氧化鋅摻氫的成長研究中，氫氣於氧化鋅中代表的角色和造成的空缺一直是探討的方向，而最近理論預測氫氣可產生並且增強Zn1-xCoxO薄膜的室溫鐵磁性，，然實驗方面對此探討的不多，且其電傳導特性也未充分的了解。本研究自製含 5wt.% 含鈷的氧化鋅陶瓷靶材，利用射頻磁控濺鍍系統於玻璃基板上室溫成長多晶Zn0.95Co0.05O薄膜，固定成長氣壓通入不同量的氫氣於氬氣中，固定基板靶材間距 10 cm、成長功率200W，探討不同摻氫量對於Zn0.95Co0.05O薄膜的晶體結構、光學以及導電性質，以及經不同時間的高真空退火所造成的影響。希望對氫於多晶 Zn0.95Co0.05O薄膜中所扮演的角色能有更深入的了解。此研究中，混入氫氣於 Zn0.95Co0.05O 的薄膜成長中確實造成導電性，並且與摻入的含氫量成正比。由X光繞射結果可知，增加氫含量會擾亂多晶薄膜原本的 (002)優選取向，且晶面方向逐漸呈現隨機分布。由低略角X光繞射 fitting的結果可知微晶尺寸、晶胞體積也隨之縮減。穿透率圖中，摻氫量越多則樣品越暗淡越呈現金屬色，將此微分後可計算出光學帶隙與摻氫量幾乎呈線性增加。此值的上升可能是由於Burstein-Moss effect 所致。另外，我們由此圖中得出其晶相與非晶的相對含量百分比，與AFM表面得出的晶粒大小變化的趨勢有對應關係，並可觀察到此值於摻氫量30%之後逐漸上升，意味者其晶相含量逐漸變多且晶粒大小隨摻氫量的增長，讓晶粒間的晶界減少，也減少對載子的散射，這可能是導致在高度摻氫量中導電性較好的原因。而摻氫薄膜退火後造成導電性的上升，結晶度的提升，認為晶粒間的晶界變少以及因退火而增加的氧空缺是影響導電度上升的原因之一。此外，由MCD和穿透率量測皆觀察到Co2+ 原子確實取代了鋅原子的位置。由電阻對溫度的電性關係可得知導電的薄膜樣品皆屬於半導體性質。然而對其磁性的辨別、雜相和氧空缺的存在未來還需做更進一步的量測。

The roles of hydrogen induced defects in pure ZnO has been studied extensively. However, in a transition metal, such as Co, doped ZnO thin films the effect of hydrogen in electric conduction and magnetic coupling is still unclear and needs further study. Recently model predicts that hydrogen can be a shallow donor as well as an agent to induce ferromagnetism coupling between two adjacent Co ions which substitute the Zn sites at room temperature in a ZnO sample with a high Co doping ratio. However, the experimental supports is rare. In this study, Co-doped(5%) ZnO films are grown by a RF-magnetron sputtering system on glass substrate at room temperature. The growth condition is fixed for RF power in 200W, working press of 70 mtorr and various mixing ratio of H2/Ar+H2 gas. The crystal structure, electric and optical properties and the influence of vacuum annealing on the samples are studied. In this research, we found that the doping of hydrogen in Co-doped ZnO thin films truly increases the electric conductivity which is proportional to the H2/(Ar+H2) ratio. When the ratio of hydrogen is low, the (002) peak taken by a Glazing Angle X-ray Diffractometer dominates, while increasing hydrogen ratio other diffraction peaks appear, indicating an enhancement of crystal structure in all directions, and grain sizes and unit cell volume decrease. From the optical transmittance measurement, it is found that the color of films turned into metallic like and the optical band gap increases linearly with H2 ratio which can be attributed to the Burstein-Moss effect that corresponds to the increasing of carriers in the conduction band by doping of H2. The transmittance data provides the information of the ratio of crystalline and amorphous, which can also be correlated to the AFM results. When the H2 ratio is higher than 30%, more crystals and larger sizes of grains were formed in the films, such that carriers did not need to pass grain boundaries so frequently and experienced less scattering that was actually improve the electric conductivity. The electric conductivity can be even improved by post annealing in H2 environment. Moreover, the Magnetic circular dichroism (MCD) measurement shows that the Co2+ ions does truly substitute on Zn sited in Td symmetry during thin film deposition. The resistance measurement as a function of temperature found the hydrogenated Co-doped thin films are semiconductor conductive. More works are needed to determine the magnetization, identify second phases and Vo by SQUID and X-ray photoelectron spectroscopy.

Acknowledgement (致謝)-------------------------------------------------------------------ii
Abstract (Chinese) ---------------------------------------------------------------------------iii
Abstract (English) ---------------------------------------------------------------------------iv
Contents -----------------------------------------------------------------------------------------vi
Table List --------------------------------------------------------------------------------------viii
Figure List ------------------------------------------------------------------------------------viii

Chapter 1 Introduction-----------------------------------------------------------------------1
Chapter 2 Relevant Theory and Report-------------------------------------------------3
2-1 Background for ZnO--------------------------------------------------------------------3
2-1-1 Structure-----------------------------------------------------------------------------4
2-1-2 Defects in ZnO---------------------------------------------------------------------5
2-2 Diluted Magnetic Semiconductor (DMS) -----------------------------------------7
2-2-1 Predicament in Co-doped ZnO based DMS-----------------------------11
2-2-2 Hydrogen effects in Co-doped ZnO based DMS------------------------12
Chapter 3 Experiment Process and Equipment------------------------------------20
3-1 Experiment Process------------------------------------------------------------------20
3-1-1 Preparation of Co-doped ZnO target --------------------------------------20
3-1-2 Substrates Cleaning -----------------------------------------------------------21
3-1-3 The flow chart of whole process---------------------------------------------21
3-2 Equipment-------------------------------------------------------------------------------23
3-2-1 RF Magnetron Sputtering System-------------------------------------------23
3-2-2 X-ray Diffraction(XRD) ----------------------------------------------------------26
3-2-3 N&K Analyzer 1280--------------------------------------------------------------28
3-2-4 Atomic Force Microscope (AFM) ---------------------------------------------28
3-2-5 Magnetic Circular Dichroism (MCD) ----------------------------------------30
Chapter 4 Result and Discussion-------------------------------------------------------33
4-1 Effect of hydrogen incorporation in as-grown films---------------------------34
4-1-1 Transmittance---------------------------------------------------------------------35
4-1-2 X-ray diffraction--------------------------------------------------------------------40
4-1-3 Magnetic circular dichroism---------------------------------------------------45
4-1-4 Interim summary-----------------------------------------------------------------51
4-2 The Post annealing effect------------------------------------------------------------53
4-2-1 electric properties----------------------------------------------------------------54
4-2-2 Transmittance---------------------------------------------------------------------55
4-2-3 X-ray diffraction--------------------------------------------------------------------60
Chapter 5 Conclusion----------------------------------------------------------------------62
Reference--------------------------------------------------------------------------------------66
Appendix A-------------------------------------------------------------------------------------72
Appendix B-------------------------------------------------------------------------------------73




Table List

Table 4-1-1 Deposition conditions--------------------------------------------------------------------------------------------------------------------------------------------------------------33
Table 4-2-1 AFM 2D surface scan for 30~60% hydrogenated samples at different annealing time.-------------------------------------------------------------------------59


Figure List

Fig. 2-1 Two types of ZnO structures. (a) wurtzite and (b) zincblende, respectively.--------------------------------------------------------------------------------------------------------------------------------------------------------------4
Fig. 2-2 Formation enthalpy for various defects in ZnO that likely exists under Zn-rich and O-rich limit condition respectively.------------------------------------------------------------------------------------------------------7
Fig. 2-3 Computed values of the Curie temperature TC for various p-type semiconductors containing 5% of Mn percentage (2.5% per atom) and 3.5 × 1020 holes per cm3 (in 2002).-----------------------10
Fig. 2-4 Predicted Curie temperature as a function of lattice constant for a variety of semiconductors (from S.C. Erwin (Naval Research Laboratory) ).------------------------------------------------------------------10
Fig. 2-5 (a) ZnO wurtzite structure and the sites where interstitial hydrogen is introduced. BC indicates the bond-center sites, and AB indicates the antibonding sites. (b) Relaxation between positions of atomic hydrogen and host atoms in the BC configuration. Ideal lattice positions are shown in dotted lines.-------------------------------------------------------------------------------------------------------------------------14
Fig. 2-6 (a) Three-dimensional visualization of the hydrogen multicenter bonds in ZnO. (b) Formation energies as a function of the Fermi-level position for Hi, Vo and the multicenter bond configuration Ho in ZnO.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------14
Fig. 2-7 The interstitial H introduced into the sites of (a) Co-O BC configuration (HBC-Co) and the (b) (Co-H-Co) that is much stable than the former. (c) a simple band structure for the interstitial H deep level located at lower energy.----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------16
Fig. 2-8 The MCD signals of the hydrogenated Co-doped ZnO samples are dependent on the magnetic field at 13 K and 370 nm light wavelength.---------------------------------------------------------------------17
Fig. 2-9 XPS spectrums of Co-doped ZnO with Co= 5% and 9.1%, respectively. Both peak P1 and P4 indicate the Co metal state and Both P6 and P3 correspond to the shake-up satellite lines of P2 and P5 respectively. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------18
Fig. 2-10 Nuclear density distribution of Zn0.9Co0.1O powders (a) with and (b) without deuterium injection on the 5*10−3 fm/A3 isosurface obtained from the MEM and Rietveld analysis.-----------------19
Fig. 3-1 The flow chart of our experiment process.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------21
Fig. 3-2 Schematic diagram of RF magnetron sputtering system in Spintronics Lab, NSYSU. ---------------------------------------------------------------------------------------------------------------------------------------------24
Fig. 3-3 (a) A simplify RF system and (b) its AC signal versus time with 13.56 MHz.-----------------------------------------------------------------------------------------------------------------------------------------------------------25
Fig. 3-4 Two light wave scattered by two lattice planes with a path difference nλ or 2dsinθ. -------------------------------------------------------------------------------------------------------------------------------------------------27
Fig. 3-5 Photograph of N&K analyzer 1280.-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------28
Fig. 3-6 Vander Waals force and coulomb repulsion force in the vertical direction. ------------------------------------------------------------------------------------------------------------------------------------------------------------29
Fig. 3-7 The diagrams depict the origin of MCD signal.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------32
Fig. 4-1 Variation of sheet resistance with hydrogen contents for Co-dope ZnO thin films.---------------------------------------------------------------------------------------------------------------------------------------------------35
Fig. 4-2 Thicknesses of center region of thin films with different hydrogen concentrations.--------------------------------------------------------------------------------------------------------------------------------------------------35
Fig. 4-3 Optical images of the as-grown thin films. More H2 is introduced, more deep in the metallic look. From the left to right, the amount of H2 incorporated in sample is 10, 20, 30, 40, 50 and 60%, respectively.-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------36
Fig. 4-4 Transmittance of the hydrogenated Co-doped ZnO thin films. The right side picture shows zoomed part for 10~30% hydrogenated samples and the three known absorption features can be clearly observed.----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------37
Fig. 4-5 The plot of derivative transmittance curve shows clearly the existed peak 2 which implies the crystalline quality in the Co-doped ZnO thin films. The other, Peak 1, represent signal of the substrate (glass).---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------39
Fig. 4-6 AFM surface images of H2 incorporated conditions for H2 ratio within 10% ~60%.-------------------------------------------------------------------------------------------------------------------------------------------------39
Fig. 4-7 X-ray diffraction in GIXRD scanning. Besides, the elevation in the intensity after about 55o is resulted from instrument diffraction.----------------------------------------------------------------------------------41
Fig. 4-8 The fitting results (red one) for the GIXRD scan (black) with CCC filter crystal.-------------------------------------------------------------------------------------------------------------------------------------------------------43
Fig. 4-9 The Area ratio to the total area below the three main peaks of the hydrogenated Co-doped ZnO.------------------------------------------------------------------------------------------------------------------------------43
Fig. 4-10 The peak positions in angles obtained from the fitting results of the GIXRD scanning change with the H2/H2+Ar gas ratios.-----------------------------------------------------------------------------------44
Fig. 4-11 The peak positions in angles obtained from the fitting results of the GIXRD scanning change with the H2/H2+Ar gas ratios.-----------------------------------------------------------------------------------44
Fig. 4-12 a and c-axis lattice lengths for wurtzite lattice and corresponding unit cell volume as function H2/H2+Ar gas ratios.-----------------------------------------------------------------------------------------------45
Fig. 4-13 CD signals without applied magnetic field for hydrogenation (a)10%~30% and (b) 40%~60% for the Co-doped ZnO film.---------------------------------------------------------------------------------------47
Fig. 4-14 MCD signals with applied magnetic field of 7800 Gauss for hydrogenation (a) 10%~30% and (b) 40% ~60% for the Co-doped ZnO film.------------------------------------------------------------------48
Fig. 4-15 R-T measurements of Co-doped ZnO thin films with introduced H2 has shown a semiconducting-like property.---------------------------------------------------------------------------------------------------52
Fig. 4-16 Sheet resistance of the thin films after annealing by 0~15 mins for 40-60% hydrogenated samples. It holds almost same values before annealing and with the annealing time increasing, values start to separate each other, especially for 50% sample in 10 min.------------------------------------------------------------------------------------------------------------------------------------------------------------------------55
Fig. 4-17 Transmittance of hydrogenated Co-doped ZnO thin films (a) after annealing and (b) its derivative plots. All the scales is set to be the same.-------------------------------------------------------------56
Fig. 4-18 Optical band gaps after annealing for different times. It shows gaps are dropped quickly when the annealing process begins and saturates at a later time.-----------------------------------------57
Fig. 4-19 Variance in CA ratio (crystalline to amorphous) with gradually annealing time for 30~60% hydrogenated thin films.-----------------------------------------------------------------------------------------------58
Fig. 4-20 (a) GIXRD scan without CCC filter for 15min annealing. (b)Variance in Peak area ratio for (002) plane before and after 15 min annealing in different hydrogenated conditions.---------------61
Fig. 4-21 (a) GIXRD scan without CCC filter crystal for hydrogenated 60% sample before annealing. There is a small broad peak for Zn metal around ~42o and it obviously disappears in (b) after 15min annealing. Both scales in plots are set to be same.--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------61
Fig. 5-1 Various physical quantities of thin films versus different H2/Ar+H2 ratios. Among the figure, the CA ratio is crystalline to amorphous ratio calculated from transmittance spectrum.----------------63
Fig. 5-2 The illustration of the hydrogenated dynamics in the Co-doped ZnO films.------------------------------------------------------------------------------------------------------------------------------------------------------------64
Fig. A The XRD diffraction pattern for pure ZnO powder with 1.5406 A in x-ray wavelength.------------------------------------------------------------------------------------------------------------------------------------------------72
Fig. B-1 O K-edge XANES spectra of Zn1−xCoxO (x=0.005, 0.02) thin films, ZnO powder, and the calculated spectra for different structure models by replacing one, two, three, and four Zn nearest neighbors of the absorbing O atom with Co.----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------74
Fig. B-2 (a) O K-edge XANES spectra of Zn0.95Co0.05O sample, and the calculated spectra for different structural models by replacing one, two, three, and four the nearest Zn neighbors of Coo with Co atoms. (b) O K-edge XANES spectra of CoyZn1-yO (y=0.20, 0.25) samples, and the calculated spectra for different structural models by placing one Zni atom inside the nearest neighbors, and replacing one, two, three and four the nearest Zn neighbors of CoS with Co atoms[50]. Those calculations had been achieved by FEFF8.2.--------------------------------------------------------------------------------74
Fig. B-3 The x-ray absorption spectrum of our samples from 10% to 60% hydrogenation. The results are all normalized to original x-ray incident light (I0) and take an intensity averaged from 565 to 569 eV as an reference.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------76
Fig. B-4 The highest intensity of peak A1 and C obtained from Fig. B-3 for different hydrogenation from 10% to 60%.---------------------------------------------------------------------------------------------------------------77

[1] C. Woll, “ The chemistry and physics of zinc oxide surfaces ”, Progress in Surface Science 82, 55 (2007).
[2] U. Ozgur, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho and H. Morkoc, “ A comprehensive review of ZnO materials and devices ”, J. Appl. Phys. 98, 041301 (2005).
[3] O. Madelung, U. Rossler, M. Schulz (Eds.), Landolt-Bornstein, NewSeries, Group III, 17B, 22a, 41B, Springer, Heidelberg (2006).
[4] Y. Yan, S. B. Zhang, and S. T. Pantelides, “ Control of Doping by Impurity Chemical Potentials: Predictions for p-Type ZnO ”, Phys. Rev. Lett. 86, 5723 (2001).
[5] C. H. Park, S. B. Zhang and Su-Huai Wei, “ Origin of p-type doping difficulty in ZnO: The impurity perspective ”, Phys. Rev. B 66, 073202 (2002).
[6] S. B. Zhang, S.-H. Wei, and Alex Zunger, “ Intrinsic n-type versus p-type doping asymmetry and the defect physics of ZnO ”, Phys. Rev. B 63, 075205 (2001).
[7] Mukul Agrawal, “ Magnetic Properties of Materials, Dilute Magnetic Semiconductors, Magnetic Resonances and Spintronics ”, http://www.stanford.edu/~mukul/tutorials, 42.
[8] T. Dietl, “ Ferromagnetic semiconductors ”, Semicond. Sci. Technol. 17, 377 (2002).
[9] K. Potzger, “ High cluster formation tendency in Co implanted ZnO ”, J. Appl. Phys. 104, 023510 (2008).
[10] J. Okabayashi, K. Ono, M. Mizuguchi, M. Oshima, Subhra Sen Gupta, D. D. Sarma, T. Mizokawa, A. Fujimori, M. Yuri, C. T. Chen, T. Fukumura, M. Kawasaki, and H. Koinuma, “ X-ray absorption spectroscopy of transition-metal doped diluted magnetic semiconductors Zn1−xMxO ”, J. Appl. Phys. 95, 3573 (2004).
[11] S. Datta and B. Das, “ Electronic analog of the electro‐optic modulator ”, Appl. Phys. Lett. 56, 665 (1990).
[12] F.Matsukura, “ Transport properties and origin of ferromagnetism in (Ga,Mn)As ”, Phys. Rev. B 57, 2037 (1998).
[13] H. Munekata, H. Ohno, S. von Molnar, Armin Segmuller, L. L. Chang, and L. Esaki, “ Diluted magnetic III-V semiconductors ”, Phys. Rev. Lett. 63, 1849 (1989).
[14] S. J. Pearton, D. P. Norton, M. P. Ivill, A. F. Hebard, J. M. Zavada, W. M. Chen and I. A. Buyanova, “ Ferromagnetism in Transition-Metal Doped ZnO ”, J Electron Mater, 36, 462 (2007).
[15] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, “ Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors ”, Science 287, 1019 (2000).
[16] Jian-jun Li, Wei-chang Hao, Huai-zhe Xu, and Tian-min Wang, “ Variation of structural and magnetic properties with Co-doping in Zn1−xCoxO nanocrystals ”, J. Appl. Phys. 105, 053907 (2009).
[17] D. J. Norris, A. L. Efros, and S. C. Erwin, “ Doped Nanocrystals ”, Science 319, 1776 (2008).
[18] G. M. Dalpian and J. R. Chelikowsky, “ Self-Purification in Semiconductor Nanocrystals ”, Phys. Rev. Lett. 96, 226802 (2006).
[19] C. G. Van. de. Walle, “ Hydrogen as a Cause of Doping in Zinc Oxide ”, Phys. Rev. Lett. 85, 1012 (2000).
[20] V. Lavrov, J. Weber, F. Borrnert, C. G. Van de Walle, and R. Helbig, “ Hydrogen-related defects in ZnO studied by infrared absorption spectroscopy ”, Phys. Rev. B 66, 165205 (2002).
[21] A. Janotti and C. G. Van de Walle, “ Hydrogen multicenter bonds ”, Nat. Mater. 6, 44 (2007).
[22] C. H. Park, D. J. Chadi, “ Hydrogen-Mediated Spin-Spin Interaction in ZnCoO ”, Phy. Rev. Lett. 94 127204 (2005).
[23] H.-J. Lee, C. H. Park, and S.-Y. Jeonga, “ Hydrogen-induced ferromagnetism in ZnCoO ”, Appl. Phys. Lett. 88, 062504 (2006).
[24] Su Jae Kim, Seunghun Lee, Yong Chan Cho, Y. N. Choi, S. Park, I. K. Jeong, Yoshihiro Kuroiwa, Chikako Moriyoshi and Se-Young Jeong, “ Direct observation of deuterium in ferromagnetic Zn0.9Co0.1O:D ”, Phys. Rev. B. 81, 212408 (2010).
[25] 曹耀中: “ 氧化鋅摻鈷之稀磁性氧化物薄膜之成長與物性研究 ”，國立中山大學物理所，2010。
[26] Physics of Thin Films, “http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/sputtertech.htm”.
[27] 億達薄膜股份有限公司: “ http://www.etafilm.com.tw/PVD_Sputtering_Deposition_ch.html ”。
[28] X-ray scattering techniques, “ http://en.wikipedia.org/wiki/X-ray_scattering_techniques ”。
[29] 楊孟璇: “ 低溫濺鍍非晶相ZnO:Al 薄膜之研究 ”，國立中山大學物理研究所，2009。
[30] L. Eckertova and T. Ruizicka, “ Diagnostics and Applications of Thin Films ”, Institute of Physics Publishing , 1993.
[31] 陳哲雄，林俊勳，林紋瑞，吳靖宙: “ 原子力顯微鏡成像原理與中文簡易操作手冊 ”，成功大學醫學工程所生醫感測實驗室。
[32] Mason, W. Roy, “ A Practical Guide To Magnetic Circular Dichroism Spectroscopy ”, John Wiley & Sons Inc (2007).
[33] J. R. Neal, A. J. Behan, R. M. Ibrahim, H. J. Blythe, M. Ziese, A. M. Fox, and G. A. Gehring, “ Room-Temperature Magneto-Optics of Ferromagnetic Transition-Metal-Doped ZnO Thin Films ”, Phys. Rev. Lett. 96, 197208 (2006).
[34] P. Koidl, “ Optical absorption of Co2+ in ZnO ”, Phys. Rev. B 15, 2493 (1977).
[35] K. Ando, H. Saito, Zhengwu Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto, and H. Koinuma, “ Large magneto-optical effect in an oxide diluted magnetic semiconductor Zn1−xCoxO ” , Appl. Phys. Lett. 78, 2700 (2001).
[36] Y. Fukuma, H. Asada, J. Yamamoto, F. Odawara, and T. Koyanagi, “ Large magnetic circular dichroism of Co clusters in Co-doped ZnO ”, Appl. Phys. Lett. 93, 142510 (2008).
[37] B. L. Zhu, J. Wang, S. J. Zhu, J. Wu, R. Wu, D. W. Zeng, C. S. Xie, “ Influence of hydrogen introduction on structure and properties of ZnO thin films during sputtering and post-annealing ” , Thin Solid Films, 519, 3809 (2011).
[38] N. Volbers, H. Zhou, C. Knies, D. Pfisterer, J. Sann, D.M. Hofmann and B.K. Meyer, “ Synthesis and characterization of ZnO: Co2+ nanoparticles ”, Appl. Phys. A 88, 153–155 (2007).
[39] Y.S. Kang, H.Y. Kim, J.Y. Lee, “ Effects of hydrogen on the structural and electro-optical properties of zinc oxide thin film ”, J. Electrochem. Soc. 147, 4625 (2000).
[40] Dong-Ho Kim, et al., “ Effects of deposition temperature on the effectiveness of hydrogen doping in Ga-doped ZnO thin films ”, J. Appl. Phys. 108, 023520 (2010).
[41] Weifeng Liu, Guotong Du, Yanfeng Sun, Yibin Xu, Tianpeng Yang, Xinsheng Wang, Yuchun Chang and Fabin Qiu, “ Al-doped ZnO thin films deposited by reactive frequency magnetron sputtering: H2-induced property changes ” , Thin Solid Films, 515, 3057 (2007).
[42] Jeng-Lin Chung, Jyh-Chen Chen and Chung-Jen Tseng, “ Preparation of TiO2-doped ZnO films by radio frequency magnetron sputtering in ambient hydrogen–argon gas ” , Appl. Surf. Sci. 255, 2494 (2008).
[43] S. J. Tark, Y.-W. Ok, M. G. Kang, H. J. Lim, W. M. Kim and D. Kim, “ Effect of a hydrogen ratio in electrical and optical properties of hydrogenated Al-doped ZnO films ” , Electrochem, 23, 548 (2009).
[44] J. B. Webb, D. F. Williams and M. Buchanan, “ Transparent and highly conductive films of ZnO prepared by RF reactive magnetron sputtering ”, Appl. Phys. Lett. 39, 640 (1981).
[45] J. Čižek, N. Žaludova, M. Vlach, S. Daniš, J. Kuriplach, I. Prochazka, G. Brauer, W. Anwand, D. Grambole, W. Skorupa, R. Gemma, R. Kirchheim, A. Pundt, “ Defect studies of ZnO single crystals electrochemically doped with hydrogen ”, J. Appl. Phys. 103, 053508 (2008).
[46] C. G. Van de Walle, “ Hydrogen as a cause of doping in ZnO ”, Phys. Rev. Lett. 85, 1012 (2000).
[47] Dong-Ho Kim, Sung-Hun Lee, Gun-Hwan Lee, Hyun-Bum Kim, Kwang Ho Kim, Yoon-Gyu Lee and Tae-Hwan Yu, “ Effects of deposition temperature on the effectiveness of hydrogen doping in Ga-doped ZnO thin films ”, J. Appl. Phys. 108, 023520 (2010).
[48] M. Toyoda, H. Akai, K. Sato, H. Katayama-Yoshida, “ Electronic structures of (Zn,TM)O (TM: V, Cr, Mn, Fe, Co, and Ni) in the self-interaction-corrected calculations ”, Physica B 376–377, 647–650 (2006).
[49] Zhihu Sun, Wensheng Yan, Guobin Zhang, Hiroyuki, Oyanagi, Ziyu Wu, Qinghua Liu, Wenqing Wu, Tongfei Shi, Zhiyun Pan, Pengshou Xu, and Shiqiang Wei, “ Evidence of substitutional Co ion clusters in Zn1−xCoxO dilute magnetic semiconductors ” , Phys. Rev. B 77, 245208 (2008).
[50] Tongfei Shi, Yuqi Wang, Zhijun Yin, Yunpeng Zhang and Shishen Yan, “ Study of the O K-edge XANES of Cobalt-doped ZnO diluted magnetic semiconductors ”, J. Phys.: Conf. Ser. 193, 012099 (2009).
[51] O Šipr and F Rocca, “ Zn K edge and O K edge x-ray absorption spectra of ZnO surfaces: implications for nanorods ”, J. Phys.: Condens. Matter 23, 315501 (2011).
[52] E. C. Lee and K. J. Chang, “ Ferromagnetic versus antiferromagnetic interaction in Co-doped ZnO ”, Phys. Rev. B 69, 085205 (2004).