[BNC-all] SEMINAR ANNOUNCEMENT: THURS. Feb 1; 10:30 AM; BRK 1001 . . . Sangho Kim, "Hexagonal Prism Blue Diode Laser Using Whispering Gallery Mode (WGM) Resonances"

[Starewich, Deborah S.]

Hexagonal Prism Blue Diode Laser Using Whispering Gallery Mode (WGM) Resonances

Thursday, February 1, 2007
Birck Nanotechnology Building, Room 1001
10:30 A.M.

Sangho Kim
Purdue University

Semiconductor lasers have many important applications, including communication
technologies, optical storage, printing, and molecular detection. The range of
applications could be broadened significantly if the lasers could be made
smaller and with lower threshold currents. Today’s in-plane semiconductor diode
lasers are large discrete devices (about 100 x 400 microns), a form factor that
results in part from the performance requirements associated with the optical
cavity. To reduce the cavity length, it is necessary to increase the
reflectivity of the mirrors – for example, by cleaving the crystal and coating
the facets with a dielectric multilayer - adding complexity to the fabrication
process. Although high-performance vertical cavity lasers can be fabricated from
III-V semiconductor heterostructures, the requisite high reflectivities of the
mirrors necessitate the fabrication of multilayers with hundreds of periods and
thickness control on the order of 1% or better.

An alternative design that permits a smaller cavity and active region with a
simple fabrication process is the hexagonal prism laser diode. With the
hexagonal cavity geometry, whispering gallery mode (WGM) resonances are
established by total internal reflection (TIR), which alleviates the need for
multilayer reflector coatings as required for small in-plane and vertical cavity
lasers. In addition, the high reflection efficiency from TIR enables a lower
current density threshold, which is of great utility from a device perspective.
The WGM resonance path for two-dimensional hexagonal devices allows reduced
device sizes (~2.6x) while maintaining resonance lengths equivalent to
one-dimensional in-plane lasers.

Hexagonal prism lasers were fabricated by reactive ion etching of (In,Ga)N
multi-quantum-well light-emitting diode heterostructures designed to emit in the
blue portion of the spectrum, Unlike the optically-pumped microdisk lasers that
have been reported recently, the 160 micron diameter hexagonal prism laser is
electrically-pumped and demonstrates lasing at 480nm (+/-5nm) with a threshold
voltage and current density of 9V and 7kA/cm2, respectively.  The performance of
these hexagonal prism diode lasers is expected to improve significantly with the
further development of a selective growth process to fabricate self-organized
hexagonal prism structures.

Bio

Sangho Kim is a Ph.D. student in the Electrical and Computer Engineering
department at Purdue University.  He is advised by Prof. Timothy D. Sands and
supported in part by the Institute for Nanoelectronics and Computing (INAC). Mr.
Kim received his B.E. degree in 1998 from Kwangwoon University, South Korea and
a M.S. degree in 2002 from Purdue University. His main research interest is in
the field of low threshold UV/blue lasers for optoelectronic integrated circuits
and sensors.

SPONSORED BY:
Birck Nanotechnology Center, Bindley Bioscience Center, Discovery Park, The NASA
Institute for Nanoelectronics and Computing, The Network for Computational
Nanotechnology, VEECO, NCN Student Leadership Council, Department of Chemistry,
Department of Physics, School of Chemical Engineering, School of Electrical and
Computer Engineering, School of Mechanical Engineering
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