Strain analysis of InGaN/GaN multi quantum well LED structures (original) (raw)
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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.
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
Five period InGaN/GaN MQW LED wafers were grown by low pressure MOCVD on an AlN buffer layer, which was deposited on a c-plane (0001)-faced sapphire substrate. The effect of growth conditions, such as the well growth time, growth temperatures, and indium flow rate on the properties of MQW structures were investigated by using high resolution X-ray diffraction and room temperature photoluminescence. By increasing growth temperature, the emission wavelengths showed a blue-shift while it red-shifted via an increase in the indium flow rate. The emission wavelength can be tuned by way of changing the well growth time of the samples.
Structural analysis of an InGaN/GaN based light emitting diode by X-ray diffraction
Journal of Materials Science-materials in Electronics, 2010
The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample.
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.
Investigation of structural, optical and morphological properties of InGaN/GaN structure
Applied Physics A, 2018
In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.
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.
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.
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.
Journal of Polytechnic, 2018
Structural properties of InGaN/GaN solar cells (SCs) grown by metal organic chemical vapor deposition (MOCVD) technique are investigated by high resolution X-ray diffraction (HR-XRD) method. It is noticed that a-and c-lattice parameters of the structures showed small differences according to examined (hkl) planes. Fault percentage of the a-and c-lattice parameters are also calculated. It is seen that fault percentage is smaller than %2 for all samples. Investigations have been made for three different samples. Differences in crystal quality caused by growth conditions are seen in all three samples. At the same time, properties such as crystal size, strain and stress are determined. During determination of stress, two different methods including elastic constants, Young module and Poisson ratio are used. Results gained from these two methods are compared with each other. Thermal expansion coefficients of InGaN are calculated for (002), (004), (006) and (121) planes for 100 o C temperature difference (300-400 o C). It is seen that peak positions gained from HR-XRD are nearly the same with the ones in database. All the results obtained from calculations are given in tables in the following sections of this article. It can be seen that all these results are in accordance with previous works done by different authors and with the real values.