Photoluminescence Study of Chloride Vpe-Grown Gan

1996 ◽  
Vol 421 ◽  
Author(s):  
Tetsuzo Ueda ◽  
Masaaki Yuri ◽  
Heon Lee ◽  
James S. Harris ◽  
Takaaki Baba
Keyword(s):  
Growth Temperature ◽  
Narrow Range ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Growth Conditions ◽  
Deep Acceptor ◽  
Flat Surfaces ◽  
Donor Acceptor ◽  
Dimensional Growth ◽  
Source Materials

AbstractWe have examined the effect of growth conditions on photoluminescence (PL) characteristics of chloride VPE-grown GaN films. Undoped GaN films are grown on sapphire by a newly developed chloride VPE system which utilizes GaCl3 and NH3 as source materials.We find that the spectra depend strongly on the growth temperatures and the corresponding surface morphology. Peaks from excitons and donor-acceptor pairs (D-A pair) recombination are observed for the films with terrace-like flat surfaces grown at between 950°C and 1000°C. A peak due to exciton bound to neutral donors is observed for a growth temperature of 975°C where the acceptor-related peaks are not seen. Decreasing the growth temperature below 950°C causes rough surfaces due to three-dimensional growth, whereas increasing the growth temperature above 1000°C causes cracks or partial pealing off of the film. The films with rough surfaces or crystal failures show broad emission from deep acceptor levels. As a result, residual acceptors are eliminated in the very narrow range of the growth temperature around 975°C. It is also noted that an increase of the V/III ratio during the growth makes the line width of the band-edge peak narrower. The PL results show that a growth temperature around 975°C and high V/III ratio are essential to obtain better crystal quality and reduced concentration of residual acceptors.

Damping in Lap Joints Due to Partial and Full Micro-Slip Using a Three Dimensional Elastic Contact of Rough Surfaces

2008 ◽  
Author(s):  
K. Farhang ◽  
A. Sepehri ◽  
D. Segalman ◽  
M. Starr
Keyword(s):  
Rough Surfaces ◽  
Tangential Force ◽  
Three Dimensional ◽  
Elastic Interaction ◽  
Lap Joints ◽  
Joint Interface ◽  
Flat Surfaces ◽  
Mechanical Joints ◽  
Statistical Sense ◽  
Scale Roughness

Energy dissipation in mechanical joints occurs as a result of micro-slip motion between contacting rough surfaces. An account of this phenomenon is especially challenging due to the vast differences in the length and time scale differences between the macro-mechanical structure and the micron-scale events at the joint interface. This paper considers the contact between two nominally flat surfaces containing micron-scale roughness. The rough surface interaction is viewed as a multi-sphere elastic interaction subject to a periodic tangential force. It combines the Mindlin’s formulation [1, 2] for the elastic interaction of two spheres with the Greenwood and Williamson’s [3] statistical approach for the contact of two nominally flat rough surfaces so as to develop a model for multi-sphere problem in which sphere radii, contact load and the number of spheres in contact can only be known in a statistical sense and not deterministically.

Photoluminescence in wurtzite GaN containing carbon

2005 ◽  
Vol 892 ◽  
Author(s):  
Michael A. Reshchikov ◽  
Random H. Patillo ◽  
Kathleen C. Travis
Keyword(s):  
Chemical Vapor ◽  
Growth Conditions ◽  
Shallow Donor ◽  
Clear Correlation ◽  
Acceptor Pair ◽  
Deep Acceptor ◽  
Shallow Acceptor ◽  
Low Intensity ◽  
Sapphire Substrates ◽  
Donor Acceptor

AbstractWe studied photoluminescence (PL) from a set of GaN layers grown on sapphire substrates by metalorganic chemical vapor deposition with the concentration of carbon varied by the growth conditions. One of the remarkable features in these samples is the extremely low intensity of the shallow donor-acceptor pair band. Analysis of the PL data gives the shallow acceptor concentration of less than 1014 cm-3 in most of the C-doped GaN layers. This result shows that C does not form a shallow acceptor, CN, in appreciable concentrations in wurtzite GaN. As for the YL band, there is no clear correlation between its intensity and the degree of C-doping. The question of identification of the deep acceptor responsible for the YL band in undoped and C-doped GaN still remains to be solved.

Surface nucleated half-loops in strained epilayers

1990 ◽  
Vol 48 (4) ◽  
pp. 560-561
Author(s):  
Eric P. Kvam
Keyword(s):  
Growth Temperature ◽  
Critical Thickness ◽  
Three Dimensional ◽  
Mechanical Damage ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Dislocation Type ◽  
Dimensional Growth ◽  
Edge Dislocations

Mismatched epilayers, grown beyond some critical thickness, have commonly been observed to have arrays of misfit-relieving dislocations at the heterointerface. In diamond or sphalerite structures, these arrays are orthogonal <110> networks of long 60° type dislocations, which are glissile and have inclined Burgers vectors. Up to the point at which growth becomes three-dimensional (about 2% mismatch in the (In,Ga)As/GaAs system), internal defects act as the sources for the misfit dislocations. Examples of such sources include pre-existing threading dislocations, internal loops, precipitates, and mechanical damage.In higher mismatch two-dimensional growth, such as can be produced in the GeSi/Si(001) system, the density of epithreading dislocations suddenly increases as the length of interfacial misfit dislocations falls. Almost simultaneously, the misfit dislocation type changes from 60° to edge. While in-situ hot stage experiments have shown that 60° type dislocations become mobile at about the growth temperature of the epilayer, and have observable velocities from this temperature on up, our observations of edge dislocations in the same system have shown that velocities for edge dislocations are essentially nil (measurable limit <lnm/s) even at 750°C, some 200°C above the growth temperature.

Hormonal modulation of ishikawa cells during three-dimensional growth in vitro☆

1998 ◽  
Vol 5 (4) ◽  
pp. 217-223 ◽  
Author(s):  
D PINELLI ◽  
J DRAKE ◽  
M WILLIAMS ◽  
D CAVANAGH ◽  
J BECKER
Keyword(s):  
Three Dimensional ◽  
Ishikawa Cells ◽  
Hormonal Modulation ◽  
Dimensional Growth

A New Deep Acceptor in Epitaxial Cubic SiC

1989 ◽  
Vol 162 ◽  
Author(s):  
J. A. Freitas ◽  
S. G. Bishop
Keyword(s):  
Thin Films ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Excitation Intensity ◽  
Acceptor Pair ◽  
Deep Acceptor ◽  
Intensity Dependence ◽  
Pl Spectra ◽  
Donor Acceptor ◽  
Donor Acceptor Pair

ABSTRACTThe temperature and excitation intensity dependence of photoluminescence (PL) spectra have been studied in thin films of SiC grown by chemical vapor deposition on Si (100) substrates. The low power PL spectra from all samples exhibited a donor-acceptor pair PL band which involves a previously undetected deep acceptor whose binding energy is approximately 470 meV. This deep acceptor is found in every sample studied independent of growth reactor, suggesting the possibility that this background acceptor is at least partially responsible for the high compensation observed in Hall effect studies of undoped films of cubic SiC.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

Study on the Surface Quality of Al2O3 Nano-Films by Ion Beam Sputtering Deposition

2011 ◽  
Vol 148-149 ◽  
pp. 54-57
Author(s):  
Xiao Ping Lin ◽  
Yun Dong ◽  
Lian Wei Yang
Keyword(s):  
Surface Quality ◽  
Ion Beam ◽  
Three Dimensional ◽  
Ion Beam Sputtering ◽  
Sputtering Deposition ◽  
Atomic Force ◽  
Beam Sputtering ◽  
Dimensional Growth ◽  
Different Thickness

The Al2O3 nano-films of different thicknesses (1~100nm) were successfully deposited on the monocrystalline Si surface by using ion beam sputtering deposition. The surface topography and the component of nano-films with different thickness were analyzed. The quality of the surface of nano-films was systematically studied. When the films’ thickness increase, the studies by atomic force microscope (AFM), X-ray photoelectron spectrum（XPS） show that the gathering grain continually grows up and transits from acerose cellula by two-dimensional growth to globularity by three-dimensional growth. The elements O, Al and Si were found on the surface of Al2O3 nano-films. With the thickness of the films increasing, the content of Al gradually increases and the intensity peak of Si wears off, the surface quality of the deposited films is ceaselessly improved

Strain in 3C–SiC Heteroepitaxial Layers Grown on (100) and (111) Oriented Silicon Substrates

2008 ◽  
Vol 600-603 ◽  
pp. 207-210 ◽  
Author(s):  
Marcin Zielinski ◽  
Marc Portail ◽  
Thierry Chassagne ◽  
Yvon Cordier
Keyword(s):  
Gaseous Phase ◽  
Growth Temperature ◽  
Growth Conditions ◽  
Silicon Substrates ◽  
Phase Growth ◽  
Growth Duration ◽  
Strain Control ◽  
Heteroepitaxial Layers ◽  
Oriented Layers ◽  
Sic Films

We discuss the influence of the growth conditions (composition of the gaseous phase, growth duration, growth temperature) and wafer properties (orientation, miscut, thickness) on the residual strain of 3C-SiC films grown on silicon substrates. We show that the strain related effects are observed for both studied orientations however some of them (namely the creep effects) were up to now stated only for (100) oriented layers. We also point out the main difference in strain control between the (111) and (100) orientations.

The effect of aliphatic chain length on thermal properties of poly(alkylene dicarboxylate)s

e-Polymers ◽  
2007 ◽  
Vol 7 (1) ◽  
Author(s):  
Corrado Berti ◽  
Annamaria Celli ◽  
Paola Marchese ◽  
Elisabetta Marianucci ◽  
Giancarlo Barbiroli ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Three Dimensional ◽  
The Other ◽  
Aliphatic Chain ◽  
Melting Temperatures ◽  
Avrami Analysis ◽  
Isothermal Analysis ◽  
Dimensional Growth ◽  
Crystallizing Polymers ◽  
Crystalline Forms

AbstractSome poly(alkylene dicarboxylate)s, derived from ethanediol or 1,4- butanediol and different diacids, have been synthesized and analyzed by DSC to determine the correlations existing between the thermal properties and the length of the aliphatic chain. The polymers show crystallization and melting temperatures and enthalpies which increase as the polymethylene segments lengthen, due to the formation of more stable crystals. The samples derived from ethanediol are peculiar; they show reorganization processes during the melting and the melting temperatures are notably higher with respect to those of the other polyesters. This behavior is discussed. Isothermal analysis highlights that poly(alkylene dicarboxylate)s are fast crystallizing polymers. The Avrami analysis suggests a crystallization mechanism characterized by heterogeneous nucleation and three dimensional growth; secondary crystallizations is present only in the samples characterized by short -(CH2)- sequences, due to the reorganization of less perfect crystalline forms. A comparative study between the crystallization rates as a function of the undercooling is reported.

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