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3.3-4.3
μm
high brightness LEDs
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- B. A. Matveev, N. V.
Zotova, N.D.Il’inskaya, S. A. Karandashev, M. A. Remennyi, N. M. Stus’
and V.V.Shustov
- Ioffe Physical-Technical Institute,
Polytechnicheskaya 26, 194021, St.Petersburg, Russia.
- FAX: (812) 297 7446, e-mail: bmat@iropt3.ioffe.rssi.ru,
http://www.mirdog.spb.ru
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Recent years have seen
extensive research of the mid-IR (2-5 um) diodes and resonant cavity LEDs
[1] as well as conventional LEDs including those with immersion lenses have
already broken the 1 mW output power barrier that is necessary for most
practical applications. However, curtain applications, such as spectroscopic
measurements with gratings and detector system calibration, call for high
brightness/apparent temperature rather than high power devices and thus the
latter should be free of lenses that magnify the image dimensions. LEDs with
flat out-coupling surface emitting at 3.3-3.6 um at room temperature have
already shown the ability to simulate the black body heated up to 593 K
(positive contrast dt = 300 K in the 3-5 um range ) [2, 3]. In spite of high
output power values that could be found in the literature for the flat
uncoated LEDs it is clear that there is still a room for chip design and
device performance improvements.
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Deep mesa that narrows the
internal radiation diagram due to the reflections from the inclined mesa
sidewalls contribute to the out-coupling enhancement and is thus a useful
feature of the high brightness sources. The effect of the above geometrical
factor is well known for the InSb (6 um) negative luminescent devices [1]
and efficient NIR and visible LEDs. However, to the best of our knowledge
there have been no attempts so far to investigate the impact of the mesa
dimensions/shape on the output power in a Mid-IR LED with wavelengths
shorter than 6 um.
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We report on double
heterostructure (DH) LEDs grown onto heavily doped n+-InAs
or undoped n-InAs substrates with 2-7 um thick active layers formed from n-InAs
(3.3 um) or n-InGaAsSb (3.7 um) or n-InAsSb (4.3 um) and p-InAsSbP claddings
(for all LED types). DHs were treated by two stage wet photolithography
process that enable us to achieve 10-40 um high sidewalls in a 250 um wide
mesas with a 50-210 um wide circular Au-anode in a flip-chip device.
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Common features of the
fabricated LEDs were superluminescence and blue shift of the emission
spectrum at 77 K due to dynamic Moss-Burstein effect, current/emission
crowding above the anode contact at 300 K and superiority of the negative
luminescence power conversion efficiency over the forward one at elevated
temperatures (say, at 480 K) due to suppression of the Auger recombination
in a depleted active layer.
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The report will focus on the
discussion of experimentally observed impact of several geometrical factors
(active layer thickness, mesa and contact diameter and side wall height) on
near and far field patterns, emission spectrum and output power including
the best achieved light extraction enhancement factor of 2 for the InAsSb
LEDs and apparent temperature contrast of dt=400 K (I=1 A) in the 3-5 um
band for the InAs LEDs.
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References
- [1]
A.M.Green et al , Physica E: Low-dimensional Systems and Nanostructures,
Vol. 20(3-4), pp. 531-535 (2004)
- [2] Naresh C. Das et al, Proc. of SPIE Vol.
5408, pp.136-143 (2004)
- [3] V.
Malyutenko et al , MIOMD –VI digest , pp.77-78, St.Petersburg, Russia, 28
June–2 July 2004
- [4] G.R.Nash et
al , Physica E: Low-dimensional Systems and Nanostructures, Vol. 20(3-4),
pp. 540-547 (2004)
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