臺灣博碩士論文加值系統

氮化鋁鎵/氮化鎵摻雜通道場效電晶體之研究

王富民* 蔡榮輝**

國立高雄師範大學電子工程學系碩士班

摘要

本論文中主要建造並探討氮化鋁鎵/氮化鎵高電子遷移率電晶體之通道摻雜的影響，以及摻雜厚度對於氮化鋁鎵/氮化鎵摻雜通道高電子遷移率電晶體特性之影響。探討及分析的結構分別為:
(1)氮化鋁鎵/氮化鎵在具有200埃氮化鎵摻雜通道之高電子遷移率電晶體(元件A)。
(2)氮化鋁鎵/氮化鎵無摻雜通道之高電子遷移率電晶體(元件B)。
(3)氮化鎵摻通道區域分別為195、190、175、150、100、50埃且距離氮化鋁鎵/氮化鎵異質接面之間隙層分別為5、10、25、50、100、150埃之高電子遷移率電晶體(元件C、D、E、F、G、H)。
元件A的製作是使用有機金屬化學氣相沉積系統將結構層成長於藍寶石基板上。實驗的結果顯示集極飽和電流和轉導值分別為506.9 mA/mm和52.475 mS/mm。另外，將實驗數據與模擬數據直流特性相互匹配，在模擬上使用適當的參數讓模擬數據接近實驗結果，提高模擬準確度。
模擬結果顯示，由於通道有摻雜(元件A)其二維電子雲氣(2DEG)的載子濃度將較無摻雜通道元件(元件B)來得高。由於通道摻雜後2DEG內的雜質濃度上升，使得雜質散射效應影響上升，2DEG內的載子移動率進而下降，故其通道摻雜使得汲極飽和電流、轉導值、臨界電壓、崩潰電壓與高頻特性受到影響而特性變差。而元件C、D、E、F、G、H將摻雜層遠離2DEG通道，可減少雜質散射效應。研究結果顯示，通道摻雜元件(元件F、G、H)其元件特性是優於無摻雜通道元件(元件B)。元件F、G、H獲得比元件B還要高的2DEG，其濃度分別為1.158 × 1020、1.155 × 1020、1.154 × 1020 cm-3，最大飽和電流與最大轉導值分別為672、682、689.7 mA/mm與84.4、87、89.4 mS/mm，單位電流增益截止頻率與最大震盪頻率分別為17.8、18.1、18.3 GHz與28.3、29.1、29.2 GHz。

* 研究生
** 指導教授

關鍵字 : 氮化鋁鎵/氮化鎵、高電子遷移率電晶體、摻雜通道、雜質散射

Investigation of AlGaN/GaN Doping-Channel High Electron Mobility Transistors

Fu-Min Wang* Jung-Hui Tsai**

Department of Electronics, National Kaohsiung Normal University, Kaohsiung, Taiwan, R.O.C

Abstract

In this dissertation, we will fabricate and investigate the impact of doping channel on the AlGaN/GaN doping-channel high electron mobility transistors, and the influence of doped thickness on AlGaN/GaN doping-channel high electron mobility transistors will be included. The structures were designed as follows:
(1) AlGaN/GaN doping-channel high electron mobility transistor with channel doping region thickness of 20 nm (called Device A).
(2) AlGaN/GaN high electron mobility transistor without GaN doping-channel layer (called Device B).
(3) AlGaN/GaN doping-channel high electron mobility transistor with a channel doping region thickness of 19.5, 19, 17.5, 15, 10, and 5 nm, respectively, and with a spacer close to the AlGaN/GaN heterojunction of 0.5, 1, 2.5, 5, 10, and 15 nm, respectively (called Devices C, D, E, F, G, and H).
The device (Device A) was fabricated by metal-organic chemical vapor deposition system on a sapphire substrate. The experimental results exhibit a maximum drain saturation current of 506.9 mA/mm and a maximum transconductance of 52.475 mS/mm. Also, we will simulate the DC performance of device A with doping channel according to the experimental data. The simulated characteristics are close to the experimental results by choosing the proper parameters.
Simulation results show that the 2DEG concentration of the device A is higher than the device B without the doping-channel layer. The doping channel will enable the 2DEG concentration to increase. However, the impurity scattering of carriers in the doping channel will lead to the electron mobility to decrease. The results show that the device A with a doping channel has poor output saturation current, transconductance, gate leakage current, breakdown voltage, and high-frequency characteristics. In addition, the doping layer of devices C, D, E, F, G, and H are away from the 2DEG. It can decrease the effect of impurity scattering. The result exhibits that the DC and high-frequency characteristics of the devices F, G, and H are better than the device B. In the devices F, G, and H, the 2DEG carrier concentrations are 1.158 × 1020, 1.155 × 1020, and 1.154 × 1020 cm-3, the maximum output currents are of 672, 682, and 689.7 mA/mm, and transconductance are 84.4, 87, and 89.4 mS/mm, respectively. Furthermore, the unity gain cut-off frequencies are 17.8, 18.1, and 18.3 GHz, and maximum oscillation frequencies are 28.3, 29.1, and 29.2 GHz respectively.

* Author
** Advisor
KEYWORDS : AlGaN/GaN, high electron mobility transistor, doping channel, impurity scattering

CONTENTS
Abstract (Chinese) I
Abstract (English) IV
Table Lists XVII
Figure Captions XVIII
Chapter 1 Introduction 1
1.1 General Background Information 1
1-2 Properties of Materials 1
1-3 High Electron Mobility Transistors (HEMTs) 2
1-4 Purpose of Research 4
1-5 Thesis Organizations 4
Chapter 2 The impact of doping channel on AlGaN/GaN doping-channel high electron mobility transistors (HEMTs) 6
2-1 Introduction 6
2-2 Device Fabrication and Simulation Environment 7
2-2-1 Device Fabrication 7
2-2-2 Device Model of Simulation 7
2-3 Device Structures 8
2-4 Result and Discussion 8
2-5 Conclusion 14
Chapter 3 The influence of doped thickness on AlGaN/GaN doping-channel high electron mobility transistors (HEMTs) 16
3-1 Introduction 16
3-2 Device Structure 17
3-3 Result and Discussion 18
3-3-1 DC and RF Characteristics 18
3-3-2 Comparison of Devices B and H 21
3-4 Conclusion 22
Chapter 4 Conclusion and Prospect 23
4-1 Conclusion 23
4-2 Prospects and Future Work 24
References 27
Tables 33
Figures 36

Table Lists

Table I Summary of physical models.
Table II Simulated results of the devices C, D, E, F, G and H.
Table III Simulated results of the devices B and H.


Figure captions

Figure 2-1 Schematic diagram of the cross section and top view of the studied AlGaN/GaN doping-channel HEMT.
Figure 2-2 Schematic cross section of device B with simulated structure.
Figure 2-3 Comparison of simulated (solid line) and experimental (dashed line) drain-to-source saturation current and transconductance versus the gate bias.
Figure 2-4 Comparison of simulated (solid line) and experimental (dashed line) I-V characteristics. The controlled gate voltage is applied by -1 V/step.
Figure 2-5 (a) Corresponding energy-band diagram from the middle of gate to buffer layer of the device A at equilibrium.
(b) Corresponding energy-band diagram from the middle of gate to buffer layer of the device B at equilibrium.
(c) Comparison of conduction bands near the AlGaN/GaN heterojunction of devices A and B at equilibrium.
Figure 2-6 Comparison of electron concentrations of devices A and B at equilibrium.
Figure 2-7 Relation between drain current and gate-to-source voltage of the devices A and B.
Figure 2-8 (a) Simulated I-V characteristics of the device A. The controlled gate voltage is applied by -1 V/step.
(b) Simulated I-V characteristics of the device B. The controlled gate voltage is applied by -1 V/step.
Figure 2-9 (a) Comparison of electron velocities of devices A and B at VGS = 0 V.
(b) Comparison of electron velocities of devices A and B at VGS = 3 V
Figure 2-10 (a) Drain-to-source saturation current and transconductance versus gate bias of device A.
(b) Drain-to-source saturation current and transconductance versus gate bias of device B.
Figure 2-11 The inverted gate-to-drain current-voltage characteristics of the devices A and B.
Figure 2-12 (a) Microwave performance of the device A.
(b) Microwave performance of the device B.
Figure 3-1 (a) Schematic cross section of device C with simulated structure.
(b) Schematic cross section of device D with simulated structure.
(c) Schematic cross section of device E with simulated structure.
(d) Schematic cross section of device F with simulated structure.
(e) Schematic cross section of device G with simulated structure.
(f) Schematic cross section of device H with simulated structure.
Figure 3-2 Comparison of conduction bands near the AlGaN/GaN heterojunctions of devices C, D, E, F, G and H.
Figure 3-3 Comparison of electron concentrations of devices C, D, E, F, G and H
Figure 3-4 (a) Simulated I-V characteristics of the device C. The controlled gate voltage is applied by -1 V/step.
(b) Simulated I-V characteristics of the device D. The controlled gate voltage is applied by -1 V/step.
(c) Simulated I-V characteristics of the device E. The controlled gate voltage is applied by -1 V/step.
(d) Simulated I-V characteristics of the device F. The controlled gate voltage is applied by -1 V/step.
(e) Simulated I-V characteristics of the device G. The controlled gate voltage is applied by -1 V/step.
(f) Simulated I-V characteristics of the device H. The controlled gate voltage is applied by -1 V/step.
Figure 3-5 (a) Comparison of electron velocities of devices C, D, E, F, G, and H at VGS = 0 V.
(b) Comparison of electron velocities of devices C, D, E, F, G, and H at VGS = 3 V.
Figure 3-6 Relation between drain current and gate-to-source voltage of the devices C, D, E, F, G and H
Figure 3-7 (a) Drain-to-source saturation current and transconductance versus gate bias of device C.
(b) Drain-to-source saturation current and transconductance versus gate bias of device D.
(c) Drain-to-source saturation current and transconductance versus gate bias of device E.
(d) Drain-to-source saturation current and transconductance versus gate bias of device F.
(e) Drain-to-source saturation current and transconductance versus gate bias of device G.
(f) Drain-to-source saturation current and transconductance versus gate bias of device H.
Figure 3-8 The inverted gate-to-drain current-voltage characteristics of the devices C, D, E, F, G and H.
Figure 3-9 (a) Microwave performance of the device C.
(b) Microwave performance of the device D.
(c) Microwave performance of the device E.
(d) Microwave performance of the device F.
(e) Microwave performance of the device G.
(f) Microwave performance of the device H.

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