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UID:20260523T163852EDT-3177r0wFoA@132.216.98.100
DTSTAMP:20260523T203852Z
DESCRIPTION:Abstract\n\nLight emitting didoes (LEDs) through vertical curre
 nt injection offer numerous advantages including excellent heat dissipatio
 n and size scalability. Yet it remains difficult to realize AlGaN deep-ult
 raviolet (deep-UV\, wavelength shorter than 300 nm) LEDs through vertical 
 injection. Silicon (Si) substrates\, owing to their excellent conductivity
 \, easy to removal by chemical wet etching\, and mature manufacturing proc
 ess\, are a promising platform for developing vertical AlGaN deep-UV LEDs.
  Nevertheless\, obtaining high quality AlGaN epilayers on Si substrate has
  remained a challenge due to the large lattice and thermal mismatch betwee
 n AlN and Si. In this thesis\, we demonstrate a nanowire template assisted
  buffer layer technology on Si that enables high-quality AlGaN epilayers o
 n Si\, which further enables vertical AlGaN deep-UV LEDs.\n\nWe first perf
 orm the molecular beam epitaxial growth and characterization of AlN epilay
 ers on Si substrates using the nanowire template. Highly smooth AlN epilay
 ers with root-mean-square (rms) roughness of less than 0.4 nm are obtained
 . Our detailed comparison between the AlN epilayers grown on the nanowire 
 template and the AlN epilayers directly on Si confirms that the use of the
  nanowire template can improve the crystalline quality and relax the tensi
 le stress from Si. Using such AlN buffer layer\, AlGaN epilayers with Al c
 ontent varying from 35% to 70% are developed. The internal quantum efficie
 ncy (IQE) for such AlGaN epilayers are in the range of 30 - 40% under low 
 excitations.\n\nWith these material developments\, vertically injected\, s
 urface emitting AlGaN deep-UV LEDs down to 247 nm are demonstrated\, by fa
 r the shortest wavelength for deep UV LEDs on Si with AlGaN epilayers. To 
 further improve the device electrical performance\, we have explored the p
 olarization doped AlGaN epilayers on Si by grading the Al content along th
 e growth direction. Vertical LEDs emitting around 278 nm are realized\, an
 d with using the polarization enhanced doping\, the device series resistan
 ce is reduced by a factor of 5. This thesis work provides a viable path no
 t only for vertical semiconductor deep UV LEDs\, but also for low-cost ult
 rawide bandgap semiconductor template\, potentially impact both photonics 
 and electronic devices.\n
DTSTART:20230420T150000Z
DTEND:20230420T170000Z
LOCATION:Room 603\, McConnell Engineering Building\, CA\, QC\, Montreal\, H
 3A 0E9\, 3480 rue University
SUMMARY:PhD defence of Qihua Zhang – 'Molecular Beam Epitaxial Growth and C
 haracterization of AlGaN Epilayers for Vertical Deep Ultraviolet LEDs on S
 ilicon'
URL:/ece/channels/event/phd-defence-qihua-zhang-molecu
 lar-beam-epitaxial-growth-and-characterization-algan-epilayers-347617
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