臺灣博碩士論文加值系統

本論文研係研製以「金屬有機化學氣相沉積」方式成長具有雙載子提供層之 砷化鋁鎵/砷化銦鎵/砷化鎵通道摻雜式異質結構場效體，並藉由V型通道結構與雙重δ-摻雜載子提供層等設計以改善載子侷限能力、電子傳輸特性、元件增益、電流驅動能力與閘極偏壓擺幅等元件特性。

相較於傳統之調變式摻雜異質結構場效體結構，通道摻雜式場效體擁有較佳載子侷限能力與元件增益線性度之優點；而在δ-摻雜之擬晶式高電子遷移率電晶體，由於使用未摻雜的通道結構設計來消除通道中的雜質散射效應，所以將有較高的外部轉導增益值。因此，本論文在結合通道摻雜式異質結構場效體之高增益線性度之優點，藉由雙重δ-摻雜載子提供層的設計來提升載子濃度、增加電流密度之特性表現。尤其，藉由對稱漸變的摻雜式通道結構設計，透過改變砷化銦鎵通道中的銦成分之線性漸變方式(0.15à 0.2à0.15)，因而獲致一V型的傳導帶分布，使電子遠離砷化鋁鎵/砷化銦鎵界面，降低庫侖散射效應，將有效改善閘極偏壓擺幅與電子傳輸能力等特性；另本論文在閘極金屬與主動通道層間插入一寬能隙未摻雜層之設計以改善元件崩潰特性。

實驗結果顯示，相較於傳統通道摻雜式場效體，此元件設計擁有較高的載子遷移率、較高的外部轉導值及較高的截止頻率；而相較於δ-摻雜高電子遷移率電晶體，此設計亦擁有較好的線性度、較大的閘極偏壓擺幅及較大的輸出功率。最後，本論文亦探討該砷化鋁鎵/砷化銦鎵/砷化鎵異質結構場效體之溫度變化特性與高頻等特性比較。

In this thesis, we intend to grown the double δ-doped Al0.3Ga0.7As/InxGa1-xAs/GaAs Doped-Channel heterostructure field-effect transistor by low-pressure metal organic chemical vapor deposition (LP-MOCVD) has been studied. The V-shape InGaAs channel and dual δ-doping carrier supply layers design were expected to improve carrier confinement, electron transport properties, gain, current drive capability and gate voltage swing,

By using the doped-channel scheme instead of the modulation-doped one, in DCFET’s could attain a better carrier confinement and device linearity. However, the conversional pseudomorphic HEMTs exhibiting higher extrinsic transconductance, due to the impurity scattering effect will be eliminated in undoped InGaAs channel. In this work, we composite the high-gain and high-linearity of doped-channel HFETs, and use the dual δ-doping carrier supply layers to enhance the carrier concentrations and current density. Especially, we use the symmetric graded channel structure by changing the In composition (0.15à 0.2à0.15). The electron will be confined well in the bottom of V-shape conduction band. Thus, the electrons are less closer to the AlGaAs/InGaAs interface, and Coulomb scattering lower down. Meanwhile, we can improve the electron transport property and gate voltage swing (GVS). In addition, the insertion of undoped wide bandgap layer between the metal gate and action channel can in deed improve the characteristics of breakdown voltage and turn-on voltage.

The experimental results which compare with conversional DCFETs show higher carrier mobility, extrinsic transconductance, and cut-off frequency. As compared with the pseudomorphic HEMTs, the linearity, GVS and output power will be improved.The temperature-dependent characteristics of AlGaAs/InGaAs/GaAs heterostructure field-effect transistors have also been studied.

Acknowledgement……………i
Abstract (Chinese)……………ii
Abstract (English)……………iii
Figure Captions……………vii
Chapter 1 Introduction……………1
Chapter 2 Epitaxial Growth System and Experimental Procedures……………4
2-1 Introduction of LP-MOCVD System……………4
2-2 Device fabrication Processes……………7
2-2-1 Sample Orienting……………7
2-2-2 Mesa Isolation……………7
2-2-3 Source and Drain Ohmic Contact Formation……………8
2-2-4 Gate Schottky Contact Formation……………9
Chapter 3 Device Structures of AlGaAs/InGaAs/GaAs HFETs……………10
3-1 Device Structures……………10
3-2 Hall Measurement……………11
Chapter 4 Experimental Results and Discussions……………14
4-1 DC Characteristics at 300K……………14
4-1-1 Current-Voltage Characteristics……………14
4-1-2 Extrinsic Transconductance Characteristics……………15
4-1-3 Two-terminal Breakdown Voltage Characteristics……………17
4-1-4 Output Conductance……………18
4-2 RF Characteristics……………18
4-3 Power Characteristics……………20
4-4 Noise Characteristics……………21
4-5 Temperature-dependent characteristics……………22
4-5-1 Extrinsic Transconductance Characteristics……………22
4-5-2 Two-terminal Breakdown Voltage Characteristics……………24
4-5-3 RF Characteristics……………24
Chapter 5 Conclusions……………26
Reference……………27
Fig. 2-1 A schematic diagram of LP-MOCVD……………32
Fig. 2-2 A schematic of the our experiment procedure……………33
Fig. 3-1 The cross section of the sample A……………34
Fig. 3-2 The cross section of the sample B……………35
Fig. 3-3 The cross section of the sample C……………36
Fig. 4-1 Current-Voltage characteristics of sample A at 300K……………37
Fig. 4-2 Current-Voltage characteristics of sample B at 300K……………38
Fig. 4-3 Current-Voltage characteristics of sample C at 300K……………39
Fig. 4-4 Extrinsic transconductance and saturation drain current density of sample A of VDS=3V at 300K……………40
Fig. 4-5 Extrinsic transconductance and saturation drain current density of sample B of VDS=3V at 300K……………41
Fig. 4-6 Extrinsic transconductance and saturation drain current density of sample C of VDS=3V at 300K……………42
Fig. 4-7 Extrinsic transconductance as a function of the drain current density of our studied AlGsAs/InGaAs/GaAs HFETs……………43
Fig. 4-8 Two- terminal Breakdown voltage (a) and turn-on voltage (b) characteristics of our studied devices at 300K……………44
Fig. 4-9 The extrinsic transconductance, output conductance and voltage gain characteristics versus drain voltage for sample A……………45
Fig. 4-10 The extrinsic transconductance, output conductance and voltage gain characteristics versus drain voltage for sample B……………46
Fig. 4-11 The extrinsic transconductance, output conductance and voltage gain characteristics versus drain voltage for sample C……………47
Fig. 4-12 RF characteristics of sample A at VDS= 3V, VGS= 0V for gate dimension = 1.2×200 μm2……………48
Fig. 4-13 RF characteristics of sample B at VDS= 3V, VGS= -0.5V for gate dimension = 1.2×200 μm2……………49
Fig. 4-14 RF characteristics of sample C at VDS= 3V, VGS= -0.5V for gate dimension = 1.2×200 μm2……………50
Fig. 4-15 The output power, power gain and power added efficiency (PAE) characteristics versus input power at 2.4 GHz for sample A……………51
Fig. 4-16 The output power, power gain and power added efficiency (PAE) characteristics versus input power at 2.4 GHz for sample B……………52
Fig. 4-17 The output power, power gain and power added efficiency (PAE) characteristics versus input power at 2.4 GHz for sample C……………53
Fig. 4-18 The minimum noise figure (NFmin) and the associated gain characteristics versus frequency for sample A……………54
Fig. 4-19 The minimum noise figure (NFmin) and the associated gain characteristics versus frequency for sample B……………55
Fig. 4-20 The minimum noise figure (NFmin) and the associated gain characteristics versus frequency for sample C……………56
Fig. 4-21 Extrinsic transconductance and saturation drain current density of sample A from 300K to 450K……………57
Fig. 4-22 Extrinsic transconductance and saturation drain current density of sample B from 300K to 450K……………58
Fig. 4-23 Extrinsic transconductance and saturation drain current density of sample C from 300K to 450K……………59
Fig. 4-24 The relationships between the extrinsic transconductance and temperature of our studied AlGaAs/InGaAs/GaAs HFETs……………60
Fig. 4-25 The relationships between the scattering mechanism and temperature……………61
Fig. 4-26 The relationships between the threshold voltage and temperature of our studied AlGaAs/InGaAs/GaAs HFETs……………62
Fig. 4-27 Two-terminal gate-drain breakdown voltage characteristics of sample A from 300K to 450K……………63
Fig. 4-28 Two-terminal gate-drain breakdown voltage characteristics of sample B from 300K to 450K……………64
Fig. 4-29 Two-terminal gate-drain breakdown voltage characteristics of sample C from 300K to 450K……………65
Fig. 4-30 RF characteristics of sample A from 300K to 420K……………66
Fig. 4-31 RF characteristics of sample B from 300K to 420K……………67
Fig. 4-32 RF characteristics of sample C from 300K to 420K……………68
Fig. 4-33 The relationships between the fT and temperature of our studied AlGaAs/InGaAs/GaAs HFETs……………69
Fig. 4-34 The relationships between the fmax and temperature of our studied AlGaAs/InGaAs/GaAs HFETs……………70

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