GaN-based resonant-cavity light-emitting diode (RCLED) has a circular output beam with superior directionality than
conventional LED and has power scalability by using two-dimensional-array layout. In this work, blue RCLEDs with a
top reflector of approximately 50% reflectance were fabricated and characterized. An output power of more than 0.5 mW
per diode was achieved before packaging under room-temperature continuous-wave (CW) operation. The full width at
half maximum (FWHM) of the emission spectrum was approximately 3.5 and 4.5 nm for 10- and 20-μm-diameter
devices, respectively. And the peak wavelength as well as the FWHM remained stable at various currents and
Crack-free GaN-based light-emitting diodes (LEDs) were grown on 150-mm-diameter Si substrates by using low-pressure metal-organic chemical vapor deposition. The relationship between the LED devices and the thickness of quantum barriers (QBs) was investigated. The crystal quality and surface cracking of GaN-on-Si were greatly improved by an AlxGa1−xN buffer layer composed of graded Al. The threading dislocation density of the GaN-on-Si LEDs was reduced to <7×108 cm−2, yielding LEDs with high internal quantum efficiency. Simulation results indicated that reducing the QB thickness improved the carrier injection rate and distribution, thereby improving the droop behavior of the LEDs. LEDs featuring 6-nm-thick QBs exhibited the lowest droop behavior. However, the experimental results showed an unanticipated phenomenon, namely that the peak external quantum efficiency (EQE) and light output power (LOP) gradually decreased with a decreasing QB thickness. In other words, the GaN-on-Si LEDs with 8-nm-thick QBs exhibited low droop behavior and yielded a good peak EQE and LOP, achieving a 22.9% efficiency droop and 54.6% EQE.
In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been
demonstrated. By using a micro-photoluminescence (μ-PL) system operated at 77 K, the dominant resonant modes of the
GaN-based PC defect cavities show high quality factor (Q) values in the light emission performance which can be up to
4.3×103. Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect
cavities was measured to achieve around 64 % along the m crystalline direction.
We use thinner-quantum well to improve the droop behavior of GaN-base light emitting diode in simulation. Taking the advantage of that the thin quantum well will saturate easily, this characteristic of thin well will improve carrier distribution. Furthermore, this structure has more wave-function overlap than that of the thick well. This simulation result showed that decreasing the well thickness in specific position will not only improve the holes transport but also increase the quantum efficiency at high current density in the active region, and the efficiency droop behavior can be effectively suppressed. In this research, we designed three thin well structures by inserting different numbers of thin wells in the active region. We have compared them to the conventional LEDs, for which, the well thickness of 2.5 nm is used. The thin well structures have better droop behavior than conventional LED.
We present a study of semi-polar (1-101) InGaN-based light emitting diodes (LEDs) grown on
patterned (001) Si substrates by atmospheric-pressure metal organic chemical vapor deposition. A
transmission electron microscopy image of the semi-polar template shows that the threading
dislocation density was decreased significantly. From electroluminescence measurement,
semi-polar LEDs exhibit little blue-shift and low efficiency droop at a high injection current
because the reduction of the polarization field not only made the band diagram smoother but also
restricted electron overflow to the p-GaN layer as shown in simulations. These results indicate that
semi-polar InGaN-based LEDs can possess a high radiative recombination rate and low efficiency
droop at a high injection current.
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.