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CATEGORIES:Colloquia / Seminar / Lecture
DESCRIPTION:Two-dimensional electron gas (2DEG) in the GaN semiconductor fa
 mily can be readily induced by polarization discontinuity without impurity 
 dopants at a heterointerface\, which is the heart of a high-electron mobili
 ty transistor (HEMT). Over the past decade\, GaN HEMTs have been employed i
 n 5G base stations\, faster and miniature battery chargers etc. thanks to t
 he high-speed operation and high power density afforded by this semiconduct
 or family.\n\nAs a fundamental departure from impurity-doping and modulatio
 n-doping\, the two well-known doping schemes in semiconductors\, polarizati
 on-induced three-dimensional electron gas in GaN was also postulated and ex
 perimentally demonstrated for the first time in 2002 [1]. Thanks to the adv
 ent of high-quality bulk GaN substrates\, polarization-induced three-dimens
 ional hole gas in GaN was demonstrated in 2010\, with assistance of impurit
 y dopants\; for the first time\, p-type conductivity in GaN was measured do
 wn to cryogenic temperatures\, 4 Kelvin [2]. This was nearly an impossible 
 feat in impurity-doped p-type GaN due to carrier freeze-out. It has been ab
 out 20 years since the existence of mobile holes in GaN heterostructures wi
 thout impurity dopants\, the counterpart of 2DEG\, was postulated. Only rec
 ently\, undisputable experimental observations are achieved in our lab [3].
  \n\nThe long-missing polarization-induced two-dimensional hole gas (2DHG) 
 is finally observed in undoped gallium nitride quantum wells. Experimental 
 results provide unambiguous proof that a 2D hole gas in GaN grown on AlN do
 es not need impurity doping\, and can be formed entirely by the difference 
 in the internal polarization fields across the semiconductor heterojunction
 . The measured 2D hole gas densities\, about 4x1013 cm-2\, are among the hi
 ghest among all known semiconductors and remain unchanged down to cryogenic
  temperatures. Some of the lowest sheet resistances of all wide-bandgap sem
 iconductors are seen. The observed results provide a new probe for studying
  the valence band structure and transport properties of wide-bandgap nitrid
 e interfaces\, and simultaneously enable the missing component for gallium 
 nitride-based p-channel transistors for energy-efficient electronics.\n\nRe
 ferences: 1) D. Jena\, H. Xing et al.\, Appl. Phys. Lett. 81(23)\, 4395-439
 7 (2002). DOI: 10.1063/1.1526161 2) J. Simon\, H. Xing\, D. Jena et al.\, S
 cience 327\, 60 (2010) DOI: 10.1126/science.1183226 3) R. Chaudhuri\, H. Xi
 ng\, D. Jena et al.\, Science 365\, 1454 (2019) DOI:10.1126/science.aau8623
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DTEND:20201016T201500Z
DTSTAMP:20260411T110608Z
DTSTART:20201016T190000Z
LOCATION:Zoom
SEQUENCE:0
SUMMARY:The Hunt for Mobile Holes Induced by Polarization in GaN
UID:tag:localist.com\,2008:EventInstance_34536561546413
URL:https://events.seas.harvard.edu/event/guest_speaker_grace_xing_cornell_
 university
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