MOVPE GaN Gas-Phase Chemistry for Reactor Design and Optimization

1996 ◽  
Vol 449 ◽  
Author(s):  
S. A. Safvi ◽  
J. M. Redwing ◽  
A. Thon ◽  
J. S. Flynn ◽  
M. A. Tischler ◽  
...  
Keyword(s):  
Growth Rate ◽  
Gas Phase ◽  
Growth Rates ◽  
Operating Conditions ◽  
Gas Phase Reactions ◽  
Group V ◽  
Group Iii ◽  
Design And Optimization ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

ABSTRACTThe results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligmerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

Atomie Layer Epitaxy ia a Rotating Disk Reactor

1991 ◽  
Vol 240 ◽  
Author(s):  
H. Liu ◽  
P. A. Zawadzki ◽  
P. E. Norris
Keyword(s):  
Growth Rate ◽  
Gas Phase ◽  
Atomic Layer ◽  
Rotating Disk ◽  
Atomic Layer Epitaxy ◽  
Process Window ◽  
Phase Reaction ◽  
Gas Phase Reactions ◽  
Group Iii ◽  
Reaction Complex

ABSTRACTCurrent difficulties of Atomic Layer Epitaxy (ALE) include relatively low growth rates and narrow process windows. Gas phase reaction, complex behavior of valve switching and purging times are suggested as the major causes [1,2]. We have used a movable X-shaped mechanical barrier to divide the growth chamber into four zones. Each zone supplies either source gas or purging hydrogen. If the barrier is positioned 0.5–2 mm from the wafer carrier, it can efficiently shear off the boundary layer and therefore reduce gas phase reactions. The substrate, constantly rotating beneath the barrier, is alternately exposed to group III or V sources by purging zones. The result is that process times are significantly reduced, saturated growth rate of 1 μm/hour is obtained and a relatively wide process window is observed. It was found that the growth mode was not purely ALE, due to source gas mixing which contributes an additional, possible kinetically limited, component of growth rate. However, this was also found to result in uniform film.

Si + SiH4 Reactions and Implications for Hot-Wire CVD of a-Si:H: Computational Studies

2000 ◽  
Vol 609 ◽  
Author(s):  
Richard P. Muller ◽  
Jason K. Holt ◽  
David G. Goodwin ◽  
William A. Goddard
Keyword(s):  
Quantum Chemistry ◽  
Amorphous Silicon ◽  
Gas Phase ◽  
Computational Studies ◽  
Hot Wire ◽  
Gas Phase Reactions ◽  
High Quality ◽  
Gas Phase Chemistry ◽  
Si Films ◽  
Phase Chemistry

ABSTRACTGas phase chemistry is believed to play an important role in hot-wire CVD of amorphous silicon, serving to convert the highly-reactive atomic Si produced at the wire into a less-reactive species by reaction with ambient SiH4. In this paper, we use quantum chemistry computations (B3LYP/cc-pvTZ) to examine the energetics and rates of possible gas-phase reactions between Si and SiH4. The results indicate that formation of disilyne (Si2H2) is energetically favorable. Unlike other products of this reaction, Si2H2 does not require collisional stabilization, and thus this species is the most likely candidate for a benevolent precursor that participates in the growth of high-quality Si films.

Oxidative dealkylation of aromatic amines by "bare" FeO+ in the gas phase

1999 ◽  
Vol 77 (5-6) ◽  
pp. 774-780 ◽  
Author(s):  
Mark Brönstrup ◽  
Detlef Schröder ◽  
Helmut Schwarz
Keyword(s):  
Gas Phase ◽  
Bond Activation ◽  
Isotope Effects ◽  
Gas Phase Reactions ◽  
Electron Transfer Mechanism ◽  
Gas Phase Chemistry ◽  
Kinetic Isotope ◽  
Phase Chemistry ◽  
Cytochrome P 450 ◽  
Mass Spectrometric Techniques

The gas-phase oxidations of aniline, N-methylaniline, and N,N-dimethylaniline by FeO+ cation are examined by using mass spectrometric techniques. Although bare FeO+ is capable of hydroxylating aromatic C—H bonds, the fate of the oxidation of arylamines is determined by docking of the FeO+ unit at nitrogen. The major reactions of the metastable aniline/FeO+ complex are losses of molecular hydrogen, ammonia, and water, all involving at least one N-H proton. N-alkylation results in a complete shift of the course of the reaction. The unimolecular processes observed can be regarded as initial steps of an oxidative dealkylation of the amines mediated by FeO+. More detailed mechanistic insight is obtained by examining the C—H(D) bond activation of N-methyl-N-([D3]-methyl)aniline by bare and ligated FeO+ species. The gas-phase reactions of FeO+ with methylanilines show some similarities to the enzymatic dealkylation of amines by cytochrome P-450. The kinetic isotope effects observed experimentally suggest an electron transfer mechanism for the gas-phase reaction.Key words: mass spectrometry, gas-phase chemistry, iron, dealkylation, N,N-dimethylaniline.

The Effect of Phosphine Pressure on the Band Gap of Ga0.5In0.5P

1994 ◽  
Vol 340 ◽  
Author(s):  
Sarah R. Kurtz ◽  
D. J. Arent ◽  
K. A. Bertness ◽  
J. M. Olson
Keyword(s):  
Growth Rate ◽  
Surface Structure ◽  
Band Gap ◽  
Surface Diffusion ◽  
Parameter Space ◽  
Growth Temperature ◽  
Growth Rates ◽  
Diffusion Length ◽  
Group V ◽  
Group Iii

ABSTRACTThe band gap of Ga0.51n0.5P is studied as a function of phosphine pressure, B-type substrate misorientation, growth rate, and growth temperature, with emphasis placed on the effect of the phosphine pressure. Over most of the parameter space explored (high temperatures, large substrate misorientations, and low growth rates), the band gap increases with decreasing phosphine. This increase is proposed to be caused by lower phosphorus coverage of the surface, resulting in a different surface structure that doesn't promote ordering. The implications of this effect on the observed variations of band gap with growth temperature, substrate misorientation, and growth rate are discussed. For regions of parameter space in which the ordering appears to be kinetically limited by surface diffusion, the band gap increases slightly with phosphine pressure, consistent with observations that increased group-V pressure decreases the group-III surface diffusion length.

Effect of Growth Parameters and Local Gas-Phase Concentrations on the Uniformity and Material Properties of GaN/Sapphire Grown by Hydride Vapor-Phase Epitaxy

1996 ◽  
Vol 449 ◽  
Author(s):  
S. A. Safvi ◽  
N. R. Perkins ◽  
M. N. Horton ◽  
T. F. Kuech
Keyword(s):  
Gas Phase ◽  
Vapor Phase ◽  
Growth Parameters ◽  
Ammonia Concentration ◽  
Vapor Phase Epitaxy ◽  
Operating Conditions ◽  
Hydride Vapor Phase Epitaxy ◽  
Crystal Quality ◽  
Group V ◽  
Group Iii

ABSTRACTThe effects of flowrate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal Gallium Nitride vapor phase epitaxy reactor. To better understand the effects of these parameters, numerical model predictions are compared to experimentally observed values. Parasitic gas phase reactions between group III and group V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V/III ratio and an ammonia concentration lead to poor crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize these parasitic reactions and wall deposition while providing a uniform reactant distribution across the substrate.

A Model of the Gas-Phase Chemistry of Boron Nitride CVD From BCl3 and NH 3*

1995 ◽  
Vol 410 ◽  
Author(s):  
Mark D. Allendorf ◽  
Carl F. Melius ◽  
Thomas H. Osterheld
Keyword(s):  
Boron Nitride ◽  
Gas Phase ◽  
Plug Flow ◽  
Unimolecular Decomposition ◽  
Gas Phase Reactions ◽  
Gas Phase Chemistry ◽  
Theoretical Predictions ◽  
Phase Precursor ◽  
Phase Chemistry ◽  
Kinetics Of

ABSTRACTThe kinetics of gas-phase reactions occurring during the CVD of boron nitride (BN) from BCl3 and NH3 are investigated using an elementary reaction mechanism whose rate constants were obtained from theoretical predictions and literature sources. Plug-flow calculations using this mechanism predict that unimolecular decomposition of BCl3 is not significant under typical CVD conditions, but that some NH3 decomposition may occur, especially for deposition occurring at atmospheric pressure. Reaction of BCl3 with NH3 is rapid under CVD conditions and yields species containing both boron and nitrogen. One of these compounds, Cl2BNH2, is predicted to be a key gas-phase precursor to BN.

Towards an advanced description and modelling of the atmospheric multiphase chemistry of mercury: CAPRAM HG module 1.0

2021 ◽  
Author(s):  
Erik Hans Hoffmann ◽  
Tao Li ◽  
Andreas Tilgner ◽  
Yan Wang ◽  
Hartmut Herrmann
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Aerosol Particles ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Gas Phase Reactions ◽  
Gaseous Elemental Mercury ◽  
Gas Phase Chemistry ◽  
Reactive Halogen Species ◽  
Phase Chemistry

<p>Mercury is a neurotoxic element emitted predominantly in its less-reactive form as gaseous elemental mercury (GEM) into the atmosphere by various natural and anthropogenic processes. Once emitted it undergoes chemical processing in the atmospheric gas and aqueous phase. There, GEM is oxidised into gaseous oxidised mercury (GOM), which partitions into aerosol particles residing there as particulate bounded mercury (PBM) due to its much higher solubility. The faster deposition of GOM and PBM compared to GEM is of special environmental importance, because they can be converted into more toxic organic mercury in aquatic environments and then take serious place in the food web. Thus, it is crucial for models to understand the transformation of GEM into GOM and PBM and vice versa. To date, numerous gas-phase chemistry simulations were performed, but reveal missing oxidation and reduction processes. However, only few models exist that investigate the multiphase mercury chemistry in a detailed manner.</p><p>Therefore, a comprehensive multiphase mercury chemistry mechanism, the CAPRAM HG module 1.0 (CAPRAM-HG1.0), has been developed. The CAPRAM-HG1.0 includes 74 gas-phase reactions, 22 phase transfers and 77 aqueous-phase reactions. It was coupled to the multiphase chemistry mechanism MCMv3.2/CAPRAM4.0 and the extended CAPRAM halogen module 3.0 (CAPRAM-HM3.0) for investigations of multiphase Hg redox under Chinese polluted conditions. Simulations were performed for summer conditions in 2014 using the air parcel model SPACCIM to investigate the performance of the model to simulate typical concentrations and patterns of GEM, GOM and PBM.</p><p>Under non-cloud conditions, model results reveal good coincides with concentrations and patterns for GEM, GOM and PBM measured in China. However, the simulations also show that there are still high uncertainties in atmospheric mercury chemistry. Especially, the complexation with HULIS within aerosol particles needs evaluation as the simulations indicate this process as key process driving concentrations and patterns of both GOM and PBM. Further, the present study demonstrates the need of a better understanding of continental concentrations of reactive halogen species and particle bounded halides as well as their link to the multiphase chemistry and atmospheric cycling of mercury.</p>

scholarly journals The Role of Grains in Interstellar Chemistry

1987 ◽  
Vol 120 ◽  
pp. 531-538
Author(s):  
D. A. Williams
Keyword(s):  
Gas Phase ◽  
Mantle Material ◽  
Gas Phase Reactions ◽  
Hot Stars ◽  
Interstellar Chemistry ◽  
Chemical Erosion ◽  
Gas Phase Chemistry ◽  
Plausible Mechanism ◽  
Phase Chemistry

Grains affect interstellar chemistry in a variety of ways. Most obviously, they extinguish starlight and thus protect molecules in cloud interiors from photodestruction. The grains themselves contain substantial proportions of particular elements which are therefore less readily available for gas phase reactions and for processing into molecules. Grains in dense clouds are known to accrete molecular mantles which may be further processed; the mantle material is ultimately returned to the gas, either near hot stars or when the clouds are dissipated. Molecular hydrogen, the key to all gas phase chemistry, is undoubtedly formed efficiently on grains, and a plausible mechanism can now be identified. Other molecules, too, form preferentially at surfaces. Finally, the destruction of grains via chemical erosion and by sputtering in shocks provides a substantial molecular contribution to the gas in local regions.

Sign in / Sign up

Export Citation Format

Share Document