臺灣博碩士論文加值系統

中文摘要

　　本篇論文中，是研究摻雜鋯(Zirconium，Zr)金屬於氧化鋅(Zinc-Oxide，ZnO)薄膜的材料特性分析及實際應用的研究，鋯金屬分別以重量百分比8.2wt%、10wt%、15wt%不同濃度摻雜於氧化鋅中，藉以瞭解摻雜鋯金屬後的氧化鋅(Zr-doped ZnO，ZZO)透明導電膜的特性；並以此薄膜當作P型氮化鎵(p-GaN)傳輸線元件的電極，研究透明導電膜與半導體間之接觸特性。

　　首先，以射頻（Radio Frequency，RF）共濺鍍(Co-sputtering)系統將氧化鋅材料與鋯金屬同時濺鍍於藍寶石(Al2O3)基板上，形成ZZO透明導電薄膜，再經由適當的熱處理，並且針對不同的熱處理狀況研究薄膜的光學與電學特性。在最佳濺鍍條件下，作出傳輸線模型元件後，通入不同氣體來做熱處理，研究不同的熱處理條件對於接觸特性的影響。

　　在實驗結果方面，以濺鍍機反應室氣壓10mtorr，入射功率：
氧化鋅靶材為300Watt、金屬鋯靶材為30Watt，通入氬氣(Ar)15sccm，以鋯金屬重量百分比8.2wt%的濃度摻雜於氧化鋅中的ZZO透明導電膜有較佳之光特性與電特性。在經過1100oC的高純度氮氣熱處理1分鐘後，電阻率ρ為3.02×10-3Ω-cm，載子濃度為-8.32×1020cm-3；薄膜穿透率在可見光波段平均可達到85%以上的水準，而摻雜鋯金屬試圖提高薄膜的載子濃度，以期在穿透率可以符合柏斯坦-摩斯(Burstein-Moss)效應並且有藍移現象，而在此最佳製程參數下：ZZO透明導電薄膜在380nm波長之穿透率從原本為10.7%提高至86.6%。

　　以此條件製作出的傳輸線(Transmittance line model，TLM)元件的電極後，在高純度氮氣環境下，以900OC熱處理1分鐘之熱處理條件有較低的特徵電阻值，在P型氮化鎵的試片量測到歐姆接觸的特性，特徵電阻值ρC 為3.80×10-4Ω-cm2。

Abstract

　In this thesis, the materials characteristics of zirconium (Zr) doped zinc oxide (ZnO) films and their contacts on p-type GaN were investigated. The transparent and conductive ZnO films were doped with Zr atoms at concentrations of 8.2, 10 and 15 wt%, respectively. Sequentially, the contact properties of the optimum transparent and conductive ZZO films contacted on p-type GaN were conducted from a transmittance line model (TLM).
These ZnO films doped at various Zr atoms were deposited on sapphire (0001) substrates using a cosputtering system employed ZnO and Zr targets. Post-annealing treatments were also carried out to improve the associated optical properties in ultraviolet region and electrical characteristics of these ZZO films. A ZZO film possessed superior optical and electrical properties was achieved at a doped concentration of Zr atoms reaching 8.2 wt%. After annealing at 1100 oC for 1 min. under nitrogen ambience, the resistivity and carrier concentration of this ZZO films were improved to 2.21 × 10-3 Ω cm and 3.26 × 1020 cm-3, respectively. Meanwhile, a superior average transmittance higher than 85 % in visible region was also obtained. Furthermore, the absorption edge of this annealed ZZO films (Zr: 8.2 wt%) was found to blue-shift attributed to Burstein-Moss effect. the transmittance at 380 nm in ultraviolet region was therefore enhanced from 10.7 % (without post-annealing treatment) to 86.6 %.

　As a result of producing dissolution of GaN for annealing above high temperature (>900oC), the better annealing condition for transmittance line model devices is annealing treatment at 900oC for 1 minute in pure N2. The electrodes of TLM devices which were made under above conditions would have lower specific resistances. We measured the characteristic of ohmic contact from the sample of p-GaN, the specific contact resistances ρC = 3.80×10-4Ω-cm2.

Contents

中文摘要 / I
Abstract / III
Contents / V
List of Tables/ VII
List of Figures / VIII

Chapter 1 Introduction / 1
Chapter 2 Background Theory / 5
2.1 The crystal structure and characteristics of ZnO / 5
2.2 Theory of sputtering / 6
2.3 Theory of Metal-Semiconductor Contact / 8
2.4 Current Transport Mechanism / 10
2.5 Measurement of Contact Resistance / 10
Chapter 3 Optical and electrical properties of ZZO films grown by RF co-sputter / 13
3.1 The Procedures of ZZO films / 13
3.1.1 Clean samples / 13
3.1.2 Sputtering procedures / 14
3.2 Annealing procedures / 16
3.3 Analysis of measurement / 19
3.3.1 Thickness measurement / 19
3.3.2 Hall measurement / 19
3.3.3 Transmittance measurement / 22
3.3.4 Photoluminescence (PL) measurement / 25
3.3.5 Absorption coefficient and energy band gap / 25
3.3.6 XRD and SEM measurement / 26
3.4 Results and discussion / 27
Chapter 4 Investigation of p type GaN ohmic contact with ZZO / 29
4.1 The procedures of thin metal contact with p type GaN / 29
4.1.1 Split and active samples / 29
4.1.2 Clean samples / 30
4.1.3 Photolithography / 31
4.1.4 Metal deposition and lift off of pattern / 31
4.1.5 The process of mesa etching of transmittance line model / 32
4.1.6 The process of removing original oxides / 32
4.1.7 Evaporate electrode / 32
4.1.8 Annealing treatment / 33
4.2 The procedures of depositing ZZO films on p-GaN/ Ni, Au (oxided) / 33
4.3 Results and discussion / 34
Chapter 5 Conclusion / 37
Reference / 39

List of Tables
Table.1 Results from conductivity and optical measurements of ZZO (Zr: 15wt%) films/ 42
Table.2 Results from conductivity and optical measurements of ZZO (Zr: 10wt%) films/ 42
Table.3 Results from conductivity and optical measurements of ZZO (Zr: 8.2wt%) films/ 42

List of Figures
Fig. 2.1 A hexagonal wurzite structure of ZnO
(small and large circles are zinc and oxygen atoms, respectively) / 43
Fig. 2.2 A diagram of RF sputtering system / 44
Fig. 2.3 Metal - Semiconductor contacts before and after / 45
Fig. 2.4 Energy band related diagram under various metal work function differences / 45
Fig. 2.5 Current transport mechanisms under different doping concentrations / 46
Fig. 2.6 A schematic configuration to extract sheet resistance, contact resistance / 47
Fig. 3.1 Configuration of RF cosputtering system / 48
Fig. 3.2 Deposition rate of ZnO films as functions of RF power / 49
Fig. 3.3 Deposition rate of Zr films as functions of RF power /50
Fig. 3.4 Deposition rate of Zr films as functions of distances between substrate and target Zr at RF power of 30W /51
Fig. 3.5 Resistivity, carrier concentration and hall mobility of ZZO (Zr: 15wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 52
Fig. 3.6 Resistivity, carrier concentration and hall mobility of ZZO (Zr: 15wt%) films for various annealing times under N2 atmosphere at 700oC / 53
Fig. 3.7 Transmittance of ZZO (Zr: 15wt%) films at various annealing temperatures under N2 atmosphere for 1 minute /54
Fig. 3.8 Transmittance of ZZO (Zr: 15wt%) films for various annealing times under N2 atmosphere at 700oC / 55
Fig. 3.9 Transmittance of ZZO (Zr: 15wt%) films for various annealing times under N2 atmosphere at 1100oC / 56
Fig. 3.10 Resistivity, carrier concentration and hall mobility of ZZO (Zr: 8.2wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 57
Fig. 3.11 Resistivity, carrier concentration and hall mobility of ZZO (Zr: 10wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 58
Fig. 3.12 Resistivity, carrier concentration and hall mobility of ZZO (Zr: variable) films under N2 atmosphere at 900oC for 1 minute / 59
Fig. 3.13 Resistivity, carrier concentration and hall mobility of ZZO (Zr: variable) films under N2 atmosphere at 1100oC for 1 minute / 60
Fig. 3.14 Transmittance of ZZO (Zr: 8.2wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 61
Fig. 3.15 Transmittance of ZZO (Zr: 10wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 62
Fig. 3.16 Transmittance of ZZO (Zr: 15wt%) films at various annealing temperatures under O2 atmosphere for 1 minute / 63
Fig. 3.17 Resistivity, carrier concentration and hall mobility of ZZO (Zr: 10wt%) films at various annealing temperatures under H2 atmosphere for 1 minute / 64
Fig. 3.18 Transmittance of ZZO (Zr: 10wt%) films at various annealing temperatures under H2 atmosphere for 1 minute / 65
Fig. 3.19 PL spectrum diagram of ZZO (Zr: 15wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 66
Fig. 3.20 PL spectrum diagram of ZZO (Zr: 15wt%) films at various annealing temperatures under O2 atmosphere for 1 minute / 67
Fig. 3.21 A absorption coefficient of ZZO (Zr: 10wt%) films at various annealing temperature under N2 atmosphere for 1 minute / 68
Fig. 3.22 A absorption coefficient of ZZO (Zr: 15wt%) films at various annealing temperature under N2 atmosphere for 1 minute / 69
Fig. 3.23 Energy bandgap extracted from absorption edge of as-deposited ZnO and annealed ZZO films / 70
Fig. 3.24 XRD diagram of ZZO (Zr: 10wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 71
Fig. 3.25 XRD diagram of ZZO (Zr: 15wt%) films at various annealing temperatures under N2 atmosphere for 1 minute / 72
Fig. 3.26 The scanning electron micrograph of ZnO films doped with (a) 8.2,(b) 10 and (c) 15 wt% / 73
Fig. 4.1 A schematic process for TLM devices (I)/ 74
Fig. 4.2 A schematic process for TLM devices (II) / 75
Fig. 4.3 A schematic process for TLM devices (III) / 76
Fig. 4.4 Plane-view of (a) mesa in TLM and (b) p-GaN/ Ni, Au (oxided)/ Ti/ ZZO device / 77
Fig. 4.5 the I-V characteristics of p-GaN/ ZZO at various annealing temperature under N2 atmosphere for 1 minute / 78
Fig. 4.6 the I-V characteristics of p-GaN/ Ni/ Au at 500oC under air atmosphere for 3 minute / 79
Fig. 4.7 the I-V characteristics of p-GaN// Ni, Au (oxided)/ ZZO at various annealing temperature under N2 atmosphere for 1 minute / 80
Fig. 4.8 the I-V curve of p-GaN/ Ni, Au (oxided)/ Ti/ ZZO at different annealing temperature under pure N2 gas for 1 minute / 81
Fig. 4.9 the I-V curve of p-GaN/ Ni, Au (oxided)/ Ti/ ZZO on various Ti thickness at 900oC under N2 atmosphere for 1 minute/ 82
Fig. 4.10 Contact resistance as function of different effective spacing of p-GaN/ Ni, Au (oxided)/ Ti/ ZZO at various annealing temperatures under N2 atmosphere for 1 minute / 83

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