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which is a well-known problem that the internal quantum
efficiency (IQE) decreases with the increasing injection
current.
The reasons of the droop, may stem from the electron
overflow, Auger recombination, or insufficient hole
injection.
For example, hole transport and distribution improvement
across the multiple quantum wells (MQWs) have been
considered both theoretically and experimentally through
the quantum barrier (QB) architecture design, including pdoped QBs, p-InGaN as last QB, and a graded indium
composition in the QBs.
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Unfortunately, the growth windows to realize these QB
designs are quite narrow. In the design of the p-doped QBs
or the p-InGaN as the last QB, the magnesium dopants
could easily diffuse into the QW during the growth of the
p-doped QB, which will induce nonradiative recombination
centres and, hence, reduce the efficiency.
In this work, we present both experimental and theoretical
results on the advantage of QBs with a graded thickness in
homogenizing the hole distribution and suppressing the
efficiency droop.
In addition, here, we show that the LED with graded
barriers design could outperform the LED with equal
barrier thickness design only in the high-current regime,
which was not revealed in the previous reports.
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schematic diagrams of the (a) Equal-thickness quantum barrier(ETQB) LEDs
and (b) graded-thickness quantum barrier(GTQB) LEDs.
(a) ETQB LEDs
200nm p-GaN layer
12nm 800 ℃
30nm p-Al0.2Ga0.8N EBL
3nm 750℃
12nm 800 ℃
5-pair MQW
3μm Si-doped n-GaN layer
(b) GTQB LEDs
6.0nm
3nm
6.6nm
3nm
7.2nm
3nm
HT 5μm u-GaN
~150nm u-GaN interlayer
LT 30nm u-GaN buffer
Sapphire
12nm
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