Proceedings Article | 9 February 2011
Proc. SPIE. 7954, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XV
KEYWORDS: Surface plasmons, Quantum wells, Light emitting diodes, Polarization, Electrons, Quantum efficiency, Electroluminescence, Transmission electron microscopy, Gallium nitride, Dielectric polarization
We had demonstrated several novel methods to improve efficiency droop behavior in GaN-based light-emitting
diodes (LEDs). LEDs with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer
and n-GaN layer were investigated. By using low-temperature (LT, 780°C) n-GaN as IL, the efficiency droop behavior
can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA,
which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices (SPS) layer. The
polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect
density, about 5.3×108 cm-2, in its MQWs region is much higher than that value of 2.9×108 cm-2 in LED with LT n-GaN
layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this
alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of
polarization field. At second part, LEDs with graded-thickness multiple quantum wells (GQW) was designed and found
to have superior hole distribution as well as radiative recombination distribution by simulation modeling. Accordingly,
the experimental investigation of electroluminescence spectrum reveals additional emission from the previous narrower
wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current
density of 30 A/cm2 to 200 A/cm2. Moreover, the light output power is enhanced by 35% at 20 A/cm2.