Effect of InGaN quantum dot size on the recombination process in light-emitting diodes (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.
Microscopic, electrical and optical studies on InGaN/GaN quantum wells based LED devices
We report here on the micro structural, electronic and optical properties of a GaN-based InGaN/GaN MQW LED grown by the MOVPE method. The present study shows that the threading dislocations present in these LED structures are terminated as V pits at the surface and have an impact on the electrical and optical activity of these devices. It has been pointed that these dislocations were of edge, screw and mixed types. EBIC maps suggest that the electrically active defects are screw and mixed dislocations and behave as nonradiative recombinant centres.
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.
Optics Express, 2014
In this work, InGaN/GaN light-emitting diodes (LEDs) possessing varied quantum well (QW) numbers were systematically investigated both numerically and experimentally. The numerical computations show that with the increased QW number, a reduced electron leakage can be achieved and hence the efficiency droop can be reduced when a constant Shockley-Read-Hall (SRH) nonradiative recombination lifetime is used for all the samples. However, the experimental results indicate that, though the efficiency droop is suppressed, the LED optical power is first improved and then degraded with the increasing QW number. The analysis of the measured external quantum efficiency (EQE) with the increasing current revealed that an increasingly dominant SRH nonradiative recombination is induced with more epitaxial QWs, which can be related to the defect generation due to the strain relaxation, especially when the effective thickness exceeds the critical thickness. These observations were further supported by the carrier lifetime measurement using a pico-second time-resolved photoluminescence (TRPL) system, which allowed for a revised numerical modeling with the different SRH lifetimes considered. This work provides useful guidelines on choosing the critical QW number when designing LED structures.
High efficiency InGaN/GaN light emitting diodes with asymmetric triangular multiple quantum wells
Applied Physics Letters, 2014
In this study, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, LEDs incorporated with asymmetric triangular MQWs with gallium face-oriented inclination band profiles exhibited a 60.0% external quantum efficiency at 20 mA and a 27.0% efficiency droop at 100 mA (corresponding to a current density of 69 A/cm 2 ), which accounted for an 11.7% efficiency improvement and a 31.1% droop reduction compared with symmetric square quantum well structure LEDs. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4867023\]
400-nm InGaN-GaN and InGaN-AlGaN multiquantum well light-emitting diodes
IEEE Journal of Selected Topics in Quantum Electronics, 2002
Rcenctly, tremendous progress has been achieved in GaN-based blue and green lightemitting diodes (LEDs). These blue/green LEDs have already been extensively used in fullcolor displays and high-efficient light sources for traffic light lamps. Although these blue/ green LEDs are already commercially available, it is still difficult to achieve LEDs emitting at even shorter wavelength regions, such as ultraviolet (UV) region. Short wavelength emitters are of interest for various fluorescence-based chemical sensing applications, high efficiency lighting, flame detection, and possibly optical storage applications. Conventional nitridebased multiquantum well (MQW) LEDs use InGaN as the material for well layers and GaN as the material for barrier layers. To achieve a short wavelength emitter, one needs to reduce the indium composition in the well layers so as to increase its bandgap energy. However, a reduction in indium composition in the well layers will result in a small bandgap discontinuity at the well/barrier interfaces. Thus, the quantum well depth in the MQW active region will become smaller and the carrier confinement effect will be reduced. As a result, severe carrier leakage problem might occur in the short wavelength InGaN-GaN MQW LEDs. One possible way to solve this problem is to use AlGaN or AlGaInN as the barrier layers instead of GaN. The quaternary AlGaInN permits an extra degree of freedom by allowing independent control of the bandgap and lattice constant. Thus, the use of quaternary AlGaInN for barrier layers could potentially offer better carrier confinement while minimizing lattice mismatch issues. However, it is much more difficult to grow high-quality AlGaInN than AlGaN. Since the bandgap energy of AlGaN is also larger than that of GaN, InGaN-AlGaN MQW should still be able to provide a better carrier confinement, as compared to InGaN-GaN MQW. Also, since the lattice constant of AlGaN is smaller while the lattice constant of InGaN is larger than that of GaN base layer, it is possible to achieve a strain compensated InGaN-AlGaN MQW on GaN with proper composition ratios in InGaN and AlGaN layers. As a result, we could increase the effective MQW critical thickness, and thus reduce the probability of relaxation occurred within the MQW active region. In this study, InGaN-GaN LED and InGaN-AlGaN LED will both be fabricated. The optical and electrical properties of these LEDs will be reported.
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-
Crystals, 2021
InGaN quantum dots (QDs) are promising candidates for GaN-based all-visible optoelectronic devices such as micro light-emitting diode and laser. In this study, self-assembled InGaN/GaN multi-quantum dots (MQDs) have been grown by plasma-assisted molecular beam epitaxy on c-plane GaN-on-sapphire template. A high density of over 3.8 × 1010 cm−2 is achieved and InGaN QDs exhibit a relatively uniform size distribution and good dispersity. Strong localization effect in as-grown InGaN QDs has been evidenced by temperature-dependent photoluminescence (PL). The variation of peak energy is as small as 35 meV with increasing temperature from 10 K to 300 K, implying excellent temperature stability of emission wavelength for InGaN MQDs. Moreover, the radiative and nonradiative recombination times were calculated by time-resolved PL (TRPL) measurements, and the temperature dependence of PL decay times reveal that radiative recombination dominates the recombination process due to the low dislocat...
Nano-structures and luminescence mechanisms of InGaN/GaN multiple quantum well light emitting diodes
The International Conference on Electrical Engineering, 2008
A series of InGaN/GaN MQW LEDs were prepared by low pressure metalorganic chemical vapor deposition (MOCVD) and studied on the nano-structural features correlated with optical properties, and luminescence emission mechanisms by analytical techniques of photoluminescence (PL), PL excitation (PLE), time resolved PL (TRPL), high-resolution (HR) X-ray diffraction (XRD) and HR transmission electron microscopy (TEM). They have shown the excellent optical and structural properties, evidenced by HRXRD, HRTEM and optical measurements. The quantum dot like structure features, unique T-behaviors of PL spectra, quantum confined Stokes effect, TRPL exploration with the variation of detecting energy and temperature and modeling analyses are studied and discussed.