Structural Properties of Nitrides Grown by Omvpe on Sapphire Substrate

1997 ◽  
Vol 482 ◽  
Author(s):  
H. Amano ◽  
T. Takeuchi ◽  
S. Yamaguchi ◽  
S. Nitta ◽  
M. Kariya ◽  
...  
Keyword(s):  
Low Temperature ◽  
Buffer Layer ◽  
Structural Properties ◽  
Sapphire Substrate ◽  
Crystallization Process ◽  
Free Standing ◽  
In Situ Observations ◽  
Gan Buffer Layer

AbstractCrystalline quality of nitrides on sapphire by OMVPE has been investigated. First, in-situ observations of the crystallization process of the low temperature deposited AIN buffer layer or GaN buffer layer on sapphire substrate have been performed. Small hexagonal mesas were formed from the sapphire to the surface and finally they formed a stacked structure. Secondly, a low temperature deposited buffer layer located between the high temperature grown GaN was found to reduce the etch pit density of GaN films. Thirdly, structural properties of Ga1−xInxN (0 ≤x≤0.21, and x= l) on GaN and GaInN/GaN MQWs on GaN have been characterized by Xray diffraction. Coherently grown GaInN showed almost the same twisting as the underlying GaN layer, while free standing InN showed large twisting. Thickness of the well layers in MQWs has been controlled within one monolayer preciseness, and the fluctuation of alloy composition has been controlled to within 2%

scholarly journals Morphology and surface reconstructions of m-plane GaN

2002 ◽  
Vol 743 ◽  
Author(s):  
C. D. Lee ◽  
R. M. Feenstra ◽  
J. E. Northrup ◽  
L. Lymperakis ◽  
J. Neugebauer
Keyword(s):  
Molecular Beam Epitaxy ◽  
Low Temperature ◽  
Surface Morphology ◽  
Buffer Layer ◽  
Molecular Beam ◽  
Structural Quality ◽  
Surface Reconstructions ◽  
Gan Buffer Layer

ABSTRACTM-plane GaN(1100) is grown by plasma assisted molecular beam epitaxy on ZnO(1100) substrates. A low-temperature GaN buffer layer is found to be necessary to obtain good structural quality of the films. Well oriented (1100) GaN films are obtained, with a slate like surface morphology. On the GaN(1100) surfaces, reconstructions with symmetry of c(2×2) and approximate “4×5” are found under N- and Ga-rich conditions, respectively. We propose a model for Ga-rich conditions with the “4×5” structure consisting of ≥ 2 monolayers of Ga terminating the GaN surface.

The Influence of Growth Temperature on Oxygen Concentration in GaN Buffer Layer

2008 ◽  
Vol 1068 ◽  
Author(s):  
Ewa Dumiszewska ◽  
Wlodek Strupinski ◽  
Piotr Caban ◽  
Marek Wesolowski ◽  
Dariusz Lenkiewicz ◽  
...  
Keyword(s):  
High Temperature ◽  
Buffer Layer ◽  
Oxygen Concentration ◽  
Growth Temperature ◽  
Low Temperatures ◽  
Buffer Layers ◽  
Crystalline Quality ◽  
Temperature Growth ◽  
Gan Buffer Layer

ABSTRACTThe influence of growth temperature on oxygen incorporation into GaN epitaxial layers was studied. GaN layers deposited at low temperatures were characterized by much higher oxygen concentration than those deposited at high temperature typically used for epitaxial growth. GaN buffer layers (HT GaN) about 1 μm thick were deposited on GaN nucleation layers (NL) with various thicknesses. The influence of NL thickness on crystalline quality and oxygen concentration of HT GaN layers were studied using RBS and SIMS. With increasing thickness of NL the crystalline quality of GaN buffer layers deteriorates and the oxygen concentration increases. It was observed that oxygen atoms incorporated at low temperature in NL diffuse into GaN buffer layer during high temperature growth as a consequence GaN NL is the source for unintentional oxygen doping.

Novel in situ self-separation of a 2 in. free-standing m-plane GaN wafer from an m-plane sapphire substrate by HCl chemical reaction etching in hydride vapor-phase epitaxy

CrystEngComm ◽  
2016 ◽  
Vol 18 (40) ◽  
pp. 7690-7695
Author(s):  
Seohwi Woo ◽  
Sangil Lee ◽  
Uiho Choi ◽  
Hyunjae Lee ◽  
Minho Kim ◽  
...  
Keyword(s):  
Chemical Reaction ◽  
Vapor Phase ◽  
Sapphire Substrate ◽  
Vapor Phase Epitaxy ◽  
Hydride Vapor Phase Epitaxy ◽  
Free Standing

A 2 in.-diameter free-standing m-plane GaN wafer was fabricated through in situ self-separation from m-plane sapphire using HCl chemical reaction etching (HCRE) in hydride vapor-phase epitaxy (HVPE).

scholarly journals The extreme runoff index for flood early warning in Europe

2014 ◽  
Vol 14 (6) ◽  
pp. 1505-1515 ◽  
Author(s):  
L. Alfieri ◽  
F. Pappenberger ◽  
F. Wetterhall
Keyword(s):  
Early Warning ◽  
Input Data ◽  
Weather Forecasting ◽  
Spatial Inhomogeneity ◽  
Optimal Timing ◽  
Numerical Predictions ◽  
In Situ Observations

Abstract. Systems for the early detection of floods over continental and global domains have a key role in providing a quick overview of areas at risk, raise the awareness and prompt higher detail analyses as the events approach. However, the reliability of these systems is prone to spatial inhomogeneity, depending on the quality of the underlying input data and local calibration. This work proposes a simple approach for flood early warning based on ensemble numerical predictions of surface runoff provided by weather forecasting centers. The system is based on a novel indicator, referred to as an extreme runoff index (ERI), which is calculated from the input data through a statistical analysis. It is designed for use in large or poorly gauged domains, as no local knowledge or in situ observations are needed for its setup. Daily runs over 32 months are evaluated against calibrated hydrological simulations for all of Europe. Results show skillful flood early warning capabilities up to a 10-day lead time. A dedicated analysis is performed to investigate the optimal timing of forecasts to maximize the detection of extreme events. A case study for the central European floods of June 2013 is presented and forecasts are compared to the output of a hydro-meteorological ensemble model.

In situ UV monitoring of wastewater: a response to sample aging

2004 ◽  
Vol 49 (1) ◽  
pp. 47-52 ◽  
Author(s):  
E. Baurès ◽  
C. Berho ◽  
M.-F. Pouet ◽  
O. Thomas
Keyword(s):  
Low Temperature ◽  
Process Control ◽  
Treated Wastewater ◽  
Wastewater Sample ◽  
Line Measurement ◽  
Regulation Compliance

The phenomenon of wastewater sample aging is supposed to be treated with a low temperature autosampler. This work presents two examples of treated wastewater, the quality of which varies with the time of conservation. This evolution may pose some problems with respect to regulation compliance or process control. After the explanation of the mechanisms involved in sample aging, some recommendations are proposed in order to improve the UV off-line measurement of TSS and COD of treated wastewater.

scholarly journals Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale

Holzforschung ◽  
2020 ◽  
Vol 74 (5) ◽  
pp. 477-487 ◽  
Author(s):  
Jenny Carlsson ◽  
Magnus Heldin ◽  
Per Isaksson ◽  
Urban Wiklund
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
X Ray ◽  
Tool Geometries ◽  
Commercial Use ◽  
X Ray Computed ◽  
In Situ Observations ◽  
Underlying Mechanisms

AbstractWith industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.

Influence of substrate polarity on the low-temperature GaN buffer layer growth on GaAs (111)A and (111)B surfaces

2003 ◽  
Vol 247 (3-4) ◽  
pp. 245-250 ◽  
Author(s):  
Hisashi Murakami ◽  
Yoshinao Kumagai ◽  
Hisashi Seki ◽  
Akinori Koukitu
Keyword(s):  
Low Temperature ◽  
Buffer Layer ◽  
Layer Growth ◽  
Influence Of Substrate ◽  
Gan Buffer Layer
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