO target and a Be source [17,18]. In this study, the heteroepitaxial BexZn1 − xO (x = 0.4) (BZO) thin films were deposited on (0 0 l) sapphire (cAl2O3) single crystals by a pulsed laser deposition with a BexZn1 − xO (x = 0.4) target. The crystalline and optical properties of the BZO films are discussed. 2. Experiments A BexZn1 − xO (x = 0.4) target has been synthesized by a conventional solid state reaction method. High purity ZnO (Zinc oxide, Aldrich chemical company, p.a. 99.99%) and BeO
J.-K. Chung et al. / Thin Solid Films 516 (2008) 4190–4193
Fig. 1. DTA curve of the Be0.4Zn0.6O powder mixture.
(Beryllium oxide Aldrich chemical company, p.a. 99.98%) powders were weighed in stoichiometric ratio. The mixture was mixed by ball milling in a high density polyethylene bottle using zirconia balls and ethanol. The uniaxially pressed BZO pellet has been sintered in the furnace at 1200 °C for 9 h. BZO films were fabricated by pulsed laser deposition on c-Al2O3 substrates using a KrF excimer laser (wavelength = 248 nm) with laser energy density of ∼ 2 J/cm 2 and repetition rate of 5 Hz. The distance between the target and the substrate was kept at 45 mm, and the base pressure of the deposition chamber at 6 × 10− 4 Pa. BZO films were deposited at a fixed P(O2) = 26 Pa, while substrate temperatures were varied from 500 to 700 °C. The estimated thickness of the BZO thin film was about 200 nm.
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Fig. 3. XRD θ-2θ patterns of Be0.4Zn0.6O films deposited at various substrate temperatures; (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C. The inset was c-lattice parameter of Be0.4Zn0.6O films as a function of substrate temperature.
To investigate reaction temperature, approximately 20 mg reactant mixtures were placed in a platinum crucible in a DTA (differential thermal analysis) apparatus (TA Instruments-SDT Q600) with alumina powders used as the reference standard. The X-ray diffraction system of GADDS (General Area Detector Diffraction System, Bruker) and X'Pert MPD 3040 diffractometer (Philips) with Cu Kα radiation (λ = 1.5418 Å) were used to analyze the crystalline structure. Surface morphologies and thickness of the BZO films were characterized using a Field Emission Scanning Electron Microscopy (FESEM, XL30 S, Philips) with an accelerating voltage of 15 kV. Optical properties
Fig. 2. 2-dimensional XRD analysis of Be0.4Zn0.6O films deposited on c-Al2O3. The Be0.4Zn0.6O thin films were deposited at different substrate temperatures (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C.
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J.-K. Chung et al. / Thin Solid Films 516 (2008) 4190–4193
the temperature range of 25–1500 °C in air with heating and cooling rate of 10 °C/min (Fig. 1). Two endothermic peaks (437 and 1065 °C) were observed from the DTA measurement of BZO powder, which may attributed to the decomposition of BZO. In comparison, it has been known that a pure ZnO powder exhibit clear without any endothermic peaks [8]. Based on the DTA measurement, BZO targets have been sintered at 500 °C for 2 h and 1200 °C for 9 h. 3.2. Crystalline and microstructure of BZO thins films
Fig. 4. FWHM values of θ-2θ scan plotted as a function of deposition temperature.
of the BZO films were measured in the range of 200- 800 nm using a Varian Cary 5000 spectrophotometer. 3. Results and discussion 3.1. Target fabrication To find out an optimum sintering condition of BZO target, a mixed (BeO)x(ZnO)1-x powder has been analyzed by DTA in
Fig. 2 shows 2-dimensional X-ray Diffraction (XRD) patterns of the BZO thin films deposited at 500–700 °C. No other diffraction spots except (0 0 2) of BZO were detected. It is clear that the crystallinity of (0 0 2) plane of BZO films improves with the higher deposition temperature. Fig. 3 shows θ-2θ scan of the BZO thin films deposited on c-Al2O3 substrate. For the film deposited at 500 °C, intensity of (0 0 2) peak of BZO was weak, which implies the crystallinity of the film is poor. As increasing the deposition temperature, the intensity of (0 0 2) peaks increased. Furthermore, c-axis lattice constants of the BZO thin films increase as increasing substrate temperatures (Fig. 3 inset), which are evident from shifted (0 0 2) peak positions of the BZO thin films. Fig. 4 shows that full width at half maximum (FWHM) values of the BZO (0 0 2) at different substrate temperature with
Fig. 5. SEM images of the pulsed laser deposited Be0.4Zn0.6O films grown at various deposition temperature for P(O2) = 26 Pa: (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C.
J.-K. Chung et al. / Thin Solid Films 516 (2008) 4190–4193
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evidence of the existence of Be in the BZO films. Furthermore, it is clearly demonstrated that the band gap of BZO can be changed by changing the deposition condition, which could be useful for band gap engineering as well as quantum well structure for semiconductor ZnO. 4. Conclusion
Fig. 6. Energy band gap of Be0.4Zn0.6O films as a function of deposition temperature.
fixed P(O2) = 26 Pa. The FWHM values decreased from 1.688 to 0.425° as growth temperature increased from 500 to 700 °C. The grain size can be calculated by the following Scherrer formula in BZO films, d¼
0:9k BcoshB
where d, λ, θB and B are the grain size in the film, x-ray wavelength (=1.54056 Å), Bragg diffraction angle of (0 0 2) plane, and FWHM values, respectively [19]. The particle sizes of the BZO films deposited at 500, 550, 600, 650, and 700 °C have been estimated to be 9, 16, 27, 31, and 34 nm, respectively. These results indicate that the high growth temperature can improve the crystallinity of the BZO film due to, probably, improved atomic mobility on the substrate, which could result in the increase of (0 0 2) peak intensity and decrease of FWHM value. The surface morphology of the BZO films grown at various deposition temperature with fixed P(O2) = 26 Pa were investigated (Fig. 5). SEM micrographs revealed that all deposition conditions formed multiform droplets because of high focused laser energy. As deposition temperature increases, the average diameter of the nano-dot shaped particles increased from 18 nm at 550 °C to 30 nm at 650 °C and this result was in agreement with XRD. 3.3. Optical properties The energy band gaps of BZO films were estimated from the transmittance measurement using UV-IR spectroscopy at room temperature. The deposition temperature dependent energy band gap of BZO films was shown in Fig. 6. By increasing deposition temperature from 500 to 700 °C, band gap energy of the BZO films decreases from 3.64 to 3.43 eV, which are still larger than that of ZnO (∼ 3.3 eV). The origin of the band gap changes are result of Be content changes in the BZO films due to difference in temperature dependent evaporation rates between Be and Zn. It is difficult to get a reliable chemical analysis for such a light element, like Be, in BZO. However, the measured band gap of the BZO could be considered as a good
BZO thin films were prepared on c-Al2O3 substrates at various temperatures from 500 to 700 °C using PLD. Highquality c-axis oriented BZO thin films have been grown at 550– 700 °C. The FWHM values decrease with the increasing substrate temperature. The optical energy gap obtained from the transmittance spectra is about 3.43–3.64 eV. In this study, the possibility of the band gap engineering with a BeO–ZnO compound has been clearly demonstrated using a simple deposition technique, PLD with a single BZO target. Acknowledgment This work has been partially supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2006-331C00087). References [1] A. Yamamoto, T. Kido, T. Goto, Y. Chen, T. Yao, A. Kasuya, Appl. Phys. Lett. 75 (1999) 469. [2] K. Nakahara, H. Takasu, P. Fons, A. Yamoda, K. Iwata, K. Matsubara, R. Hunger, S. Niki, Appl. Phys. Lett. 79 (2001) 4139. [3] H. Ohta, K. Nomura, H. Hiramatsu, K. Ueda, Solid-State Electron. 47 (2003) 2261. [4] A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, K. Ohtani, S.F. Chichibu, S. Fuke, Y. Segawa, H. Ohno, H. Koinuma, M. Kawasaki, Nat. Matters 4 (2005) 42. [5] M. Chen, Z.L. Pei, C. Sun, L.S. Wen, X. Wang, J. Cryst. Growth 220 (2000) 254. [6] S.-M. Park, T. Ikegami, K. Ebihara, Thin Solid Films 513 (2006) 90. [7] Y.R. Ryu, S. Zhu, D.C. Look, J.M. Wrobel, H.M. Jeong, H.W. White, J. Cryst. Growth 216 (2000) 330. [8] B.D. Ahn, H.S. Kang, J.H. Kim, G.H. Kim, H.W. Chang, S.Y. Lee, J. Appl. Phys. 100 (2006) 093701. [9] M. Yan, H.T. Zhang, E.J. Widjaja, R.P.H. Chang, J. Appl. Phys. 94 (2003) 5240. [10] V. Bhosle, A. Tiwari, J. Narayan, J. Appl. Phys. 100 (2006) 33713. [11] H. Kato, M. Sano, K. Miyamoto, T. Yao, J. Cryst. Growth 237/239 (2002) 538. [12] U. Grossner, J.S. Christensen, B.G. Svensson, A.Y. Kuznetsov, Superlattices Microstruct. 38 (2005) 364. [13] P. Bhattacharya, R.R. Das, R.S. Katiyar, Thin Solid Films 447/448 (2004) 564. [14] M. Lorenz, E.M. Kaidashev, A. Rahm, Th. Nobis, J. Lenzner, G. Wagner, D. Spemann, H. Hochmuth, M. Grundmann, Appl. Phys. Lett. 86 (2005) 143113. [15] X.W. Sun, H.S. Kwok, J. Appl. Phys. 86 (1999) 408. [16] R.D. Vispute, V. Talyansky, Z. Trajanovic, S. Choopun, M. Downes, R.P. Sharma, T. Venkatesan, Appl. Phys. Lett. 70 (1997) 2735. [17] Y.R. Ryu, T.S. Lee, J.A. Lubguban, A.B. Corman, H.W. White, J.H. Lee, M.S. Han, C.J. Youn, W.J. Kim, Appl. Phys. Lett. 88 (2006) 052103. [18] W.J. Kim, J.H. Lee, M.S. Han, I.-W. Park, Y.R. Ryu, T.S. Lee, J. Appl. Phys. 99 (2006) 096104. [19] B.D. Cullity, S.R. Stock, Elements of X-ray Diffraction, Prentice-Hall, 2001, p. 170.
Thin Solid Films 516 (2008) 4190 – 4193 www.elsevier.com/locate/tsf
Structural and optical properties of Be-doped ZnO nanocrystalline films by pulsed laser deposition Jun-Ki Chung a,⁎, Won-Jeong Kim b , Sang Su Kim b , Tae Kwon Song c , Cheol Jin Kim d a
Institute of Industrial Technology, Changwon National University, 9, Sarim-dong, Changwon city, Kyeongnam, 641-773, South Korea b Department of Physics, Changwon National University, Changwon, Kyeongnam, 641-773, South Korea c Department of Ceramic engineering, Changwon National University, Changwon, Kyeongnam, 641-773, South Korea d i-Cube Center, Gyeongsang National University, Jinju, Kyeongnam, 660-701, South Korea Received 17 May 2007; received in revised form 29 October 2007; accepted 2 November 2007 Available online 12 November 2007
Abstract The heteroepitaxial BexZn1 − xO(x = 0.4) (BZO) thin films were deposited on sapphire (c-Al2O3) substrates by pulsed laser deposition (PLD). BZO targets were synthesized using a traditional solid-reaction method. BZO films were deposited at a various substrate temperatures with a fixed P(O2) = 26 Pa, and the thickness of the films are estimated to be about 200 nm. Based on the x-ray diffraction analysis, BZO thin films deposited at Tsub. = 550–700 °C exhibit c-axis preferred growth. BZO films deposited at 600 and 650 °C exhibit sharp absorption edges around 400 nm measured at room temperature. The optical energy gap obtained from the transmittance spectra is about 3.43–3.64 eV, which demonstrates a possibility of the band gap engineering with a BeO–ZnO alloy using a PLD method with a single BZO target. It has been found that the crystallinity as well as the band gap of BZO films is strongly influenced by the deposition temperature. © 2007 Elsevier B.V. All rights reserved. Keywords: Be-doped ZnO (BZO); Beryllium; Zinc oxide; Pulsed laser deposition; X-ray diffraction; Optical properties
1. Introduction Semiconducting ZnO is a very interesting material for various applications in both microelectronic and optoelectronic devices, since ZnO exhibits interesting physical properties, such as directly wide band gap of 3.3 eV and high exciton binding energy of Eb = 60 meV at room temperature [1,2]. Its band structure and optical properties are very similar to those of GaN, which is known to be a good material for the fabrication of the optical device, such as light emitting diodes and laser diodes [3,4]. Because of the similarities between GaN and ZnO, ZnO has been studied as a possible replacement of GaN. When the ZnO synthesized with doping elements (Al, Ag, As, Ga, In and Mg), it has been known that doped ZnO is a wide and direct band gap semiconductor with high transparency in the visible wavelength region [5–14]. Doped-ZnO materials are very attractive in applications including ultraviolet laser, laser
⁎ Corresponding author. Tel.: +82 55 279 7411; fax: +82 55 267 0246. E-mail address: [email protected] (J.-K. Chung). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.11.004
diodes, transparent conductive contacts and solar cells. Several techniques, such as molecular beam epitaxy, radio frequency magnetron sputtering, chemical vapor deposition, and pulsed laser deposition (PLD) have been used to deposit highly c-axis oriented epitaxial ZnO films. Among these techniques, PLD has been recognized to be more useful in growing high quality metal oxide thin films than the others because of high energy of the ablated particles in the laser produced plume [15,16]. Wide band gap BexZn1 − xO thin films have been fabricated by the hybrid beam deposition method using a ZnO target and a Be source [17,18]. In this study, the heteroepitaxial BexZn1 − xO (x = 0.4) (BZO) thin films were deposited on (0 0 l) sapphire (cAl2O3) single crystals by a pulsed laser deposition with a BexZn1 − xO (x = 0.4) target. The crystalline and optical properties of the BZO films are discussed. 2. Experiments A BexZn1 − xO (x = 0.4) target has been synthesized by a conventional solid state reaction method. High purity ZnO (Zinc oxide, Aldrich chemical company, p.a. 99.99%) and BeO
J.-K. Chung et al. / Thin Solid Films 516 (2008) 4190–4193
Fig. 1. DTA curve of the Be0.4Zn0.6O powder mixture.
(Beryllium oxide Aldrich chemical company, p.a. 99.98%) powders were weighed in stoichiometric ratio. The mixture was mixed by ball milling in a high density polyethylene bottle using zirconia balls and ethanol. The uniaxially pressed BZO pellet has been sintered in the furnace at 1200 °C for 9 h. BZO films were fabricated by pulsed laser deposition on c-Al2O3 substrates using a KrF excimer laser (wavelength = 248 nm) with laser energy density of ∼ 2 J/cm 2 and repetition rate of 5 Hz. The distance between the target and the substrate was kept at 45 mm, and the base pressure of the deposition chamber at 6 × 10− 4 Pa. BZO films were deposited at a fixed P(O2) = 26 Pa, while substrate temperatures were varied from 500 to 700 °C. The estimated thickness of the BZO thin film was about 200 nm.
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Fig. 3. XRD θ-2θ patterns of Be0.4Zn0.6O films deposited at various substrate temperatures; (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C. The inset was c-lattice parameter of Be0.4Zn0.6O films as a function of substrate temperature.
To investigate reaction temperature, approximately 20 mg reactant mixtures were placed in a platinum crucible in a DTA (differential thermal analysis) apparatus (TA Instruments-SDT Q600) with alumina powders used as the reference standard. The X-ray diffraction system of GADDS (General Area Detector Diffraction System, Bruker) and X'Pert MPD 3040 diffractometer (Philips) with Cu Kα radiation (λ = 1.5418 Å) were used to analyze the crystalline structure. Surface morphologies and thickness of the BZO films were characterized using a Field Emission Scanning Electron Microscopy (FESEM, XL30 S, Philips) with an accelerating voltage of 15 kV. Optical properties
Fig. 2. 2-dimensional XRD analysis of Be0.4Zn0.6O films deposited on c-Al2O3. The Be0.4Zn0.6O thin films were deposited at different substrate temperatures (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C.
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J.-K. Chung et al. / Thin Solid Films 516 (2008) 4190–4193
the temperature range of 25–1500 °C in air with heating and cooling rate of 10 °C/min (Fig. 1). Two endothermic peaks (437 and 1065 °C) were observed from the DTA measurement of BZO powder, which may attributed to the decomposition of BZO. In comparison, it has been known that a pure ZnO powder exhibit clear without any endothermic peaks [8]. Based on the DTA measurement, BZO targets have been sintered at 500 °C for 2 h and 1200 °C for 9 h. 3.2. Crystalline and microstructure of BZO thins films
Fig. 4. FWHM values of θ-2θ scan plotted as a function of deposition temperature.
of the BZO films were measured in the range of 200- 800 nm using a Varian Cary 5000 spectrophotometer. 3. Results and discussion 3.1. Target fabrication To find out an optimum sintering condition of BZO target, a mixed (BeO)x(ZnO)1-x powder has been analyzed by DTA in
Fig. 2 shows 2-dimensional X-ray Diffraction (XRD) patterns of the BZO thin films deposited at 500–700 °C. No other diffraction spots except (0 0 2) of BZO were detected. It is clear that the crystallinity of (0 0 2) plane of BZO films improves with the higher deposition temperature. Fig. 3 shows θ-2θ scan of the BZO thin films deposited on c-Al2O3 substrate. For the film deposited at 500 °C, intensity of (0 0 2) peak of BZO was weak, which implies the crystallinity of the film is poor. As increasing the deposition temperature, the intensity of (0 0 2) peaks increased. Furthermore, c-axis lattice constants of the BZO thin films increase as increasing substrate temperatures (Fig. 3 inset), which are evident from shifted (0 0 2) peak positions of the BZO thin films. Fig. 4 shows that full width at half maximum (FWHM) values of the BZO (0 0 2) at different substrate temperature with
Fig. 5. SEM images of the pulsed laser deposited Be0.4Zn0.6O films grown at various deposition temperature for P(O2) = 26 Pa: (a) 500 °C, (b) 550 °C, (c) 600 °C, (d) 650 °C and (e) 700 °C.
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evidence of the existence of Be in the BZO films. Furthermore, it is clearly demonstrated that the band gap of BZO can be changed by changing the deposition condition, which could be useful for band gap engineering as well as quantum well structure for semiconductor ZnO. 4. Conclusion
Fig. 6. Energy band gap of Be0.4Zn0.6O films as a function of deposition temperature.
fixed P(O2) = 26 Pa. The FWHM values decreased from 1.688 to 0.425° as growth temperature increased from 500 to 700 °C. The grain size can be calculated by the following Scherrer formula in BZO films, d¼
0:9k BcoshB
where d, λ, θB and B are the grain size in the film, x-ray wavelength (=1.54056 Å), Bragg diffraction angle of (0 0 2) plane, and FWHM values, respectively [19]. The particle sizes of the BZO films deposited at 500, 550, 600, 650, and 700 °C have been estimated to be 9, 16, 27, 31, and 34 nm, respectively. These results indicate that the high growth temperature can improve the crystallinity of the BZO film due to, probably, improved atomic mobility on the substrate, which could result in the increase of (0 0 2) peak intensity and decrease of FWHM value. The surface morphology of the BZO films grown at various deposition temperature with fixed P(O2) = 26 Pa were investigated (Fig. 5). SEM micrographs revealed that all deposition conditions formed multiform droplets because of high focused laser energy. As deposition temperature increases, the average diameter of the nano-dot shaped particles increased from 18 nm at 550 °C to 30 nm at 650 °C and this result was in agreement with XRD. 3.3. Optical properties The energy band gaps of BZO films were estimated from the transmittance measurement using UV-IR spectroscopy at room temperature. The deposition temperature dependent energy band gap of BZO films was shown in Fig. 6. By increasing deposition temperature from 500 to 700 °C, band gap energy of the BZO films decreases from 3.64 to 3.43 eV, which are still larger than that of ZnO (∼ 3.3 eV). The origin of the band gap changes are result of Be content changes in the BZO films due to difference in temperature dependent evaporation rates between Be and Zn. It is difficult to get a reliable chemical analysis for such a light element, like Be, in BZO. However, the measured band gap of the BZO could be considered as a good
BZO thin films were prepared on c-Al2O3 substrates at various temperatures from 500 to 700 °C using PLD. Highquality c-axis oriented BZO thin films have been grown at 550– 700 °C. The FWHM values decrease with the increasing substrate temperature. The optical energy gap obtained from the transmittance spectra is about 3.43–3.64 eV. In this study, the possibility of the band gap engineering with a BeO–ZnO compound has been clearly demonstrated using a simple deposition technique, PLD with a single BZO target. Acknowledgment This work has been partially supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2006-331C00087). References [1] A. Yamamoto, T. Kido, T. Goto, Y. Chen, T. Yao, A. Kasuya, Appl. Phys. Lett. 75 (1999) 469. [2] K. Nakahara, H. Takasu, P. Fons, A. Yamoda, K. Iwata, K. Matsubara, R. Hunger, S. Niki, Appl. Phys. Lett. 79 (2001) 4139. [3] H. Ohta, K. Nomura, H. Hiramatsu, K. Ueda, Solid-State Electron. 47 (2003) 2261. [4] A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, K. Ohtani, S.F. Chichibu, S. Fuke, Y. Segawa, H. Ohno, H. Koinuma, M. Kawasaki, Nat. Matters 4 (2005) 42. [5] M. Chen, Z.L. Pei, C. Sun, L.S. Wen, X. Wang, J. Cryst. Growth 220 (2000) 254. [6] S.-M. Park, T. Ikegami, K. Ebihara, Thin Solid Films 513 (2006) 90. [7] Y.R. Ryu, S. Zhu, D.C. Look, J.M. Wrobel, H.M. Jeong, H.W. White, J. Cryst. Growth 216 (2000) 330. [8] B.D. Ahn, H.S. Kang, J.H. Kim, G.H. Kim, H.W. Chang, S.Y. Lee, J. Appl. Phys. 100 (2006) 093701. [9] M. Yan, H.T. Zhang, E.J. Widjaja, R.P.H. Chang, J. Appl. Phys. 94 (2003) 5240. [10] V. Bhosle, A. Tiwari, J. Narayan, J. Appl. Phys. 100 (2006) 33713. [11] H. Kato, M. Sano, K. Miyamoto, T. Yao, J. Cryst. Growth 237/239 (2002) 538. [12] U. Grossner, J.S. Christensen, B.G. Svensson, A.Y. Kuznetsov, Superlattices Microstruct. 38 (2005) 364. [13] P. Bhattacharya, R.R. Das, R.S. Katiyar, Thin Solid Films 447/448 (2004) 564. [14] M. Lorenz, E.M. Kaidashev, A. Rahm, Th. Nobis, J. Lenzner, G. Wagner, D. Spemann, H. Hochmuth, M. Grundmann, Appl. Phys. Lett. 86 (2005) 143113. [15] X.W. Sun, H.S. Kwok, J. Appl. Phys. 86 (1999) 408. [16] R.D. Vispute, V. Talyansky, Z. Trajanovic, S. Choopun, M. Downes, R.P. Sharma, T. Venkatesan, Appl. Phys. Lett. 70 (1997) 2735. [17] Y.R. Ryu, T.S. Lee, J.A. Lubguban, A.B. Corman, H.W. White, J.H. Lee, M.S. Han, C.J. Youn, W.J. Kim, Appl. Phys. Lett. 88 (2006) 052103. [18] W.J. Kim, J.H. Lee, M.S. Han, I.-W. Park, Y.R. Ryu, T.S. Lee, J. Appl. Phys. 99 (2006) 096104. [19] B.D. Cullity, S.R. Stock, Elements of X-ray Diffraction, Prentice-Hall, 2001, p. 170.