臺灣博碩士論文加值系統

本論文中，我們首先探討兩種不同的金屬作為歐姆接觸時對氮化鋁鎵/氮化鎵異質結構場效電晶體之結構特性的影響。當以鉻/鋁為歐姆接觸電極時，在700℃氮氣退火的環境下有最佳的特徵電阻值3.7*10-4Ω-cm2，此時元件在直流特性方面最高轉導(GM)為82.4mS/mm、最大電流(Idmax)為471mA/mm。而以鈦/鋁/鈦/金為歐姆接觸電極時，在800℃氮氣退火的環境下有最佳的特徵電阻值2*10-5Ω-cm2，元件在直流特性方面最高轉導(GM)為100.9mS/mm、最大電流(Idmax)為481mA/mm。由以上可知，當我們選擇有較低的特徵電阻值的金屬做電極時，對元件特性的確有很大的影響。在高頻部分我們以HP8150網路分析儀量得以鈦/鋁/鈦/金為歐姆接觸電極所做出的元件之截止頻率為1.32GHz及1.99GHz的最大共振頻率。
另外，我們在有機金屬氣相磊晶法成長的氮化鎵基板上利用分子束磊晶法(MBE)成長出高品質的二維電子雲，其成長出的試片在室溫時的濃度及電子遷移率分別為1.77E+13cm-2和1010cm2/V-sec，此試片我們也做出元件並和完全以有機金屬氣相磊晶法成長之試片所做出的元件做比較。
在第二部分我們探討由能帶彎曲及壓電效應所形成之氮化鎵/氮化銦鎵異質結構場效電晶體之元件特性，我們發現在摻雜鎂之氮化鎵絕緣層上成長一層薄的氮化鎵緩充層及減少氮化銦鎵厚度至(1000Å)可有效的提升氮化鎵/氮化銦鎵介面的二維電子雲品質，由原子力顯微鏡量測得到0.23nm的表面粗糙度，以及376cm2/V-sec、1.2E+13cm-2的二維電子雲遷移率和濃度即是最好的證明，此外，我們也由元件的特性發現，摻雜鎂之氮化鎵絕緣層的確可有效的降低源極端和汲極端之間的漏電流，但在低頻雜訊的表現上，因為摻雜鎂之氮化鎵絕緣層會對結構形成較多的缺陷，因此對通道內的電流傳輸及電子的遷移率會有較大的影響，也就有較大的雜訊產生。

In this thesis, we first compare two different type ohmic contact metals on AlGaN/GaN heterostructure field effect transistors (HFETs) structure grown by metalorganic vapor phase epitaxy (MOVPE) system, and then discuss the device electrical characteristics .With Cr/Al for ohmic contact metals, the best specific contact resistivity we measured is 3.7*10-4Ω-cm2 annealed at 700℃ in N2 ambiance. In DC section, the maximal transconductance (GM) of device is 82.4mS/mm and the maximal drain current (Idmax) is 471mA/mm. For using Ti/Al/Ti/Au as ohmic contact metals, the best specific contact resistivity is 2*10-5Ω-cm2 annealed at 800℃in N2 ambiance. For DC measurement, the maximal transconductance and the maximal drain current (Idmax) are 100.9mS/mm and 481mA/mm. So, we know lower specific contact resistivity indeed has improvement on the device electrical characteristics. Beside, from measuring the HFETs structure with Ti/Al/Ti/Au as ohmic contact metals, we obtain the cut-off frequency fT=1.32GHz and maximum oscillation frequency fmax= 1.99 GHz by HP8150 network analyzer.
We also get high 2DEG layers quality by using Ammonia-MBE system grown on MOVPE GaN template; the 2DEG sheet carrier density and hall nobility are 1.77E+13cm-2 and 1010cm2/V-sec at room temperature. We also compare devices electrical characteristics with devices grown totally on MOVPE system.
In the second section, we study and fabrication of GaN/InGaN heterostructure field effect transistors caused by bend bending and piezoelectric effect. We find that grow a thin GaN buffer layer on GaN:Mg isolation layer and reduce InGaN layer thickness to 1000 Å can improve the GaN/InGaN 2DEG quality. The best evidences are 0.23nm surface roughness obtained from AFM technique and 376cm2/V-sec、1.2E+13cm-2 of hall mobility and sheet carrier density. Moreover, we also find that GaN:Mg isolation layer can lower leakage current from drain to source, but it provides more traps and defects in the structure and causes pronounced electrons and mobility fluctuation at channel layer, so higher noise power spectral density than structure without GaN:Mg isolation layer can be measured by Flicker noise measurement system.

Contents
Abstract (in Chinese) I
Abstract (in English) III
Contents V
Table Captions VIII
Figure Captions IX

Chapter 1 Introduction
1-1 The background research on GaN and AlGaN/GaN
heterostructure 1
1-2 The background research on GaN/InGaN
heterostructure 2
1-3 Overview of This Dissertation 3
References 7

Chapter 2 Theory and Measurement Techniques
2-1 X-Ray Diffraction (XRD) System 9
2-2 SIMS (Secondary Ion Mass Spectroscopy) 10
2-3 Inductively coupled plasma reactive ion
etching (ICP-RIE) 10
2-4 The investigation of 2-DEG measurement 12
2-5 Network analyzer system 15
2-6 Noise model of flicker noise 15
References 23


Chapter 3 Discussion the ohmic contact behavior
on AlGaN/GaN HFETs structure
3-1 Introduction 24
3-2 Theory of the circular transfer length
method (CTLM) measurement 25

3-3 Growth Conditions and Characteristics of
AlGaN/GaN HFETs Structures by MOVPE
system 27
3-4 Fabrication processes 28
3-5 Result and discussion 29
3-6 Summary 32
References 41

Chapter 4 Study of the fabrication and
characteristics of AlGaN/GaN HFETs
grown by MOVPE system
4-1 Introduction 43
4-2 polarization 44
4-3 AlGaN/GaN HFETs devices fabrication processes 47
4-4 Discussion of devices electrical
characteristics by using different type
ohmic contact metals 49
4-5 AlGaN/GaN 2DEG structure grown by ammonia-MBE
on MOVPE GaN template 52
4-6 Low frequency noise on AlGaN/GaN 2DEG
structure grown by ammonia-MBE techniques
on MOVPE GaN template and totally grown
by MOVPE system 55
References 73

Chapter 5 Study of the fabrication and
characteristics of GaN/InGaN
HFETs grown by MOVPE system
5-1 Introduction 75
5-2 Growth Conditions and Characteristics of
GaN/InGaN HEMTs Structures by MOVPE system 75
5-3 Result and discussion 76
5-4 Study of GaN/In0.12Ga0.88N HFETs with Mg-doped
GaN confinement layer 77
References 89

Chapter 6 Conclusion and future prospect
6-1 Conclusion 90
6-2 future prospect 91

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