在本篇論文中，我們在300oC使用原子層沉積法直接在(01-12)氧化鋁基板上沉積氧化鋅薄膜，並且分別使用二乙基鋅和氧化亞氮做為二族和六族的前驅物。接著探討在不同參數下退火之氧化鋅薄膜的特性，包含不同退火溫度、不同退火時間、不同退火氣氛。氧化鋅薄膜的結構、光學性質和電性分析，我們分別使用X-光繞射儀，場發射掃描式電子顯微術，霍爾量測，光激發光量測和原子力顯微術。依據X-光繞射的結果，氧化鋅薄膜皆顯現出c-軸的優選方向。我們發現經過退火後的氧化鋅薄膜的電性和結構與退火氣氛有很大的關聯性。在本實驗中，我們發現氧化鋅薄膜在氮氣氣氛下退火十分鐘可以有效的改善薄膜的光穿透特性和電性。在此條件下，可得到較高的光學穿透率(~87%)，較低的電阻率(~1.12x10-2 Ω∙cm) 和較高的電子移動率(~17.20 cm2/Vs)。

In this thesis, low temperature (RT) zinc oxide (ZnO) films were directly grown on (01-12)sapphire substrates at 300oC by atomic layer deposition (ALD) using diethylzinc (DEZn) and nitrous oxide (N2O). Influences of post-annealing parameters including annealing temperature, annealing time interval and annealing atmosphere on the properties of post-annealing ZnO films were investigated. The structural, optical and transport properties of the post-annealing ZnO films were characterized by θ-to-2θ X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Hall measurements, photoluminescence spectroscopy (PL) and atomic force microscopy (AFM). Based on the XRD results, ZnO films were found to show c-axis preferred orientation. It was found that the transport and structural properties of the ZnO post-annealed films were highly influenced by annealing atmosphere. The most significant improvement in structural and transport properties were obtained for the ZnO film annealed in in N2 atmosphere at 900 oC for 10min. Under the optimum annealing condition, high transparency (~87%), low resistivity of 1.12x10-2 Ω∙cm and high mobility of 17.20 cm2/Vs were achieved in the ZnO films.

Table of Contents
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 Physical properties of ZnO …................................................3
2-2 Substrates for current ZnO epitaxy ........................................7
2-3 Fundamental aspects of ALD ................................................8

Chapter 3 Experimental procedures ...........................................................11
3-1 Substrate cleaning ................................................................11
3-2 Growth of ZnO films .......….…...........................................12
3-2.1 ZnO films deposited with different DEZn flow rates………………………………………………….12
3-2.2 ZnO films annealed at different temperatures in N2 atmosphere for 5min……………………………....... 13
3-2.3 ZnO films annealed with different time intervals at 900oC in N2 atmosphere…..........................................13
3-2.4 ZnO films annealed in N2, N2O and N2/N2O atmospheres ...............................................................13
3-3 Characterization methods …................................................17
3-3.1 X-ray diffraction .........................................................17
3-3.2 UV-Vis spectrometer ..................................................17
3-3.3 Photoluminescence spectroscopy................................18
3-3.4 Scanning electron microscopy.....................................19
3-3.5 Atomic force microscopy (AFM) ...............................19
3-3.6 Van der Pauw Hall measurement …………................20

Chapter 4 Results and discussion …....………...…………………………25
4-1 ZnO films deposited with different DEZn flow rates...........25
4-2 Influence N2 annealing on the properties of ZnO films growth on sapphire substrates….............................................36
4-3 ZnO films post-annealed for different time intervals at 900oC in N2 atmosphere....................................................................50
4-4 ZnO films annealed in N2 and/or N2O atmosphere...............58

Chapter 5 Conclusions………………………….…………………………65

Reference.....................................................................................................66














List of tables
Table4-1 A list of the thicknesses of ZnO films being deposited at 300oC with different DEZn flow rates………………………………...28

Table4-2 A list of the properties of as-deposited ZnO films with different DEZn flow rates………………………………………………..30

Table4-3 A list of the RT transport data of the as-deposited ZnO films grown at different DEZn flow rates…………………………….35

Table4-4 A list of the properties of as-deposited and post-annealed ZnO
films…………………………………………………………….42

Table4-5 A list of the transport data of as-deposited and post-annealed ZnO
films…………………………………………………………….46

Table4-6 A list of the properties of post-annealed ZnO films under N2 ambient for different time intervals…………………………….55

Table4-7 A list of transport data of the post-annealed ZnO films under N2
ambient for different time intervals………………………..…...55

Table4-8 A list of the properties of annealed ZnO films in N2, N2O and N2/N2O ambients……………………………………………….62

Table4-9 A list of transport data of the annealed ZnO films in N2, N2O and N2/N2O ambients……………………………….………………62









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……………………………………………………...4

Fig.2-3 A plot of the calculated energy levels of defects in ZnO ……...….5

Fig.2-4 A plot of the calculated energy levels of defects in ZnO……….....5

Fig.2-5 Intrinsic defects in ZnO…………………………………………....6

Fig.2-6 A schematic showing c-, a- and r-plane within the hexagonal
unit cell……………………………………………………………..7

Fig.2-7 A schematic diagram of epitaxial growth of an AB compound by
ALD process……………………………………………………....10

Fig.3-1 A schematic of the home-made ALD system at NCHU……….....14

Fig.3-2 A plot of the temperature versus time process for ZnO films
deposited with different DEZn flow rates…………………...……15

Fig.3-3 A plot of the temperature versus time process for ZnO films
annealed at different temperatures in N2 atmosphere for 5min...…15

Fig.3-4 A plot of the temperature versus time process for ZnO films annealed with different time intervals at 900oC in N2 atmosphere………………………………………………………...16

Fig.3-5 A plot of the temperature versus time process for ZnO films annealed in N2 , N2O, and N2/N2O atmospheres………………….16

Fig.3-6 A schematic diagram of an X-ray diffractometer…………...……21

Fig.3-7 A diagram of the components in a UV-vis spectrophotometer…...22
Fig.3-8 A plot of the components of the PL measurement system………..23

Fig.3-9 A diagram of Atomic Force Microscope……………………...….24

Fig.4-1 A list of ZnO growth rate versus on DEZn flow rate……...……..28

Fig.4-2 Typical θ-to-2θ x-ray diffraction plots of the as-grown ZnO films on sapphire substrates with DEZn flow rate being (a)5.72, (b)7.63, (c)8.78, (d)10.68, (e)11.45 μmole/min, respectively.….29

Fig.4-3 Plots of the transmission spectra of the ZnO films grown at different DEZn flow rates……………..…………………..……..31

Fig.4-4 Plots of (αhυ)2 versus photon energy of ZnO films grown at different DEZn flow rates…..……………………………………32

Fig.4-5 SEM images of the ZnO films on sapphire substrates with DEZn flow rate being (a)5.72, (b)7.63, (c)8.78, (d)10.68, (e)11.45 μmole/min, respectively………………………..………..33

Fig.4-6 AFM images of the surface morphologies of ZnO films prepared in the self – limiting regime with DEZn flow rates being (a) 7.63, (b)8.78 and (c)10.68μmole/min, respectively……….……………34

Fig.4-7 Typical θ-to-2θ x-ray diffraction plots of the post-annealed ZnO films grown on sapphire substrates. (a)As-deposited and post-annealed at (b)800oC, (c)850oC, (d)900oC, (e)950oC and (f)1000oC in N2 atmosphere………………………………………40

Fig.4-8 Plots of FWHM of the XRD ZnO (0002) peak and ZnO grain sizes of the films versus annealing temperature……………………..….41

Fig.4-9 Plots of the transmittance of ZnO films in UV-Vis IR regions
before and after annealing at various temperatures under N2 atmosphere……………………………………………………...43

Fig.4-10 Plots of (αhυ)2 versus photon energy for ZnO films post-annealed at different temperatures in N2 atmosphere…………………….44

Fig.4-11SEM images of the ZnO films post-annealed under N2 ambient at different temperatures for 5min. (a)As-deposited and post-annealed (b)at 800oC, (c)at 850 oC, (d)at 900 oC, (e)at 950 oC and (f)at 1000 oC………………………………………………....45

Fig.4-12 Plots of electron concentration, Hall mobility, and resistivity of ZnO films as functions of annealing temperatures…………..…..47

Fig.4-13 RT PL spectra of ZnO films post-annealed at different temperatures for 5 min in N2 atmosphere………..………………48

Fig.4-14 Plots of intensity, peak position and FWHM of the RT NBE PL of the post-annealed ZnO films versus annealing temperatu………49

Fig.4-15 Typical θ-to-2θ x-ray diffraction plots of the ZnO films post-annealed at 900oC for (a)5min and (b)10min in N2 atmosphere....................................................................................52

Fig.4- 16 Plots of the transmittance spectra of ZnO films post-annealed at 900oC for different time intervals in N2 atmosphere…………….53

Fig.4-17 Plots of (αhυ)2 versus photon energy for ZnO films post-annealed at 900oC in N2 atmosphere………………………….…………..54

Fig.4-18 SEM images of ZnO films after post-annealing at 900oC in N2 atmosphere (a)900oC for 5 min and (b)900oC for 10 min…….…56

Fig.4-19 Plot of the RT PL spectra of ZnO films post-annealed at 900oC for different time intervals in N2 atmosphere………………………..57

Fig.4-20 Typical θ-to-2θ x-ray diffraction plots of the post-annealed ZnO films (a) at 900oC for 10min in N2 atmosphere, (b) at 900oC for 10min in N2O atmosphere , (c)at 900oC for 10min in N2 atmosphere and then at 600oC for 1 hr in N2O atmosphere…………………………………………….…..……..59
Fig.4-21 Plots of the transmission spectra of ZnO films after annealing in N2, N2O and N2/N2O ambient, respectively……………………..60

Fig.4-22 Plots of (αhυ)2 versus photon energy for ZnO films post-annealed in N2, N2O and N2/N2O ambient, respectively…………….…….61

Fig.4-23 SEM images of ZnO films after post-annealing (a) at 900oC in N2 atmosphere for 10 min, (b) at 900oC in N2O atmosphere for 10 min and (c) at 900oC in N2 atmosphere for 10 min and then at 600oC in N2O atmosphere for 1 hr……………………….………………..63

Fig.4-24 Plots of RT NBE PL spectra of ZnO films annealed at 900oC for different time intervals in N2, N2O and N2/N2O ambient, respectively……………………………………………………....64

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