Figure 2. Physical properties of ZnO microtubes.

1
Microwave Growth and Characterization of Zinc
Oxide Single Crystal Microtubes for
Optoelectronic Applications
Jiping Cheng Ruyan Guo, Pennsylvania State
University (DMR-0505946)

• A novel microwave growth technique has been used
  for fabrication of high quality and high purity
  ZnO single crystal microtubes with unique
  crystalline structure and excellent
  opto-electronic properties.
• The microwave grown ZnO microtubes are
  colorless, fully transparent, and of near-perfect
  crystallinity as shown in Fig. 1. The wall
  thickness of the ZnO microtubes is typically
  between 0.5-1 mm. By adjusting microwave growth
  parameters, the ZnO tubes can be fabricated into
  various cross-sectional dimensions ranging from
  100 to 250 mm and different length up to 5 mm.
• Some unique physical properties of ZnO single
  crystal microtubes shown in Fig. 2 indicate
  potential applications of ZnO microtubes in
  optoelectronic devices
• (A) The photoluminescence Spectra at
  room-temperature shows strong near band-edge
  emission for light emission applications deep as
  deep blue LEDs and laser diodes.
• (B) ZnO microtubes demonstrated high ultraviolet
  (UV) photoresponse that can be used as UV
  detection devices.
• (C) The strong electric field emission
  properties of the ZnO microtube reveal a
  promising application in flat panel display
  devices.
• P-type ZnO regions are formed successfully with
  verification of I-V characteristics. The
  significant results are the potential increase of
  solubility limit by the microwave-assisted plasma
  processing to make p-n junction on ZnO crystals
  for the optoelectronic applications.

Figure 1. SEM images of ZnO microtubes.
Figure 2. Physical properties of ZnO microtubes.
(A) Photoluminescence spectra. (B)
Photoresponse spectra. (C) Electrical field
emission properties.
2
Microwave Growth and Characterization of Zinc
Oxide Single Crystal Microtubes for
Optoelectronic Applications
Jiping Cheng Ruyan Guo, Pennsylvania State
University (DMR-0505946)

• Education and Outreach
• Paris Y. Liu, graduate student, passed her PhD
  candidacy exam and is making excellent progress
  in this research project conducting fabrication
  and characterization of p-n junction on ZnO
  crystals.
• Piezoelectric properties of ZnO microtubes are
  investigated using high precision optical
  interferometer method. Microtube ZnO is found to
  have larger d33 coefficient than bulk crystals.
• EE412 Optical Engineering Lab - the
  interferometric measurement set up has been
  adapted and added as an advanced optical
  engineering lab for the undergraduate students of
  Dept. of Electrical Engineering.
• Technology Transfer the project was represented
  at the Open House, Pennsylvania Center for
  Optical Technologies, 2005 and 2006.
• REU Hosting Lab tour for undergraduate students
  participating in NSF EEREU program (Dr. Guo
  serves as PI in EEREU program).
• Several talks on fabrication and characterization
  of ZnO microtubes and related crystal materials
  were presented at professional conferences.
• Collaborative Research Lehigh University and
  Penn State University have formed partnership
  through Center for Optical Technologies (COT),
  funded by the Commonwealth of Pennsylvania. The
  early effort developing the ZnO microtubes was
  supported through COT seed grant and
  collaboration.

Paris Y. Liu, a graduate student, is using the
microwave plasma PVD system to fabricate p-n
junction on ZnO single crystal materials.
The PI, Dr. Cheng, gives a invited talk entitled
Advancements in microwave fabrication of ZnO
crystal materials at the 2005 International
Workshop on Advanced Material held in Wuhan
University of Technology, China.