SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

8.4. HFETS: INTRODUCTION 377 or MOSFETs. A typical modulation doped device structure is shown in figure 8.13a. We show a structu ...

378 CHAPTER 8. FIELD EFFECT TRANSISTORS High Sheet Charge Density: The charge density in the 2-dimensional HFET channel de- pen ...

8.5. CHARGE CONTROL MODEL FOR THE MODFET 379 0.0 0.2 0.4 0.6 0.8 0.0 0.3 0.6 0.9 1.2 1.5 Drain voltage (V) Drain Current (A/mm) ...

380 CHAPTER 8. FIELD EFFECT TRANSISTORS eφb EF, m ΔEc E -eVG F, s eV 2 eV 1 eVdi- d -ds^0 Δd eVdi+ Z Z nm npar ns Nd+ Z 1 =-e ...

8.5. CHARGE CONTROL MODEL FOR THE MODFET 381 The charge distribution in the system is determined by electrostatics and can be va ...

382 CHAPTER 8. FIELD EFFECT TRANSISTORS It effectively acts as a voltage divider between the gate and source as the Fermi level ...

8.5. CHARGE CONTROL MODEL FOR THE MODFET 383 0 z EF E 0 E 1 V edi eV(z)=E 2 z−eVdi− Figure 8.16: Band structure of the HFET ...

384 CHAPTER 8. FIELD EFFECT TRANSISTORS The electric field in the buffer (or bulk) is zero. The voltages in the system are spec ...

8.5. CHARGE CONTROL MODEL FOR THE MODFET 385 therefore eΔns=  D ·(±Vg) This is the charge control equation of the gate capacito ...

386 CHAPTER 8. FIELD EFFECT TRANSISTORS eVG> 0 (a) (b) eφb EF, m |eVp| EF, s d -ds 0 + + + + + Ec EF, m d -ds^0 + + + + E ...

8.5. CHARGE CONTROL MODEL FOR THE MODFET 387 assumeΔnpar= ∫ 0 −dn(AlGaAs)dx→^0. From equation 8.5.9, we have ns(VG)= ( Nd−Nd^0 ) ...

388 CHAPTER 8. FIELD EFFECT TRANSISTORS The device is thus a depletion mode MODFET. The 2DEG carrier concentration is given by n ...

8.6. POLAR MATERIALS AND STRUCTURES 389 GaN Ga face N face (0001) -Qπ +Qπ +Qπ +Qπ -Qπ -Qπ} ΣQ=0 (a) -Qπ +Qπ (c) (b) +Qscr -Qscr ...

390 CHAPTER 8. FIELD EFFECT TRANSISTORS (a) (b) n-GaN Substrate Growth direction (0001) +Qπ -Qπ EF EC EV Defective region dcr 0 ...

8.6. POLAR MATERIALS AND STRUCTURES 391 n-GaN Substrate +Qπ -Qπ EF EC EV +eNDD (b) Defective region Ionized surface states + + + ...

392 CHAPTER 8. FIELD EFFECT TRANSISTORS n-GaN Substrate +Qπ -Qπ EF EC EV +eNDD (b) + EDD (a) 0 dGaN -Qscr ++ ++ ++ ++ 0 wd dGaN ...

8.6. POLAR MATERIALS AND STRUCTURES 393 eφs ΔEc V- EF edi eVdi+ Z ns eNDD+ (a) (b) (c) { { AlGaN GaN 2DEG dAlGaN 0 Δd dAlGaN D ...

394 CHAPTER 8. FIELD EFFECT TRANSISTORS SS G D Figure 8.23: Top view of an AlGaN/GaN HFET structure with 2 gate fingers. Picture ...

8.7. DESIGN ISSUES IN HFETS 395 the distributed charge as a 2 dimensional sheet charge of densityensa distanceΔdfrom the heteroi ...

396 CHAPTER 8. FIELD EFFECT TRANSISTORS Design Issues in HFET Technology DESIGNISSUE NEED METHODOLOGY Ohmic contact resistance ...