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. Presented by: Date: 04/28/2014 Sujana Korrapati, Sai Divya Anne

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

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

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

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

Substrate Material Sapphire Silicon Carbide Silicon 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.

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

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

Heterojunction Heterojunction: 2 layers Highly doped layer with grand gap Non-doped layer with small gap

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

Design Rules For GaN/AlGaN HEMTs: Fabrication Perspective Gate footprint, cross-sectional area and width controls the frequency response Gate drain spacing as well as gate footprint determines the breakdown voltage Geometry of the device also plays a role

DC characteristics of GaN/AlGaN HEMTs

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

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

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

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

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

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.

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

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

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

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

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