SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

8.2. JFET AND MESFET:CHARGE CONTROL 357 Figure 8.1: MESFETs and JFETs are important devices for high-speed, low-noise amplifiers ...

358 CHAPTER 8. FIELD EFFECT TRANSISTORS Gate controlled carrier density in the channel Source Drain Gate Figure 8.2: The physica ...

8.2. JFET AND MESFET:CHARGE CONTROL 359 Ga te ( p+ or Sc ho ttk y ba rri er ) So ur ce Dr ai n n-d op ed se mi co nduc to r lo w ...

360 CHAPTER 8. FIELD EFFECT TRANSISTORS ID ID ID VGS = 0 negative VGS large negative VGS Linear I-V VDS VDS Suppression of curre ...

8.2. JFET AND MESFET:CHARGE CONTROL 361 VDS =VDS1 VDS =VDS2>VDS1 ID ID ID VGS = V VGS = V VDS VDS VDS VDS =VDS3>VDS2 VGS = ...

362 CHAPTER 8. FIELD EFFECT TRANSISTORS This gives Js=8×(300)^2 × 4. 34 × 10 −^14 =3. 125 × 10 −^8 A/cm^2 For thep+-gate we have ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 363 n- GaAs Ec – EF EF Ev Ec Source (ohmic) Gate (Schottky) Drain (ohmic) eVbi eφb Semi- in ...

364 CHAPTER 8. FIELD EFFECT TRANSISTORS n+ Conducting channel Substrate SDG Conducting channel Substrate G (a) (b) n+ n+ n+ Sour ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 365 The current in the drain is given by (field =−dV /dx) ID = channel area×(charge density ...

366 CHAPTER 8. FIELD EFFECT TRANSISTORS (a) S G D Semi-insulating substrate Z h x L W(x) EFn (drain) EFn (source) Quasi-linear d ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 367 and the saturated channel current becomes, from equation 8.3.7 (the drain current does ...

368 CHAPTER 8. FIELD EFFECT TRANSISTORS Saturation region Locus for VDS(sat) Linear region VB VDS 0 VGS = 0 VGS> 0 VGS< 0 ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 369 Figure 8.10a shows a schematic diagram of the FET depletion profile whenVDS>VDS(sat) ...

370 CHAPTER 8. FIELD EFFECT TRANSISTORS W(x) δ SGD LI LII h EFn (drain) EFn (source) (a) (b) Semi-insulating substrate x Region ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 371 LII x gate + + + + + + + + + + + + + + + + + + + + + + + + + + + + + drain 0 x (x) (a) ...

372 CHAPTER 8. FIELD EFFECT TRANSISTORS underconsideration, can be readily shown to be the gradual channel solution of the deple ...

8.3. CURRENT-VOLTAGE CHARACTERISTICS 373 VD ID Vdp VDS(sat) slope = gd Figure 8.12:IDvs.VDfor constantVG. VD(or a large output c ...

374 CHAPTER 8. FIELD EFFECT TRANSISTORS whereCGis assumed to be constant (which is true for a MOSFET) and is the normalized capa ...

8.4. HFETS: INTRODUCTION 375 and V(LII,h)=VD (8.3.37) The voltage drop in the pinched region (Region II) isVD−(VG−VT)orVD−VDS(sa ...

376 CHAPTER 8. FIELD EFFECT TRANSISTORS Source Gate Drain Undoped GaAs 2DEG n+ GaAs n+ Al GaAs A GaAsl Undoped Semi-insulating G ...