High-Efficiency GaN/AlxGa1 - xN Multi-Quantum-Well Light Emitter Grown on Low-Dislocation Density AlxGa1 - xN (original) (raw)
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Low-dislocation-density GaN and AlxGa1−xN (x⩽0.13) grown on grooved substrates
Journal of Crystal Growth, 2002
We proposed the heteroepitaxial lateral overgrowth technique using grooved sapphire (0 0 0 1) and ð1 1 % 2 0Þ SiC(0 0 0 1) Si and Si(1 1 1) substrates to prepare Al x Ga 1Àx N single crystalline films with low dislocation density. Straight grooves of these substrates were aligned parallel to the /1 % 10 0S or /1 1 % 2 0S direction of Al x Ga 1Àx N. In this technique, neither a selective growth mask nor patterned GaN single crystal film was used. Dislocation densities lower than about 10 6 cm À2 were ascertained via plan-view TEM. This technique is promising for growing low-dislocationdensity nitride-based semiconductors.
High temperature AlN intermediate layer in GaN grown by molecular beam epitaxy
Journal of Crystal Growth, 2000
High-temperature AlN intermediate layers with di!erent thicknesses were deposited during the growth of wurtzite GaN on (0 0 0 1) sapphire substrates by plasma-assisted molecular beam epitaxy. When using a 3.5 nm AlN intermediate layer temperature-dependent Van-der-Pauw Hall measurements revealed a mobility enhancement by a factor of 2.5 at room temperature and by a factor of 32 at 30 K. Transmission electron microscopy con"rmed that the better material quality was due to a reduction of dislocation density by about one order of magnitude. Photoluminescence measurements indicate a decrease of full-width at half-maximum of the main emission peak for GaN samples with AlN intermediate layer.
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...
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.
Growth of Crack-Free Thick AlGaN Layer and its Application to GaN-Based Laser Diode
MRS Proceedings, 1999
In the field of group-III nitrides, hetero-epitaxial growth has been one of the most important key technologies. A thick layer of AlGaN alloy with higher AlN molar fraction is difficult to grow on sapphire substrate, because the alloy layer is easily cracked. It is thought that one cause of generating cracks is a large lattice mismatch between an AlGaN and a GaN, when AlGaN is grown on the underlying GaN layer. We have achieved crack-free Al 0.07 Ga 0.93 N layer with the thickness of more than 1µm using underlying Al 0.05 Ga 0.95 N layer. The underlying Al 0.05 Ga 0.95 N layer was grown directly on sapphire by using the lowtemperature-deposited buffer layer (LT-buffer layer). Since a lattice mismatch between the underlying Al 0.05 Ga 0.95 N layer and upper Al 0.07 Ga 0.93 N layer is relatively small, the generation of cracks is thought to be suppressed. This technology is applied to a GaN-based laser diode structure, in which thick n-Al 0.07 Ga 0.93 N cladding layer grown on the Al 0.05 Ga 0.95 N layer, improves optical confinement and single-robe far field pattern in vertical direction.
Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire
MRS Proceedings, 2000
Layers of Al x Ga 1Ϫx N, with 0рxр1, were grown on Si͑111͒ substrates by gas source molecular beam epitaxy with ammonia. We show that the initial formation of the SiN -Al interlayer between the Si substrate and the AlN layer, at a growth temperature of 1130-1190 K, results in very rapid transition to two-dimensional growth mode of AlN. The transition is essential for subsequent growth of high quality GaN, Al x Ga 1Ϫx N, and AlGaN/GaN superlattices. The undoped GaN layers have a background electron concentration of (2-3)ϫ10 16 cm Ϫ3 and mobility up to ͑800Ϯ100͒ cm 2 /V s, for film thickness ϳ2 m. The lowest electron concentration in Al x Ga 1Ϫx N, with 0.2ϽxϽ0.6, was ϳ(2-3)ϫ10 16 cm Ϫ3 for 0.5-0.7-m-thick film. Cathodoluminescence and optical reflectance spectroscopy were used to study optical properties of these Al x Ga 1Ϫx N layers. We found that the band gap dependence on composition can be described as E g (x)ϭ3.42ϩ1.21xϩ1.5x 2. p-n junctions have been formed on crack-free layers of GaN with the use of Mg dopant. Light emitting diodes with peak emission wavelength at 3.23 eV have been demonstrated.
Growth and Characterization of AlxGa1-xN on GaN/Al2O3
16th International Workshop on Physics of Semiconductor Devices, 2012
AlGaN is a promising material to develop UVLEDs and HEMT devices due to the direct wide-band gap material. In the present investigation, AlxGa 1-xN alloys were grown on c-plane sapphire substrate by MOCVD. Al content x was varied in the composition range 0≤x≤0.6. The thickness and Al composition of the AlGaN was determined by HRXRD. The growth rate decreases on increasing the composition of Al. The critical thickness of pseudomorphic AlGaN layer decreases on increasing the composition. Thick layers resulted in cracks and it is important to grow thick layers with high aluminum content free from crack for deep UV LEDs.
Reduction of threading dislocation density in GaN grown on strain relaxed nanoporous GaN template
2007
Although suitable for the reduction of the threading dislocation density in GaN layers the widely used two-step MOCVD method does not work as efficiently for AlGaN. This is due to slow surface diffusion of the Al species. In the present paper, the previously reported in situ multistep method for MOCVD growth of high-quality GaN films is adopted for the growth of Al 0.12 Ga 0.88 N films on c-plane sapphire. The developed method for AlGaN growth is virtually GaN free in the sense that no continuous film of GaN is needed near the substrate interface. Crack-free layers of Al 0.12 Ga 0.88 N with a thickness of about 2 mm are grown by the method. A sparse distribution of 3D GaN nucleation islands and stimulation of threading dislocation reactions enable a reduction of the threading dislocation density down to 5 Â 10 8 cm À2 in the Al 0.12 Ga 0.88 N films. The threading dislocation density is evaluated by etch-pit density measurements. Highresolution X-ray diffraction and transmission electron microscopy are used to study the crystallinity of the Al 0.12 Ga 0.88 N layers. Reflectometry is utilized to analyze film growth in situ. The surface morphology of GaN nucleation layers and Al 0.12 Ga 0.88 N epilayers is characterized by atomic force microscopy. r
Journal of Physics: Conference Series, 2016
We report on successful growth by plasma-assisted molecular beam epitaxy on a Si(111) substrate crack-free GaN/AlN buffer layers with a thickness more than 1 μm. The layers fabricated at relatively low growth temperature of 780°C have at room temperature the residual compressive stress of-97 MPa. Intrinsic stress evolution during the GaN growth was monitored in situ with a multi-beam optical system. Strong dependence of a stress relaxation ratio in the growing layer vs growth temperature was observed. The best-quality crack-free layers with TDs density of ~10 9 cm-2 and roughly zero bowing were obtained in the sample with sharp 2D-GaN/2D-AlN interface.