臺灣博碩士論文加值系統

本論文以使用原子層沉積技術製備的超薄（小於50奈米）氧化鋅薄膜為主軸，研究其摻雜鋁以後之傳輸特性，以及其成長在矽奈米柱基板上所顯現之室溫鐵磁特性。在電傳輸特性的部份，我們將一系列厚度為~30奈米的摻鋁氧化鋅藉由原子層沉積技術成長在矽(100)基板上，以探討溫度效應對晶格方向、穿透率、以及光電特性上的影響。本實驗特別利用臨場摻雜方式，在100到300 ℃之間成長摻鋁氧化鋅薄膜，以提升鋁摻雜的效應。實驗結果顯示，提高生長溫度會提升薄膜的結晶性和載子遷移率，以及可見光範圍內的平均穿透率皆高於95%。尤其是在成長溫度為300 ℃的樣品，雖然其電阻率(6×〖10〗^(-4) Ω-cm)比使用濺鍍方式(2~4×〖10〗^(-4) Ω-cm)來的高，但是其遷移率(136 cm^2 V^(-1) s^(-1))比之前的文獻(50~60 cm^2 V^(-1) s^(-1))提升了2倍有餘。二次離子質譜儀分析顯示氫原子的鍵結可以有效減少界面電荷陷阱密度,可能是進一步導致了載子遷移率增加的主要關鍵。本研究結果顯示摻鋁氧化鋅薄膜，在光電元件的應用上是極具有競爭力的。有關室溫鐵磁特性部分的研究，主要想進一步釐清目前學界對有關未摻雜過渡金屬的氧化物半導體顯現室溫鐵磁性的真正原因。本實驗設計，將一系列氧化鋅薄膜藉由原子層沉積技術，分別成長在矽(100)基板以及矽奈米柱上，並藉由成長溫度控制薄膜中的缺陷種類與濃度，以觀察其對顯現之室溫鐵磁性的影響，以進一步分析導致室溫鐵磁性的主要原因。光激發螢光光譜以及X射線光電子能譜指出低溫成長的氧化鋅具有較多的缺陷，而根據超導量子干涉磁量儀量測結果顯示，這些具較高濃度缺陷的薄膜均具有較高的飽和磁化強度(1.76 emu/cm^3)且其鐵磁轉變之居禮溫度可高達404K。進一步分析指出，未摻雜氧化鋅薄膜的鐵磁性，主要源自於單價電荷氧空缺與鋅缺陷之間的交互作用。而成長在矽奈米柱的氧化鋅結異質接面結構，因具有較大的表面積／體積比，即使在完全相同的成長條件下，其飽和磁化強度比直接成長在矽平面基板的氧化鋅薄膜，可以大上兩個數量級。此一結果，應可對於方興未艾的自旋電子學，提供一定程度的參考價值。

This thesis aims to investigate the electrical transport properties and room-temperature ferromagnetism of ultrathin ZnO films grown by atomic layer deposition (ALD) method. For the electrical transport part, we had made systematic studies on how growth temperature affects the microstructure, transport and optoelectronic properties of a series of Al-doped ZnO (AZO) films with thickness of 20-30 nm deposited on polished silicon-(100) and glass substrates by the atomic layer deposition (ALD). Specifically, effective Al-doping was achieved by an in-situ doping-growth scheme with the growth temperature ranging from 100 ℃ to 300 ℃. Experimental results showed that, in general, increasing the growth temperature would result in much improved film crystallinity and carrier mobility, with the average transmittance in the visible wavelength range being exceeding 95 % in all cases. In particular, for AZO films grown at 300 ℃, an unprecedented mobility of 136 cm^2 V^(-1) s^(-1), comparing to the typical values of 50~60 cm^2 V^(-1) s^(-1) reported previously, was obtained. Despite that the resistivity (ρ≈6×〖10〗^(-4) Ω-cm) of the 300 °C AZO films is still slightly higher than that of some highly-doped ZnO (ρ=2~4×〖10〗^(-4) Ω-cm) prepared by sputtering method. The secondary ion mass spectroscopy (SIMS) analyses revealed that hydrogen incorporation is the key in reducing the charge trap density and, hence, resulting in much enhanced carrier mobility. The present results promise a keen competitiveness of AZO with the indium tin oxide (ITO) film for thin-film-transistor (TFT) as well as in photovoltaic device applications.
On the other hand, the origin that gives rise to room-temperature ferromagnetism (RTFM) in various pristine oxide semiconductors, including ZnO, has been, and still is, a subject of extensive debates. In the second part of this thesis, we made detailed comparisons of RTFM exhibited in a series of un-doped ZnO thin films using ALD. The films were deliberately deposited on Si-substrate and substrates with Si-nanopillars (Si-NP) at different deposition temperatures. Photoluminescence (PL) and X-ray photoelectron spectroscopies (XPS) demonstrate clearly that at lower deposit temperatures of ZnO films grown on both types of substrates are having larger concentration of defects, which, in turn, resulting in more pronounced RTFM. Specifically, for films grown on Si-NPs, a remarkable saturation magnetization (M_s=1.76 emu/cm^3) with a Curie temperature (T_C=404K) is observed. Further analyses indicate that the RTFM arises primarily from the interaction between singly charged oxygen vacancy (V_O^+) and Zinc vacancy (V_Zn), which is consistent with the defect-mediated bound magnetic polaron model. Moreover, due to the large surface/volume ratio, the silicon-NP/ZnO core/shell heterostructure evidently exhibited nearly two order of magnitude improvement in the magnitude of saturation magnetization with slightly higher Curie temperature. The present results may have significant implications in the spintronics applications.

摘要 I
Abstract III
Acknowledgements V
Contents VI
Table captions VIII
Figure captions IX
1. Introduction 1
1-1 Background 1
1-2 Synopsis of Chapters 1
2. Semiconductor Physics 3
2-1 Zinc Oxide 3
2-2 Electrical properties 6
2-2-1 Hall-Effect [19] 6
2-2-2 The literature for electric property of ZnO-based material 8
2-3 Magnetic properties 10
2-3-1 Curie temperatures (Tc) 10
2-3-2 Hund’s rule 10
2-3-3 Diluted Magnetic Semiconductors (DMSs) 11
2-3-4 Exchange interaction [32] 12
2-3-5 The literature for magnetic property of ZnO-based material 14
2-4 Atomic Layer Deposition 17
2-5 Motivation 20
3. Experimental techniques 21
3-1 Experimental flow chart 21
3-2 Atomic layer deposition (ALD) 22
3-3 Inductively coupled plasma chemical vapor deposition (ICPCVD) 22
3-4 X-ray diffraction (XRD) 23
3-5 Transmission electron microscope (TEM) 24
3-6 Secondary ion mass spectrometry (SIMS) 24
3-7 Photoluminescence (PL) 25
3-8 Ultraviolet–visible spectroscopy (UV-Vis) 25
3-9 Hall-Effect measurement 26
3-10 X-ray photoemission spectroscopy (XPS) 26
3-11 Superconducting Quantum Interference Device (SQUID) 27
4. High mobility transparent conductive AZO thin films by ALD 28
4-1 Structure property 28
4-2 Optical and electric property 31
5. Enhancement of ferromagnetic from ultrathin ZnO films grown on Si-nanopillars by atomic layer deposition 38
5-1 Structure Property 38
5-2 Optical and magnetic property 40
6. Conclusion 46
Reference 48

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