Quantum cascade light emitting diodes based on type-II quantum wells Page: 4 of 9
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nSb aSb AISb
active region injection region
Figure 1. Schematic drawing of a n-type-QC structure based on type-I QWs.
The type-I QC light emitting diode (LED) was composed of 20 periods of active regions separated
by n-Type injection regions which serve both as the collectors for the preceding active regions and
emitters for the followng ones. As shown in Figure 1, the active region was composed of several
couples QWs, which were sequentially made of 23 A AlSb, 25.5 A InAs, 34 A InGaSb, and 15 A AlSb
layers. The injection region consists of digitally graded InAs/AlSb (InAlSb) QWs in which the InAs
layers are Si doped at 6x 1017 cnm, and the AlSb and IAlSb layers are undoped. The whole device
structure is strain balanced and lattice matched to the GaSb substrate. To improve the power efficieny,
we have been careful in the design of active regions and injection regions in order to minimize the losses
due to interband and intersubband absorption, and Auger recombination. Under a forward bias, electrons
are injected from an injection region into the level E, which is in the bandgap region of the adjacent
InGaSb layer. Since the electrons are effectively confined in the InAs well with the InGaSb, AlSb, and
GaSb barrier layers, they tend to relax to the hole state Eh in the adjacent valence band QW. The
resulting photon emissions are shown in Figure 1. Therefore, the leakage current is reduced. Electrons
at state Eh will then cross the thin ASb barrier and GaSb layer by tunneling and scattering into the
conduction band of the next injection region because of a strong spatial interband coupling (an unique
feature existed in Sb-based type-It heterostructure), and are ready for the next interband transition.
Since the relaxation time from E, to E, is much longer than the carrier transportation time at Eh, a
population inversion is easily established.
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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/m1/4/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.