High Electron Mobility Transistors (HEMT)

BY: AARON BUEHLER &

JASON VANDERLINDE

Outline•Brief History

•What are they?•How they Work•Different Types• Band Structure and Diagrams

•Applications

•Key Points

•References

Brief History•Developed by Takashi Mimura and colleagues at Fujitsu in Japan in 1979•Faced several issues along the way •Early Applications: • Low noise amplifiers• Installed in radio telescope•Other space and military applications• Commercialization began in 1987 for satellite broadcasting receivers• Commercial production took off in the 90’s

What are they?•Referred to as heterojunction field-effect transistor (FET)•Abrupt discontinuities •Two layers of different semiconductor with two different band gap energies•Separating majority carriers and ionized impurities minimizes the degradation in mobility and peak velocity•The 2-D electron gas = less electron collisions = less noise

Different Types•Material: AlGaAs-GaAs•Pseudomorphic HEMT (pHEMT)•Metamorphic HEMT (mHEMT)•Indium Phosphide (InP)•Galium Nitride (GaN)

HEMT structure

pHEMT• GaAs pHEMT•< .5 µm gate length•Low noise: 1dB at 12GHz•High gain: 10 dB at 12GHz•Range up to 26GHz•Thin layer so the crystal lattice stretches to fit the other material. •Larger bandgap differences = better performance

mHEMT•.15 µm gate length•Low noise•High gain•Range up to 100GHz•Large lattice mismatch between the channel and substrate is accommodated by formation of dislocations within a metamorphic buffer.

Band Structure

AlGaAs-GaAs HEMT band diagrams

InP HEMT

Cross section using a scanning electron micrograph

GaN HEMT•Based on GaN/AlGaN heterojunctions

•Uses a Sapphire (Al3O2)/Silicon Carbonide(SiC) substrate because of the wide energy gap of 3.4 eV and 3.3 eV•Applicable to high power supply voltages because of the wide energy gaps•Can withstand high operating temperatures

Applications•Originally for high speed applications•High power/ high temperature microwave applications•Power amplifiers•Oscillators•Cell Phones•Radar•Most MMIC’s radio frequency applications

Key Points•Its two main features are low noise and high frequency capability•A heterojunction is two layers different semiconductors with different band gap energies•The 2-D electron gas is essential to the low noise feature•AlGaAs and GaAs are the most common materials for heterojunction•Used in MMIC’s and radio frequency applications for high performance

Sources•"GaAs Pseudomorphic HEMT Transistor." Mimix Broadband, Inc. N.p., 19 July 2008. Web. 30 Apr. 2013. <http://www.richardsonrfpd.com/resources/RellDocuments/SYS_4/CF003-

03.pdf>.

•Grunenputt, Erik. "Pseudomorphic and Metamorphic HEMT-technologies for Industrial W-band Low-noise and Power Applications.” Youscribe. N.p., Dec. 2009. Web. 30 Apr. 2013. <http://www.youscribe.com/catalogue/rapports-et-theses/savoirs/pseudomorphic-

and- metamorphic-hemt-technologies-for-industrial-w-band-1426512>.

•Poole, Ian. "HEMT, High Electron Mobility Transistor." Radio-Electronics.com. Adrio Communications, June 2010. Web. 30 Apr. 2013. <http://www.radio-electronics.com/info/data/semicond/fet-field-effect-transistor/hemt-phemt- transistor.php>.

Sources continued•"0.15-um LN MHEMT 3MI." TriQuint.com. N.p., 29 Nov. 2007. Web. <http://www.triquint.com/prodserv/foundry/docs/0.15.LN.mHEMT.3MI.pdf>.•Göran, Andersson, ed. "High Electron Mobility Transistors (HEMT)." Laboratory for Millimeter-Wave

Electronics. ETH Zurich, 2 Mar 2010. Web. 30 Apr 2013. <http://www.mwe.ee.ethz.ch/en/about-

mwe-group/research/vision-and-aim/high-electron-mobility-transistors-hemt.html>.•Neamen, Donald. Semiconductor Physics and Devices Basic Principles. 4th ed. New York: McGraw-Hill,

2012. 602-9. Print.•Mimura, Takashi. "The Early History of the High Electron Mobility Transistor (HEMT)." Early History of

the High Electron Mobility Transistor (HEMT). 50.3 (2002): 780-82. Web. 30 Apr. 2013. <http://ieeexplore.ieee.org.libpdb.d.umn.edu:2048/stamp/stamp.jsp?tp=&arnumber=989961&tag=1>.