本論文研究以原子層沉積法在低溫直接成長氧化鋅薄膜在(0001)面氧化鋁基板上。實驗採用二乙基鋅及氧化亞氮分別做為鋅及氧原子之前驅物，並以高度純化之氮氣做為傳輸氣體。原子層沉積系統的自限式製程條件在二乙基鋅的部份流量區域可以達成。自限式試窗在基板溫度為290oC到310oC之間也可觀察到。氧化鋅薄膜之微結構特性、光吸收現象、電性及表面形態分別使用X-光繞射分析、掃描式電子顯微術、穿透光譜分析、原子力顯微術及霍爾量測來鑑定。對於藉由控制原子層沉積法反應循環次數以改變生長厚度於300oC之氧化鋅薄膜，及改變沉積溫度以探討氧化鋅薄膜特性之變化，也都有相關之實驗結果做討論。

In this thesis, low temperature (LT) ZnO films were directly grown on (0001) sapphire substrates by atomic layer deposition (ALD) using diethylzinc (DEZn) and nitrous oxide (N2O) as source precursors. Purified N2 was utilized to serve as carrier gas. Self-limiting window of ALD was achieved for a certain range of DEZn flow rate. Self-limiting window was also observed for a substrate temperature ranging from 290 to 310oC. The structural, electrical and morphological characteristics of ZnO films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance spectroscopy, atomic force microscopy and Hall measurements. The influences of film thickness on the transport characteristics of the ALD-grown ZnO film are also presented.

Abstract (in Chinese)……………………………………………………..i
Abstract ………………………………………………………………….ii
Table of contents………………………………………………………...iii
List of tables……………………………………………………………...v
List of figures……………………………………………………………vi
Chapter 1 Introduction……………………………………………………1
Chapter 2 Background……………………………………………………3
2-1 The property of ZnO……...……………………………….3
2-2 Optical property of ZnO…………………………………...9
2-3 The lattice mismatch between ZnO film and sapphire substrate………………………………………………....11
2-4 Fundamental aspects of ALD…………………………….15
Chapter 3 Experimental procedures
3-1 Substrate cleaning………………………...……………...18
3-2 Growth of ZnO films……………………………………..20
3-2.1 The self-limiting window of ZnO using DEZn and N2O………………………………………………...21
3-2.2 ZnO films grown with various ALD cycles………..21
3-2.3 ZnO films grown with various substrate temperatures
……………………………………………………..21
3-3 Characterization…………...……………………………..27
3-3.1 X-ray diffraction……………………………………27
3-3.2 Scanning electron microscopy …………………….27
3-3.3 Absorption spectroscopy…………………………...28
3-3.4 Atomic force microscopy…………………………..28
3-3.5 Hall effect measurement……………………...…….28

Chapter 4 Result and discussion
4-1 Growth and characterization of ZnO films on (0001) sapphire substrates…...……………………..……...……35
4-2 Influence of the number of ALD cycle on the morphology
of a ZnO film……………………………..……………44
4-3 Characterization of ZnO films grown at various deposition temperatures……………..………………………………53
Chapter 5 Conclusions…………………………………………………..61
Reference…………………………………………………………………..62

List of tables

Table 1 A list of the FWHM of The (0002) diffracted peaks under various DEZn flow rates……………………………………………….40
Table 2 List of mean ZnO grain sizes and FWHM of (0002) ZnO XRD signals………………………………………………………….55

List of figures

Fig.2-1 A plot of the wurtzite structure of ZnO…………………………4
Fig.2-2 A simplified E-k relationship of a direct band gap semiconductor
…………………………………………………………………....5
Fig.2-3 A plot of the calculated energy levels of defects in ZnO………...6
Fig.2-4 A plot of the calculated energy levels of defects in ZnO………...7
Fig.2-5 A plot of the intrinsic defects in ZnO……………………………8
Fig.2-6 Schematic of a unit cell of the wurtzite structure showing c, a and
r plane………………………………………………………….12
Fig.2-7 The atomic arrangements of a c-plane ZnO film grown on the c-plane sapphire substrate……………………………………...13
Fig.2-8 A schematic lattice structure of an epilayer grown on mismatched substrate…………………………………………………………14
Fig. 2-9 A schematic diagram shown ALD of one monolayer of an AB compound……………………………………………………...17
Fig. 3-1 A flow chart of substrate cleaning procedures………………....19
Fig. 3-2 A schematic diagram of the home-made ALD system……...…22
Fig. 3-3 A schematic of the ZnO films with various DEZn flow rates….23
Fig. 3-4 A schematic of the ZnO films with various deposition temperatures…………………………………………………….24
Fig.3-5 A schematic of the ZnO films with different ALD cycles……...25
Fig.3-6 A schematic of the ZnO films with different temperatures……..26
Fig. 3-7A schematic diagram of X-ray diffractometer……………….…31
Fig.3-8 A schematic diagram of UV-Vis spectrometer…………………32
Fig.3-9 A schematic diagram of atomic force microscopy……………..33
Fig.3-10 Typical geometric figure for Hall Effect measurement……….34
Fig. 4-1 The growth rate of ZnO films with different DEZn flow rates...37
Fig. 4-2 The growth rates of ZnO films at various substrate
temperatures……………………………………………………38
Fig. 4-3 Typical θ-to-2θ X-ray diffraction spectra of ZnO films with
different DEZn flow rates………………………………….…..39
Fig. 4-4 FESEM micrographs of the ZnO films grown on (0001) sapphire substrates with DEZn flow rates being (a) 1.91, (b) 3.81, (c)5.72, (d)6.87, (e) 7.63, (f) 8.77, (g)9.53 and (f)11.44 μmol/min, respectively…………………………………………………….41
Fig. 4-5 Optical transmittance of ZnO films grown at 300 ℃ with the DEZn flow rates being within self-limiting window…………..42
Fig. 4-6 Plots of (αhν)2 versus photon energy (hν) for ZnO films grown under different DEZn flow rates……………………………….43
Fig. 4-7 The thickness of a ZnO films as a function of number of growth cycle……………………………………………………………46
Fig. 4-8 Typical θ-to-2θ X-ray diffraction plots of ZnO films haveing different ALD cycles…………………………………………..47
Fig. 4-9 FESEM morphologies of ZnO films prepared by ALD with the number of growth cycle being (a)600 (b) 900 (c) 1200 (d)1500, respectively…………………………………………………….48
Fig. 4-10 AFM image of a 2×2 μm2 area of ZnO films with (a)600 (b)900 (c)1200 (d)1500 cycles……………………………………...49
Fig. 4-11 Resistivity, electron concentration and mobility of ZnO films prepared at different ALD cycles………………………...……50
Fig. 4-12 Plots of the transmission spectra of ZnO films with different thicknesses………………………………………………..…..51
Fig. 4-13 Plots of (αhν)2 versus photon energy (hν) for ZnO films with different ALD cycles…………………………………………52
Fig.4-14 Typical θ-to-2θ X-ray diffraction spectra of ZnO films grown at various temperatures…………………………………55
Fig. 4-15 FESEM images of ZnO films grown at different substrate temperatures……………………………………………………56
Fig. 4-16 AFM images of a 2×2 μm2 area of ZnO films grown at substrate temperatures at (a)250, (b)300 and (c)350 oC………………57
Fig. 4-17 Resistivity, electron concentration and mobility of a ZnO film grown 250, 300, 350 oC………………………………………58
Fig. 4-18 Optical transmittance of ZnO films prepared at various substrate temperatures………………………………………..59
Fig. 4-19 Plots of (αhν)2 versus photon energy (hν) for ZnO films prepared at various substrate temperatures………………...…60

[1] K. Tamura,A. Ohtomo, Y. Osaka, T. Makino, Y. Segawa, M. Sumiya,
S. Fuke, H. Koinuma, and M. Kawasaki, J. Cryst. 214/215, 59
(2000).
[2] Y. Chen , H. Ko, S. Hong, T. Yao, and Y. Segawa, J. Cryst. 214/215,
87 (2000).
[3] X. Liu, X. Wu, H. Cao, and R.P.H. Chang, Jour. Appl. Phys. 95, 15 (2004)
[4] Xuhu Yu, Jin Ma, Feng Ji, Yuheng Wang, Xijian Zhang, Chuanfu Cheng, Honglei Ma, Applied Surface Science 239 (2005) 222
[5] K.Y. Cheong, N. Muti, S. Roy Ramanan, Thin Solid Films 410 (2002) 142.
[6] S. Liu, J.J. Wu, Mater. Res. Soc. Symp. Proc. 703 241 (2002).
[7] H. Tampo, A. Yamada, P. Fons, H. Shibata, K. Matsubara, K. Iwat, S. Niki, Appl. Phys. Lett. 84, 4412 (2004).
[8] A. Sasaki, W. Hara, A. Matsuda, N. Tateda, S. Otaka S. Akiba Appl. Phys. Lett. 86, 231911 (2005).
[9] J.R. Gong, D. Jung, N.A. El-Masry, and S.M. Bedair Appl. Phys. Lett 57, 400 (1990)
[10] B. Lin, Z. Fu and Y. Jia Appl. Phys. Lett. 79, 07934 (2001).
[11] E. G. Bynlander, J. Appl. Phys. 49, 1188 (1978).
[12] R. Dingle, Phys. Rev. Lett. 23, 579 (1969).
[13] D. C. Reynolds, D. C. Look, B. Jogai, and H. Morkoc, Solid State
[14] Y. W. Heo, K. Ip, S. J. Pearton, D. P. Norton, J. D. Budia, Appl. Surf. Sci. 252 7442-7448 (2006).
[15] L. E. Greene, M. Law, J. Goldberger, F. Kim, J. C. Johnson, Y. Zhang, R. J. Saykally, and P. Yang, Angew. Chem. Int. Ed. 42, 3031 (2003).
[16] S. A. Studenikin, N. Golego, and M. Cocivera, J. Appl. Phys. 84, 2287(1998).
[17] E. Ziegler, A. Heinrich, H. Oppermann, and G. Stover, Phys. Status Solidi A 66, 635 (1981).
[18] E. Burstein, “Anomalous Optical Absorption Limit in InSb”, Phys. Rev.,93(1954) p.632-633.
[19] T. S. Moss, “The Interpretation of the Properties of Indium Antimonide”, Phys. Soc. London Sect. B, 67(1954) p.775-782.
[20] J. Chen, and T. Fujita, Jpn. J. Appl. Phys. 42 602 (2003).
[21] B. P. Zhang, N. T. Binh, Y. Segawa, Y. Kashiwaba, and K. Haga,
Appl. Phys. Lett. 84 586 (2004).
[22] C. R. Gorla, N. W. Emanetoglu, S. Liang, W. E. Mayo, Y. Lu, M.
Wraback and H. Shen, J. Appl. Phys. 85 2595 (1999).
[23] D. A. Neamen, SEMICONDUCTOR PHYSICS AND DEVICES: Basic Principles, nd ed., McGraw-Hill Companies, USA, 1997
[24] Jongmin Lim, Chongmu Lee, J. Alloys and Compounds 449 (2008) 371–374