Advisor: R. F. Davis, MSE.
Solid-state lighting (SSL) is the direct conversion
of electricity to visible white light using semiconductor
materials and technology. This technology
has the potential for vastly improving the efficiency
of 21st century lighting via the replacement of
incandescent and fluorescent lighting with high
brightness light-emitting diodes (LEDs). The
use of LEDs avoids the indirect processes involving
either heat (incandescent lighting) or plasmas
and Hg vapor (fluorescent lighting). Lighting
accounts for ~22% of all energy utilization in
the USA. If a 50%-efficient LED technology
were to be developed, it would reduce energy consumption
in the U. S. by ~620 billion kilowatt-hours/year
and eliminate the need for ~70 new nuclear plants,
each generating a billion Watts of power. Infrared
LEDs with an efficiency of 76% have been recently
demonstrated; however, the efficiencies of blue
and green LEDs remain below 50%. Current
research in MSE at CMU is addressing the scientific
reasons for all the known causes of inefficiencies
in the green and blue LEDs, e.g., non-radiative
energy losses (1) at contacts, (2) in the n- and
p-regions of the device (especially under high
current injection), (3) in the active and quasi-neutral
regions of the device and (4) due to diffusion
of carriers through the active region without recombination.
The REU students involved in this program will
be trained to produce and characterize blue-and
green-emitting LEDs. The students will (1)
work with the graduate student conducting the growth
of the thin films and quantum wells that comprise
the device structure and the graduate student conducting
the deposition of contacts to these structures,
(2) characterize this structure using photoluminescence
and atomic force microscopy, (3) fabricate blue
and green LED devices using flip-chip technology
(4) and electrically and optically characterize
these devices using equipment available on the
CMU campus. |
