Microwave performance and structural characterization of MBE-grown AlGaN/GaN HEMTs on low dislocation density GaN substrates

ABSTRACTWe have developed a new method to prepare low-dislocation-density GaN by using periodically grooved substrates in a conventional MOVPE growth technique. This new approach was demonstrated for GaN grown on periodically grooved α-Al2O3(0001), 6H-SiC(0001)Si and Si(111) substrates. Dislocation densities were 2×107 cm−2 in low-dislocation-density area.

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STRUCTURAL CHARACTERIZATION OF CO-PRECIPITATED Cd1-xZnxS:Cu CRYSTALS

International Journal of Modern Physics B ◽

10.1142/s0217979202008099 ◽

2002 ◽

Vol 16 (03) ◽

pp. 481-496 ◽

Cited By ~ 4

Author(s):

ABDUL NAYEEM ◽

K. YADAIAH ◽

G. VAJRALINGAM ◽

P. MAHESH ◽

M. NAGABHOOSHANAM

Keyword(s):

Grain Size ◽

Dislocation Density ◽

Internal Stress ◽

Lattice Constant ◽

Structural Characterization ◽

Structural Parameters ◽

Size Variation ◽

Preferred Orientation ◽

Average Internal Stress

Structural characterization of Cd 1-x Zn x S : Cu solid solutions were carried out with 0≤x≤1. XRD studies have revealed that the compounds are polycrystalline in nature having either Hexagonal (wurtzite) or Cubic (Zincblende) structure irrespective of their composition. Also the compounds have shown the most preferred reflections due to the plane [101] of CdS(H) and [111] of ZnS(C) in addition to other prominent reflections. The various structural parameters such as lattice constant, average internal stress, micro strain, dislocaion density, grain size, and preferred orientation were correlated with the composition. The lattice constant decreased linearly with the increase in Zn concentration. The sign of internal stress indicated elongational and compressional natures corresponding to hexagonal and cubic phases of CdS respectively. The variation of micro strain appeared to be conjugate when compared to grain size variation, and the variation of dislocation density with the composition showed a higher dislocation density till x=0.4 and then decreased till x=0.8 and then increased. The degree of preferred orientation in mixed Cd 1-x Zn x S : Cu crystals as observed by the maximum peak intensity of CdS(H) and ZnS(C) reflection showed that the degree of preferred orientation remained almost constant till x=0.6 and then increased. The results were explained on the basis of different phases of the compound and the defects related to Zn atoms.

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Compositional and Structural Characterization of Heterostructure InGaN-Based Light-Emitting Diode by High Resolution X-Ray Diffraction

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.620.22 ◽

2012 ◽

Vol 620 ◽

pp. 22-27 ◽

Cited By ~ 1

Author(s):

Ahmad Hadi Ali ◽

Ahmad Shuhaimi ◽

Hassan Zainuriah ◽

Yushamdan Yusof

Keyword(s):

High Resolution ◽

Dislocation Density ◽

Structural Characterization ◽

Light Emitting Diode ◽

X Ray Diffraction ◽

Rocking Curve ◽

Light Emitting ◽

X Ray ◽

Multi Quantum Well

This paper focuses on the compositional and structural characterization of InGaN-based light-emitting diode (LED) using high resolution x-ray diffraction (HRXRD) system. The LED was epitaxially grown on Si (111) substrate that comprises of In0.11Ga0.89N multi-quantum-well (MQW) active layer. Phase analysis 2θ-scan proved the composition of GaN (0002) and (0004) at 34.63oand 72.98o, respectively. Rocking curveφ-scan showed six significant peaks of the hexagonal GaN structures with consistent angular gaps of ~60o. From x-ray rocking curve (XRC)ω-scan, screw and mix dislocation density is found as 2.85 × 109cm-2, while pure edge dislocation density is found as 2.23 × 1011cm-2.

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Growth Mechanism and Characterization of Low-Dislocation-Density AlGaN Single Crystals Grown on Periodically Grooved Substrates

phys stat sol (a) ◽

10.1002/1521-396x(200112)188:2<799::aid-pssa799>3.0.co;2-4 ◽

2001 ◽

Vol 188 (2) ◽

pp. 799-802 ◽

Cited By ~ 11

Author(s):

T. Detchprohm ◽

S. Sano ◽

S. Mochizuki ◽

S. Kamiyama ◽

H. Amano ◽

...

Keyword(s):

Dislocation Density ◽

Single Crystals ◽

Growth Mechanism ◽

Low Dislocation Density

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PERFORMANCE OF PSEUDOMORPHIC ULTRAVIOLET LEDs GROWN ON BULK ALUMINUM NITRIDE SUBSTRATES

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156411006787 ◽

2011 ◽

Vol 20 (03) ◽

pp. 497-504 ◽

Cited By ~ 1

Author(s):

SHAWN R. GIBB ◽

JAMES R. GRANDUSKY ◽

MARK MENDRICK ◽

LEO J. SCHOWALTER

Keyword(s):

Dislocation Density ◽

Published Data ◽

Epitaxial Layers ◽

Device Structure ◽

Low Dislocation Density ◽

High Aluminum Content ◽

Current Densities ◽

Pseudomorphic Growth ◽

High Aluminum

Low dislocation density pseudomorphic epitaxial layers of Al x Ga 1- x N have been grown on c -face AlN substrates prepared from high quality bulk crystals. As reported previously, pseudomorphic growth yields very low dislocation density layers with atomically smooth surfaces throughout the active region of a full LED device structure. An advantage of the low dislocation density is the ability to n -type dope the high aluminum content Al x Ga 1- x N (x ~ 70%) epitaxial layers required for UVLED devices to obtain sheet resistances less than 350 Ohm/square for 0.5 μm thick layers. Here, we report on the characterization of our pseudomorphic epitaxial AlGaN layers via cathodoluminescence (CL) and on-wafer and initial packaged level characterization of fully fabricated pseudomorphic ultraviolet LEDs (PUVLEDs) with an emission wavelength between 250 - 265 nm. An additional benefit of PUVLED devices is the ability to run these devices at high input powers and current densities. Further, the aforementioned low dislocation density of the epitaxial structure results in improved device performance over previously published data. Mean output powers of greater than 4 mW were obtained on-wafer prior to thinning and roughening while output powers as high as 45 mW were achieved for packaged devices.

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Microstructure Characterization of Hot Deformed Fe-32%Ni Alloy

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.230-232.154 ◽

2011 ◽

Vol 230-232 ◽

pp. 154-158 ◽

Cited By ~ 1

Author(s):

Bao Jun Han

Keyword(s):

Dislocation Density ◽

Dynamic Equilibrium ◽

Optical Microscope ◽

Electron Back Scatter Diffraction ◽

High Dislocation Density ◽

Hot Deformation Behavior ◽

Transmission Electron ◽

Low Dislocation Density ◽

Ni Alloy

Hot deformation behavior and microstructure evolution of Fe-32%Ni alloy were investigated when compressed at the temperature of 1000°C and a strain rate of 2×10-3s-1. The microstructures were analyzed using optical microscope (OM), electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that the generation and development of dynamic recrystallization (DRX) can obviously refine the grains of Fe-32Ni% alloy and the DRX reached dynamic equilibrium when the strain was high. According to the TEM observations, the DRX microstructure can be categorized into three kinds: grains with low dislocation density, which are DRX nucleations; grains with low dislocation density around the grain boundary and high dislocation density in its interior which means that grains with dislocation density gradient and which are DRX grains in growth; grains with high dislocation density, which are fully work-hardened DRX grains.

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New ultrastructural findings about Borrelia burgdorferi by cryofixation, negative staining, thin sectioning and scanning techniques

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100160467 ◽

1990 ◽

Vol 48 (3) ◽

pp. 582-583

Author(s):

S. F. Hayes ◽

M. D. Corwin ◽

T. G. Schwan ◽

D. W. Dorward ◽

W. Burgdorfer

Keyword(s):

Lyme Disease ◽

Borrelia Burgdorferi ◽

Structural Characterization ◽

Negative Staining ◽

Low Speed ◽

Thin Sectioning ◽

Ultrastructural Findings

Characterization of Borrelia burgdorferi strains by means of negative staining EM has become an integral part of many studies related to the biology of the Lyme disease organism. However, relying solely upon negative staining to compare new isolates with prototype B31 or other borreliae is often unsatisfactory. To obtain more satisfactory results, we have relied upon a correlative approach encompassing a variety EM techniques, i.e., scanning for topographical features and cryotomy, negative staining and thin sectioning to provide a more complete structural characterization of B. burgdorferi.For characterization, isolates of B. burgdorferi were cultured in BSK II media from which they were removed by low speed centrifugation. The sedimented borrelia were carefully resuspended in stabilizing buffer so as to preserve their features for scanning and negative staining. Alternatively, others were prepared for conventional thin sectioning and for cryotomy using modified procedures. For thin sectioning, the fixative described by Ito, et al.

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