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High Electron Mobility Transistors

Abstract: HEMT is a field effect transistor incorporating a junction between two materials with different band gaps as the channel. We will discuss different types of HEMTs and their Applications. High Electron Mobility Transistors.

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High Electron Mobility Transistors

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  1. Abstract: HEMT is a field effect transistor incorporating a junction between two materials with different band gaps as the channel. We will discuss different types of HEMTs and their Applications. High Electron Mobility Transistors Presented by: Date: 04/28/2014 SujanaKorrapati, SaiDivya Anne

  2. Outline • Introduction • GaN HEMT structure and operation principles • Design rules for AlGaN/GaN HEMT • InP HEMT • Comparison of GaN HEMT with GaAs HEMT • Applications in Technology • Summary

  3. Introduction • Transistors are used in electronic devices e.g. switch, amplifiers, oscillators • To satisfy the growing demands of • High Power • High Speed • High Efficiency communications • Conventional HEMTs use a AlGaAs/GaAsAlGaN/GaN

  4. Basic GaN HEMT Structure Source: http://www.eetimes.com/document.asp?doc_id=1272514

  5. Gallium Nitrate • High electron density(Polarization effects) • Adequate for high power amplifiers High Breakdown voltage • Large heat capacity • Necessary to growth in a wafer of another material • Molecular Beam Epitaxy • Metal Organic Vapor Beam Epitaxy

  6. Substrate Material • Sapphire • Most used material, cheap, good quality commercial wafers. • Poor thermal conductivity. • Silicon Carbide • Low lattice mismatch. • High thermal capacity. • Silicon • Most common semiconductor. • Acceptable thermal conductivity.

  7. Operation principles (Polarization) AlGaN/GaN HEMTs transistor don’t need doping to obtain a high electron density. Spontaneous polarization. + Piezoelectronic polarization. = 1013 (cm2/Vs) carrier concentration

  8. Enegry Band Diagram of GaN/AlGaN HEMT • HEMTs utilize heterojunction between two semiconducting materials to confine electrons to a triangular quantum well.  • Conduction band edge EC and Fermi level EF determine the electron density in the 2DEG Source:http://research.pbsci.ucsc.edu/chemistry/li/research.html

  9. Heterojunction • Heterojunction: 2 layers • Highlydoped layer with grand gap • Non-doped layer withsmall gap

  10. Design Rules ForGaN/AlGaN HEMTs:Materials Perspective • Thickness of the Barrier Layer • Al composition of the barrier layer • Nucleation and Buffer layer • Substrate for epitaxial growth

  11. Design Rules ForGaN/AlGaN HEMTs:Fabrication Perspective • Gate footprint, cross-sectionalarea andwidthcontrols thefrequency response • Gate drain spacingaswellasgatefootprintdeterminesthebreakdownvoltage • Geometryofthedevice alsoplaysarole

  12. DC characteristics of GaN/AlGaN HEMTs

  13. InP HEMT Source: http://www.mwe.ee.ethz.ch/en/about-mwe-group/research/vision-and-aim/high-electron-mobility-transistors-hemt.html

  14. Advantages of InP based HFETs • Lower noise • Higher cutoff frequency • Higher gain • Operating voltage below 3 V

  15. Comparison of GaN HEMT with GaAs HEMT ΦB GaN AlGaN Ec ∆Ec EF d AlGaAs donor σcomp σB +ve GaAs buffer layer 2 DEG σsurf AlGaAsspacer AlGaN/GaN HEMT AlGaAs/GaAsHEMT

  16. HEMT Applications • A Monolithic HEMT Passive Switch for Phased- Array Applications • High Power and High Efficiency GaN-HEMT for Microwave Communication Applications • Highly efficient high power InP HEMT amplifiers for high frequency applications • Highly Uniform InAlAs–InGaAs HEMT Technology for High-Speed Optical Communication System ICs

  17. A Monolithic HEMT Passive Switch for Phased- Array Applications A 0.2 x 200 ,um2 HEMT device is used as a series passive FET switch

  18. High Power and High Efficiency GaN-HEMT for Microwave Communication Applications In the typical mobile communication band of more than 2GHz, the RF signal loss through the Cds and Rs becomes significant. Thus, the minimization of Cds is effective in the high efficiency amplification.

  19. InAlAs–InGaAs HEMT Technology for High-Speed Optical Communication System ICs • Uniformity of the transistors is required to fabricate high-speed ICs • ICs with more than 1000 transistors were fabricated using Y-shaped gate technology and operated at 40 Gb/s

  20. Summary & Conclusions • HEMT transistor are widely used in electronic application • AlGaN/GaN structure looks promising • AlGaN/GaN HEMT grown on Si substrate not only reduces the production cost but also prepares for the possible combination of GaN devices and Si technology

  21. References • http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=536950 • http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5877127 • http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1219481 • “Characterization of advanced AlGaN HEMT structures” Anders Lundskog. • http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=877122

  22. Five Key Points about HEMT • 3 contacts: Source and drain ohmic contacts. GateSchottky barrier • Conventional HEMTs use a AlGaAs/GaAsAlGaN/GaN • High electron density (Polarization effects) • The HEMT-HBT monolithic microwave integrated circuit (MMIC) is fabricated using selective molecular beam epitaxy (MBE) • InAlAs-InGaAs HEMT grown on InP substrate promises excellent gain and noise performance for amplifier applications

  23. Questions ??

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