High efficiency InGaN/GaN light emitting diodes with asymmetric triangular multiple quantum wells (original) (raw)
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Materials Science in Semiconductor Processing, 2021
This work presents an interesting observation on a possible growth regime transition from diffusion-limited to desorption-limited at Multi-Quantum Well (MQW) growth structure. In common practices, this transition is normally observed by increasing the growth temperature. However, in this work, this phenomenon is noticed by increasing the V/III ratio during the Indium Gallium Nitride/Gallium Nitride (InGaN/GaN) MQW growth process. By increasing the nitrogen (N)-precursors, the V/III of MQW growth structure was varied at three different ratios of 5109, 6387 and 7664 respectively. The X-ray Diffraction (XRD) peaks measured on these three devices reveals the highest Indium (In) incorporation of ~11.2% is obtained at 5109 ratios followed by 6387 ratios with ~5.0% and ~0.0% incorporation for 7664 ratios. Additionally, the EDX mapping also discloses the presence of In element on the p-GaN surface and it reduces significantly with the increase of the MQW V/III ratios. This trend implies the MQW growth process was occurred under diffusion-limited regime, which also affects the p-GaN upper layer. However, XRD results shows that the increment of MQW V/III ratios depreciates the MQW thicknesses, which manifests that the growth condition changed to metal-limited or N-rich regime, where the important reactants start to desorb from the sample. This leads to the low growth rate of InGaN/GaN layer and degrades the devices performance. The blue shift of InGaN peaks in photoluminescence spectra has support the notion of In reduction at high MQW V/III ratios. At 20 mA, the devices of 5109 and 6387 ratios with a forward voltage of 3.57 V and 3.95 V produce electroluminescence peak at 443.74 nm and 487.45 nm, respectively. Despite the 5109 sample exhibits the highest In percentage, green speckles were produced at low optical threshold voltage due to the proliferation of localization states induced by the In clusters. The device also experiences the higher reverse current leakage compared to 6387 device due to higher threading dislocation density.
IEEE Journal of Selected Topics in Quantum Electronics, 2009
Efficiency droop behavior of InGaN/GaN multiplequantum-well LEDs with various well thicknesses is discussed. It is demonstrated that LED samples with thinner well structures possess higher external quantum efficiencies with stronger droop behaviors. The efficiency droop behavior is contributed by dislocation recombination, Auger recombination in an active region, and carrier overflow out of an active region. Simulation results suggest that at the current density region of 10-100 A/cm 2 , Auger recombination is a dominant mechanism for efficiency droop behavior, while at high current density region of 100-200 A/cm 2 , carrier overflow starts to be the major mechanism for the change of efficiency droop behaviors.
Journal of Physics D-applied Physics, 2010
We investigated InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with trapezoidal wells to improve the efficiency droop. MQW LEDs with trapezoidal wells showed a lower operating voltage and an improved efficiency droop with a low crossover current density of 5 A cm-2, which was a significant improvement over conventional LEDs that use rectangular wells. The external quantum efficiency was increased by 20% at a current density of 70 A cm-2. The improvement in efficiency droop of the MQWs with trapezoidal wells can be attributed to an increased internal quantum efficiency due to the enhanced overlap of the electron and hole wave functions at high current densities.
Applied Physics Letters, 2010
We have studied the characteristics of efficiency droop in GaN-based light emitting diodes ͑LEDs͒ with different kinds of insertion layers ͑ILs͒ between the multiple quantum wells ͑MQWs͒ layer and n-GaN layer. By using low-temperature ͑LT͒ ͑780°C͒ 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 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 5.3ϫ 10 8 cm −2 , in its MQWs region is much higher than that value of 2.9ϫ 10 8 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.
Improved electroluminescence on nonpolarm -plane InGaN/GaN quantum wells LEDs
physica status solidi (RRL) – Rapid Research Letters, 2007
The remarkable progress in III-nitride semiconductors has enabled widespread development of high power and high efficiency optoelectronic devices. Due to its stability during epitaxial growth, the polar c-axis is the common orientation for the deposition of III-N film and heterostructures even though the performance of these devices suffers from strong polarization-related electric fields along the growth-direction. These polarization fields result in a separation between electron and hole wave functions as well as a reduction in radiative recombination rate in active regions . To avoid this situation, there have been several reports of light emitting diodes (LEDs) grown and fabricated on nonpolar aand m-plane gallium nitride (GaN) on r-plane sapphire and m-plane SiC substrates using metalorganic chemical vapor deposition (MOCVD) [5], hydride vapor phase epitaxy (HVPE) [6], or molecular beam epitaxy (MBE) . However, heteroepitaxy, which uses foreign substrates, causes a high density of extended defects [9] such as threading dislocations (TDs) and basal stacking faults (SFs). These defects can be sources of non-radiative recombination centers that reduce the internal quantum efficiency and additionally act as charge scattering centers that decrease the carrier mobil-
Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth
Applied Physics Letters, 1999
The emission mechanisms of bulk GaN and InGaN quantum wells ͑QWs͒ were studied by comparing their optical properties as a function of threading dislocation ͑TD͒ density, which was controlled by lateral epitaxial overgrowth. Slightly improved excitonic photoluminescence ͑PL͒ intensity was recognized by reducing TD density from 10 10 cm Ϫ2 to less than 10 6 cm Ϫ2 . However, the major PL decay time was independent of the TD density, but was rather sensitive to the interface quality or material purity. These results suggest that TDs simply reduce the net volume of light-emitting area. This effect is less pronounced in InGaN QWs where carriers are effectively localized at certain quantum disk size potential minima to form quantized excitons before being trapped in nonradiative pathways, resulting in a slow decay time. The absence of any change in the optical properties due to reduction of TD density suggested that the effective band gap fluctuation in InGaN QWs is not related to TDs.