Dislocation analysis in homoepitaxial GaInN/GaN light emitting diode growth (original) (raw)
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Physical Review B, 2010
The creation of symmetrical pairs of inclined dislocations was observed in the GaInN/GaN quantum wells ͑QWs͒ of c-axis grown green light-emitting diodes ͑LEDs͒ on low-defect density bulk GaN substrate, but not in green LEDs on sapphire substrate with high threading dislocation ͑TD͒ density. Pairs of dislocations start within 20 nm of the same QW and incline 18°-23°toward two opposite ͗1100͘ directions or in a 120°pattern. We propose that in the absence of TDs, partial strain relaxation of the QWs drives the defect formation by removal of lattice points between the two dislocation cores. In spite of those inclined dislocation pairs, the light output power of such green LEDs on GaN is about 25% higher than in LEDs of similar wavelength on sapphire.
physica status solidi (b), 2010
We report on the reduction of the threading edge dislocation density of Al 0.15 Ga 0.85 N buffer layers for efficient 350 nm light-emitting diodes (LEDs). Structures were grown by metalorganic vapor phase epitaxy (MOVPE) on (0001) sapphire substrates using three-dimensional (3D) facetted GaN nucleation islands. The flattening of the overgrowing AlGaN buffer layers could be controlled by choosing appropriate growth conditions resulting in smooth surfaces. High-resolution X-ray diffraction (HRXRD) v-scans show that a prolonged 3D growth phase leads to a narrowing of the asymmetric diffraction peaks and hence to an effective reduction of the density of edge-type threading dislocations. Photoluminescence (PL) and electroluminescence (EL) measurements show directly the beneficial effect of the improved crystal quality on the optical emission properties. The output power of LED structures grown on an optimized buffer was increased by a factor of 6 compared to structures grown on a two-dimensional (2D) low Al content AlGaN nucleation layer.
physica status solidi (c), 2004
In this work we demonstrate the quality of laser diodes fabricated on bulk GaN substrates. These substrates were obtained via high-temperature, high-pressure synthesis and are characterized by a dislocation density as low as 10 2 cm -2 . The epitaxial structure was deposited using a combination of MOVPE and MBE methods. Thanks to such a low and uniform density of dislocations it was possible to realize high power, pulsed current laser diodes with a total output power exceeding 2.5 W. Interestingly enough, the MBE growth method can produce very satisfying results once the growth is resumed on bulk GaN substrates. This contradicts the common believe concerning the poor applicability of the MBE method for the growth of nitride violet laser structures.
Structural Analysis in Low-V-defect Blue and Green GaInN/GaN Light Emitting Diodes
In this study, we characterized the structural defects in blue and green GaInN/GaN LEDs grown on c-plane bulk GaN and sapphire substrates. Low density large V-defects with diameters around 600 nm were found in the blue LEDs on bulk GaN. They were initiated by edge-type threading dislocations (TDs) around the homoepitaxial growth interface. On the other hand, a high density 7×10 9 cm-2 of smaller V-defects with sidewalls on } 01 1 1 { facets was observed in the active region of green LEDs on sapphire. Their diameter ranges from 150 to 200 nm. Misfit dislocations (MDs) generated in the quantum wells are found to initiate these V-defects. With optimizing the epitaxial growth conditions, the generation of MDs and their smaller V-defects was largely suppressed. As a result, the light output power improved by one order of magnitude. For green LEDs on bulk GaN, another unique type of defect was found in the active region: an inclined dislocation pair (IDP). In it a pair of dislocations propagate at a tilt angle of 18 to 23º from the [0001] growth direction towards > < 00 1 1. This defect seems to be a path of strain relief in the high indium composition quantum wells.
Design and fabrication of enhanced lateral growth for dislocation reduction in GaN using nanodashes
Journal of Crystal Growth, 2017
The semiconductor gallium nitride is the material at the centre of energy-efficient solid-state lighting and is becoming increasingly important in high-power and high-frequency electronics. Reducing the dislocation density of gallium nitride planar layers is important for improving the performance and reliability of devices, such as light-emitting diodes and high-electron-mobility transistors. The patterning of selective growth masks is one technique for forcing a three-dimensional growth mode in order to control the propagation of threading defects to the active device layers. The morphology of the three-dimensional growth front is determined by the relative growth rates of the different facets that are formed, and for GaN is typically limited by the slow-growing {1 À1 0 1} facets. We demonstrate how the introduction of nanodash growth windows can be oriented in an array to preserve fast-growing {1 1 À2 2} facets at the early stage of growth to accelerate coalescence of three-dimensional structures into a continuous GaN layer. Cathodoluminescence and Electron Channelling Contrast Imaging methods, both used to measure the threading dislocation density, reveal that the dislocations are organised and form a distinctive pattern according to the underlying mask. By optimising the arrangement of nanodashes and the nanodash density, the threading dislocation density of GaN on sapphire epilayers can be reduced significantly from 10 9 cm À2 to 3.0 Â 10 7 cm À2. Raman spectroscopy, used to monitor the strain in the overgrown GaN epilayers, shows that the position of the GaN E 2 H phonon mode peak was reduced as the dash density increases for a sample grown via pendeo-epitaxy whilst no obvious change was recorded for a sample grown via more conventional epitaxial lateral overgrowth. These results show how growth mask design can be used to circumvent limitations imposed by the growth dynamics. Moreover, they have revealed a greater understanding of the influence of the growth process on the dislocation density which will lead to higher performing electronic and optoelectronic devices as a result of the lower dislocation densities achieved.
Low-dislocation-density GaN from a single growth on a textured substrate
Applied Physics Letters, 2000
The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates *m is typically greater than 109/cm2. Such high dislocation densities degrade both the electronic so and photonic properties of the material. The density of dislocations can be decreased b~~@ orders of magnitude using cantilever epitaxy (CE), which employs prepattemed sapphire substrates to provide reduced-dmension mesa regions for nucleation and etched trenches ($)42 between them for suspended lateral growth of Gall or AIGaN. The substrate k prepattemed d~w ith narrow lines and etched to a depth that permits coalescence of laterally growing III-N~@ nucleated on the mesa stiaces before vertical growth fills the etched trench. Low a dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.
Influence of dislocation density on photoluminescence intensity of GaN
Journal of Crystal Growth, 2005
The influence of dislocation density on photoluminescence intensity is investigated experimentally and compared to a model. GaN samples were grown by molecular beam epitaxy and metal-organic chemical vapour deposition. Different growth parameters and thicknesses of the layers resulted in different dislocation densities. The threading dislocation density, measured by atomic force microscopy, scanning electron microscopy and X-ray diffraction, covered a range from 5 Â 10 8 to 3 Â 10 10 cm À2. Carrier concentration was measured by capacitance-voltage-, and Hall effect measurements and photoluminescence at 2 K was recorded. A model which accounts for the photoluminescence intensity as a function of dislocation density and carrier concentration in GaN is developed. The model shows good agreement with experimental results for typical GaN dislocation densities, 5 Â 10 8-1 Â 10 10 cm À2 , and carrier concentrations 4 Â 10 16-1 Â 10 18 cm À3 .
MRS Proceedings, 2005
An alternative scheme to the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been previously introduced that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. Here, the effects of N+ ion implantation of AlN/Si (111) substrate on the structural and optical properties of the overgrown GaN epilayers have been investigated. Temperature dependent photoluminescence has been used to investigate the impact of the implantation conditions (energy and dose) on optical and structural quality of the GaN overgrown layers. A correlation between PL and high resolution x-ray diffraction (XRD) of the overgrown GaN layers show that the lowest FWHM of bandedge, the highest bandedge to deep defect blue luminescence band ratio, and the lowest symmetric rocking curve FWHM are achieved for the optimized implantation conditions. This correlates well with the results of etch pit de...