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CALIFORNIA STATE UNIVERSITY, NORTHRIDGE A COMPREHENSIVE MODEL OF FREQUENCY DISPERSION OF GALLIUM NITRIDE MESFET A graduate project submitted in partial fulfillment of the requirements For the degree of Master of Science in Electrical Engineering By Rumman Raihan August 2018 Copyright by Rumman Raihan 2018 ii The graduate project of Rumman Raihan is approved: …………………………………….. ……………. Dr. Sembiam Rengarajan Date ……………………………………. …………….. Dr. Jack Ou Date ……………………………………… …………… Dr. Somnath Chattopadhyay, Chair Date California State University, Northridge iii ACKNOWLEDGEMENT At the very beginning, I would like to express my best and foremost gratitude towards Dr. Somnath Chattopadhyay for his help and guidance not just in this project, but also throughout my entire Graduate study period. He opened the door of his vast knowledge towards me and I am very much thankful to him for letting me work under his supervision. I also forward my gratitude towards Dr. Sembiam Rengarajan and Dr. Jack Ou to be on the graduate committee and spending their valuable time to guide me throughout the project. I express my love and gratitude to my mother and my family, my uncle Mr. Mohammad Islam and his family for their mental and financial support. iv DEDICATION This work is dedicated to my departed father Mr. K. M. Nur-ul-Alam (may his soul rest in peace) and my loving mother Mrs. Nilufa Akter. v TABLE OF CONTENTS COPYRIGHT PAGE..…………………………………………………………….............ii SIGNATURE PAGE..….…………………………………………………………...........iii ACKNOWLEDGEMENT…………………………………………………......................iv DEDICATION.....................................................................................................................v TABLE OF CONTENTS..………………………………………………………..............vi LIST OF FIGURES......................…………………………………………………........viii LIST OF TABLES..............................................................................................................ix ABSTRACT....………………………………………………………………………..…...x CHAPTER 1 1.1 INTRODUCTION ……………………………………………………………...…….1 1.2 FREQUENCY PERFORMANCE BETWEEN GaN AND SiC DEVICES …………3 1.3 SWITCHING PERFORMANCE BETWEEN GaN AND SiC DEVICES …………..5 1.4 POWER PERFORMANCE BETWEEN GaN AND SiC DEVICES …………...........8 1.5 GaN SUBSTRATE PREFERANCES ..........................................................................9 1.5.1 Sapphire .......................................................................................................10 1.5.2 SiC................................................................................................................11 1.5.3 Silicon...........................................................................................................11 1.5.4 Diamond........................................................................................................11 1.6 GaN IN OPTOELECTRONIC DEVICES...................................................................11 1.7 ADVANTAGES OF GALLUIM NITRIDE MATERIAL …….................................11 1.8 COMPARISON OF GALLIUM NITRIDE FETS......................................................13 1.9 APPLICATIONS OF GALLIUM NITRIDE DEVICES…………………………….14 1.9.1 Point of load converters.…………………………………………………...14 1.9.2 Monolithic motor drive.……………………………………………………14 1.9.3 Discrete motor drive.……………………………............………………....14 1.9.4 Automotive applications…………………………………………………...14 vi 1.10 RADIATION EFFECT ON GaN.............................................................................14 1.10.1 Damage in GaN for different types Radiations.........................................15 1.10.2 Comparison of radiation hardness between GaN and SiC.........................16 CHAPTER 2 2.1 GALLIUM NITRIDE MATERIAL PROPERTIES………………………………....18 2.2 FUNDAMENTAL PROPERTIES………………………………………………......19 2.3 BAND STRUCTURE..................................................................................................20 2.4 ENERGY BAND GAP................................................................................................22 2.5 ENERGY BANDGAP VERSUS LATTICE CONSTANT COMPARISON.............23 2.6 INTRINSIC CARRIER CONCENTRATION............................................................23 2.7 P-N JUNCTION BUILT-IN POTENTIAL.................................................................25 CHAPTER 3 3.1 GALLIUM NITRIDE MESFET DEVICES................................................................26 3.2 GaN MESFET PLANER STRUCTURE.....................................................................26 3.3 OPERATION OF GAN MESFET DEVICES.............................................................27 3.4 BREAKDOWN VOLTAGE........................................................................................28 3.5 ON-STATE RESISTANCE.........................................................................................29 CHAPTER 4 4.1 TRAPPING EFFECT..................................................................................................32 4.2 TRAPPING EFFECT ON I-V CHARACTERISTICS................................................35 4.3 TRAPPING EFFECT ON TRANSCONDUCTANCE...............................................37 4.4 RESULT AND DISCUSSION....................................................................................38 CHAPTER 5 CONCLUSION..................................................................................................................42 REFERENCES..................................................................................................................43 APPENDIX-CODES.........................................................................................................47 vii LIST OF FIGURES Figure 1.1 Areas of applications for silicon, gallium nitride and silicon carbide................4 Figure 1.2 Drift velocity versus applied electric field of different semiconductors............6 Figure 1.3 Drain current versus Drain to source voltage plot for FETs made with different semiconductors....................................................................................................................7 Figure 1.4 Comparison of switching performance among Si, SiC, GaN, GaAs..................7 Figure 1.5 Bandgap versus lattice constants for IV-IV, III-V and II-VI materials ...........10 Figure 1.6 Output characteristics for SiC and GaN devices before and after radiation.....16 Figure 1.7 Drain current vs gate to source voltage plot GaN and SiC devices before and after radiation.....................................................................................................................17 Figure 2.1 GaN wurtzite and zincblende structure............................................................18 Figure 2.2 Band structure of wurtzite GaN........................................................................20 Figure 2.3 Band structure of zincblende GaN...................................................................21 Figure 2.4 GaN crystal structure........................................................................................21 Figure 2.5 Energy bandgap vs temperature for Si, SiC and GaN......................................22 Figure 2.6 Energy bandgap versus lattice constant............................................................23 Figure 2.7: Intrinsic carrier concentration versus temperature..........................................24 Figure 2.8 Built in potential vs temperature......................................................................25 Figure 3.1: Planer structure of a GaN MESFET (simulated)............................................26 Figure 3.2: Comparison of Depletion and Enhancement mode MESFET .......................28 Figure 3.3 Resistance is a lateral junction MESFET.........................................................29 Figure 4.1 A MESFET structure........................................................................................32 Figure 4.2 I-Vds graph........................................................................................................39 Figure 4.3 gm vs Vgs plot for different Vds..........................................................................40 Figure 4.4 gm vs Vgs plot for different channel thickness...................................................41 viii LIST OF TABLES Table 1.1 Physical properties of different semiconductors................................................12 Table 1.2 Comparison between different GaN FETs.........................................................13 Table 2.1 Semiconductor fundamental properties comparison..........................................19 ix ABSTRACT A COMPREHENSIVE MODEL OF FREQUENCY DISPERSION OF GALLIUM NITRIDE MESFET By Rumman Raihan Master of Science in Electrical Engineering A physics based analytical modeling for Gallium Nitride (GaN) MESFET has been developed in this project to calculate drain to source current versus drain to source voltage and the transconductance with and without traps centers using MATLAB software. The drain-bias dependence of trapped carrier concentration has been calculated and incorporated in drain current and transconductance to study the traps behavior on drain current and transconductance. The drain current has been developed by two sets of equations for non-saturation and saturation current components and two current equations have been merged by optimizing different physical parameters. Hence, the current clearly shows linear and non-linear properties to validate the device performance. The transconductance has been derived from the derivative