Quantum cascade light emitting diodes based on type-II quantum wells Page: 5 of 9
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SPACE VACUUM EPITAXY CENTER UH 4 5058448985
- .-.- . q
U I I
I * I
-80 -60 -40 -20 0 20 40 60
Theta (minutes of arc)
Figure 2.004 DCXRD spectum of a type-if QC device.
The type-Il QC LEDs were grown in a Riber 32 molecular beam epitaxy (MBE) system on a p.-
type GaSb substrate using an EPI As valved cacker cell and an EPI Sb cracker cell. A 3000-A GaSb
buffer layer adjacent to the substrate was grown at 510 OC, The InAs/AISb cladding layers and the active
region was grown at 440 C. During the growth, the GaSb layers displayed good lx 3 tefection high-
energy electron diffraction (RHEED) pattern and the IrAs layers exhibited good 2x RREED patterns.
After growth. the sample was anmzaled at 490 C for 10 minutes, Growth rates were calibrated to within 2
% using RHEED and were connflmed by double-crystal x-ray diffraction (DCXRD) measurements. The
background doping density was lcw It' P 4 n-type for InAs and was about 2x10" cn' p-type for
GaSb. Using the same growth rate for Ins and GaSb, the background Sb in InAs layers was less than 1%
and the background As in GaSb was less han 3%. with a V/I BEP ratio of 3 for iAs and 2 for GaSb.
The BEP ON/OFF ratio with shutters opened or closed was about 8 for As2, and was about 160 for Sbi.
When the Sb/Ga V/IT BEP ratio was increased, the background As in GaSb decreased. However, the
background Sb in InAs layers was not sensitive to the As flux, This implies that the sticking coefficient of
background Sb in nAs at 440 C is almost 100%. From photoluminescence (PL) spectra, the material
quality of GaSb/A]Sb QWs is not sensitive to the Sb/Ga V/1I1 BEP ratio as long as the ratio is larger than
1.8. In order to improve the layer thickness and composition controL, we have also investigated the flux
transients of In, Ga, and Al effusion cells due to shutter operations [21. Using the EPI SUMO cells Ibr In
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Lin, C. H.; Yang, R. Q.; Zhang, D.; Murry, S. J.; Pei, S. S.; Allerman, A. A. et al. Quantum cascade light emitting diodes based on type-II quantum wells, article, January 21, 1997; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc674274/m1/5/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.