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Title of Thesis

Modeling Techniques of Submicron GaAs MESFETs and HEMTs

Author (s)
Noor Muhammad Memon
Institute/University/Department Details
Mohammad Ali Jinnah University, Karachi
Electrical Engineering
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
 mobility of carriers, Schottky barrier gate, interfacial layer


This thesis discusses the electrical response of submicron GaAs MESFETs and HEMTs to develop a physical model. Nine different FET models have been presented and their ability to simulate submicron GaAs MESFET characteristics are checked. To demonstrate the validity of a model, I-V characteristics of short channel MESFETs are simulated and compared with experimental data. The accuracy of a model is reported by evaluating its RMS error values. A comprehensive new model is developed to simulate I-V characteristics of short channel GaAa FETs. It has been demonstrated that the proposed model is a comprehensive one, capable of simulating DC characteristics of GaAs MESFETs including those having significant non-ideal Schottky barrier response. The model has also been applied successfully to I-V characteristics of GaAs HEMTs. The Schottky barrier interfacial layer dependent performance of submicron GaAs MESFETs has been discussed by using their output and transfer characteristics. The mobility of carriers, scattering from the channel into the Schottky barrier gate, increases significantly for the devices which have a relatively thicker interfacial layer. The negative effects of increased carriers’ mobility from MESFET Schottky barrier gate are discussed and a plausible explanation is given for reduced barrier lowering in the presence of interfacial layer. Based on the proposed explanation the definition of threshold voltage has been redefined involving the concept of interfacial layer thickness. A technique is developed to estimate intrinsic small signal parameters of GaAs MESFETs and HEMTs. In the proposed technique DC characteristics are first evaluated. Once a good DC match is attained then small signal parameters are evaluated. To check the validity of the proposed technique submicron GaAs MESFETs and HEMTs of varying gate length have been simulated. It has been shown that the proposed method is accurate as well as efficient in estimating AC parameters of GaAs FETs by using their DC characteristics, and could be employed as a useful tool in device simulation software.




2149 KB

S. No. Chapter Title of the Chapters Page Size (KB)
1 1 Introduction 1
  1.1 MESFET’s Overview 1
  1.2 GaAs MESFET Construction 4
  1.3 Types of MESFETs 7
190 KB
  1.4 MESFET Characteristics 10
  1.5 MESFET Models 12
2 2 MESFET’s Operation 15
  2.1 Introduction 15

327 KB


  2.2 Long Channel Model 16
  2.3 Short Channel Model 23
  2.4 Microwave MESFET’s Equivalent Circuit 25
  2.5 Summary 39
3 3 Nonlinear GaAs MESFET’s Models 40
  3.1 Introduction 40
  3.2 Curtice Model 43

400 KB

  3.3 Materka Model 45
  3.4 Statz Model 46
  3.5 McCamant Model 49
  3.6 Rodriguiz Model 53
4 4 Effects of Interfacial Layer on Submicron GaAs MESFET’s Characteristics 68
278 KB
  4.1 Introduction 68
  4.2 Effect of Interface States 69
  4.3 Evaluation of Interfacial Layer Thickness 72
  4.4 Thermionic Emission with Interfacial Layer 74
  4.5 Effects of Interfacial Layer on MESFETs Characteristics 75
5 5 A Comprehensive FET I-V Model 88


448 KB

  5.1 New Model  89

Effects of Fitting Parameters on GaAs MESFET’s DC Characteristics

  5.3 Simulated MESFET’s DC Characteristics 94
  5.4 Simulated HEMT’s DC Characteristics 98
  5.5 Summary 110
6 6 Extraction of AC Parameters 111
  6.1 Introduction 111
  6.2 MESFET’s and HEMT’s AC Parameters 112
  6.3 Estimated MESFET AC Equivalent Circuit Parameters 128
  6.4 Estimated HEMT AC Equivalent Circuit Parameters 131
  6.5 Summary 136




235 KB


7 7 Conclusion and Future Work  137