Strain variation in p-GaN by different spacer layers in the light emitting diodes and their microstructural and emission behaviors (original) (raw)
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Microstructural defect properties of InGaN/GaN blue light emitting diode structures
Journal of Materials Science: Materials in Electronics, 2014
In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.
Journal of Applied Physics, 2020
In this work, InGaN/GaN Multi-Quantum Wells (MQWs) with strain compensating AlGaN interlayers grown by metalorganic vapour phase epitaxy have been investigated by high resolution X-ray diffraction, transmission electron microscopy and photoluminescence (PL). For different AlGaN strain compensating layer thicknesses varying from 0 to 10.6 nm, a detailed X-ray diffraction analysis shows that the MQW stack become completely strained on GaN along a and c. The compensation is full from an AlGaN layer thickness of 5.2 nm, and this does not change up to the largest one that has been investigated. In this instance, the AlGaN was grown at the same temperature as the GaN barrier, on top of a protective 3 nm GaN. It is found that the crystalline quality of the system is progressively degraded when the thickness of the AlGaN interlayer is increased through strain concentrated domains which randomly form inside the 3 nm GaN low temperature layer. These domains systematically contribute to a loca...
Journal of Applied Physics, 2004
GaN template layer strain effects were investigated on the growth of InGaN/GaN LED devices. Seven period InGaN/GaN multiple quantum well structures were deposited on 5µm and 15µm GaN template layers. It was found that the electroluminescence emission of the 15µm device was red-shifted by approximately 132meV. Triple-axis X-Ray Diffraction and Cross-Sectional Transmission Electron Microscopy show that the 15µm templay layer device was virtually unstrained while the 5µm layer experienced tensile strain. Dynamic Secondary Ion Mass Spectrometry depth profiles show that the 15µm template layer device had an average indium concentration of 11% higher than that of the 5µm template layer device even though the structures were deposited during the same growth run. It was also found that the 15µm layer device had a higher growth rate than the 5µm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers.
Nano/Micro Engineered and Molecular Systems, 2009
In this paper, we studied a method to reduce the compressive strain in the InGaN/GaN multiple quantum well (MQW) structures by inserting a strain relief layer between n-GaN and MQWs. The improvements in the interface quality and the optical properties were investigated by photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) analysis. The samples showed S-shaped emission energy peak and stronger
Strain analysis of InGaN/GaN multi quantum well LED structures
Crystal Research and Technology, 2012
Five period InGaN/GaN multi quantum well (MQW) light emitting diode (LED) structures were grown by a metalorganic chemical vapor deposition (MOCVD) system on c-plane sapphire. The structural characteristics as a strain-stress analysis of hexagonal epilayers MQWs were determined by using nondestructive high resolution x-ray diffraction (HRXRD) in detail. The strain/stress analysis in AlN, GaN, and InGaN thin films with a variation of the In molar fraction in the InGaN well layers was conducted based on the precise measurement of the lattice parameters. The a-and c-lattice parameters of the structures were calculated from the peak positions obtained by rocking the theta axis at the vicinity of the symmetric and asymmetric plane reflection angles, followed by the in-plane and out-of-plane strains. The biaxial and hydrostatic components of the strain were extracted from the obtained a-and c-direction strains values.
InGaN stress compensation layers in InGaN/GaN blue LEDs with step graded electron injectors
Superlattices and Microstructures, 2018
We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well (MQW) structures with stepgraded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW region and as a result improves epitaxial quality that can be observed by 15-fold decrease of V-pit density. We observed more uniform distribution of In between quantum wells in MQW region from results of electro-and photoluminescence measurement. These structural improvements lead to increasing of radiant intensity by a factor of 1.7e2.0 and enhancement of LED efficiency by 40%.
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.
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.
The management of stress in MOCVD-grown InGaN/GaN LED multilayer structures on Si(1 1 1) substrates
Semiconductor Science and Technology, 2013
The tensile stress in light-emitting diode (LED)-on-Si(1 1 1) multilayer structures must be reduced so that it does not compromise the multiple quantum well emission wavelength uniformity and structural stability. In this paper it is shown for non-optimized LED structures grown on Si(1 1 1) substrates that both emission wavelength uniformity and structural stability can be achieved within the same growth process. In order to gain a deeper understanding of the stress distribution within such a structure, cross-sectional Raman and photo-luminescence spectroscopy techniques were developed. It is observed that for a Si:GaN layer grown on a low-temperature (LT) AlN intermediate layer there is a decrease in compressive stress with increasing Si:GaN layer thickness during MOCVD growth which leads to a high level of tensile stress in the upper part of the layer. This may lead to the development of cracks during cooling to room temperature. Such a phenomenon may be associated with annihilation of defects such as dislocations. Therefore, a reduction of dislocation intensity should take place at the early stage of GaN growth on an AlN or AlGaN layer in order to reduce a build up of tensile stress with thickness. Furthermore, it is also shown that a prolonged three dimensional GaN island growth on a LT AlN interlayer for the reduction of dislocations may result in a reduction in the compressive stress in the resulting GaN layer.
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.