Models and Mechanisms of III-V Compound Semiconductor Growth by Movpe

1989 ◽  
Vol 145 ◽  
Author(s):  
Klavs F. Jensen ◽  
Triantafillos J. Mountziaris ◽  
Dimitrios I. Fotiadis
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Transport Phenomena ◽  
Reaction Model ◽  
Reactor Performance ◽  
Gas Phase Reactions ◽  
Carbon Incorporation ◽  
Transport Reaction ◽  
Model Predictions ◽  
Good Agreement

AbstractA kinetic model for metalorganic vapor phase epitaxy (MOVPE) of GaAs from trimethylgallium and arsine is imbedded into two-dimensional transport phenomena descriptions of horizontal and vertical MOVPE reactors. The mechanism involves 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 26 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Carbon incorporation is predicted to occur via carbene containing species. A sensitivity analysis shows that only a few reactions are needed to simulate observed growth rates while the full mechanism is important in computing carbon levels in GaAs. The model predictions are in good agreement with data for trimethylgallium decomposition in hot isothermal tubes, with GaAs growth in horizontal reactors, and with carbon incorporation in vertical reactors. The transport-reaction model demonstrates that both gas-phase and surface reactions as well as transport phenomena are important in predicting MOVPE reactor performance.

Gas Phase and Surface Reactions in Mocvd of GaAs from Triethylgallium, Trimethylgallium, and Organometallic Arsenic Precursors

1988 ◽  
Vol 131 ◽  
Author(s):  
Thomas R. Omstead ◽  
Penny M. Van Sickle ◽  
Klavs F. Jensen
Keyword(s):  
Gas Phase ◽  
Low Temperatures ◽  
Surface Reactions ◽  
Rate Data ◽  
Gas Phase Reactions ◽  
Heated Zone ◽  
Model Predictions ◽  
First Time ◽  
Good Agreement

ABSTRACTThe growth of GaAs from triethylgallium (TEG) and trimethylgallium (TMG) with tertiarybutylarsine (tBAs), triethylarsenic (TEAs), and trimethylarsenic (TMAs), has been investigated by using a reactor equipped with a recording microbalance for in situ rate measurements. Rate data show that the growth with these precursors is dominated by the formation of adduct compounds in the gas lines, by adduct related parasitic gas phase reactions in the heated zone, and by the surface reactions. A model is proposed for the competition between deposition reactions and the parasitic gas phase reactions. Model predictions are in very good agreement with experimental data for all combinations of precursors except for TEG/TMAs where extensive gallium droplet formation is observed at low temperatures. Growth of reasonable quality GaAs with Hall mobilities of 7600 cm2/Vs at 77 K using TEG and tBAs is reported for the first time.

Homogeneous Oxidation of Hydrogen in Catalytic Mini/Microchannels

2011 ◽  
Author(s):  
Azad Qazi Zade ◽  
Metin Renksizbulut ◽  
Jacob Friedman
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Operating Conditions ◽  
Planar Geometry ◽  
Channel Height ◽  
Phase Reaction ◽  
Gas Phase Reactions ◽  
Radical Chain ◽  
Oxidation Of Hydrogen ◽  
Volume Method

Gas phase reaction effects in the catalytic oxidation of hydrogen on platinum-coated minichannels and microchannels are investigated numerically in planar geometry. The main objective of this work is to identify the relative importance of the gas phase and surface reactions under different operating conditions. A collocated finite-volume method is used to solve the governing equations. Detailed gas phase and surface reaction mechanisms along with a multi-component diffusion model are used. As the channel size is reduced, heat and radical losses to the walls can significantly alter the combustion behavior. While catalytic walls help in sustaining the gas phase reactions at very small length scales by reducing the heat losses to the walls owing to heat release associated with the surface reactions, they may inhibit homogeneous reactions by extracting radicals due to typically high absorption rates of such species at the walls. Thus, the radical chain mechanisms can be significantly altered by the presence of wall reactions, and the build-up of radical pools in the gas phase, which lead to homogeneous ignition, can be suppressed as a consequence. In the present study, the effects of two key parameters, i.e. channel height and the inlet mass flux on the interaction of gas phase and surface reactions will be explored. In each case, the limiting values beyond which the gas-phase reactions become relatively negligible compared to surface reactions will be identified for hydrogen/air mixtures.

scholarly journals Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

1993 ◽  
Vol 335 ◽  
Author(s):  
Suleyman A. Gokoglu ◽  
G. D. Stewart ◽  
J. Collins ◽  
D. E. Rosner
Keyword(s):  
Gas Phase ◽  
Impinging Jet ◽  
Gas Phase Reactions ◽  
Reactor Model ◽  
Deposition Rates ◽  
Numerical Predictions ◽  
Model Predictions ◽  
Phase Nucleation ◽  
Chemically Reacting ◽  
The Mathematical Model

AbstractWe model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (∼11% at 1000K), the reduction of rates due to Soret transport is substantial (∼75% at 1000K).

Transport-Reaction Model of Mural Thrombogenesis: Comparisons of Mathematical Model Predictions and Results from Baboon Models

2010 ◽  
Vol 38 (8) ◽  
pp. 2660-2675 ◽  
Author(s):  
Sandra Rugonyi ◽  
Erik Tucker ◽  
Ulla Marzec ◽  
Andras Gruber ◽  
Stephen Hanson
Keyword(s):  
Mathematical Model ◽  
Reaction Model ◽  
Transport Reaction ◽  
Model Predictions

scholarly journals Chemical Characteristics of Embedded Young Stellar Objects

2000 ◽  
Vol 197 ◽  
pp. 71-80
Author(s):  
Michiel R. Hogerheijde
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Young Stellar Objects ◽  
Chemical Characteristics ◽  
Dust Grains ◽  
Gas Phase Reactions ◽  
Stellar Objects ◽  
Grain Surface ◽  
Theoretical Considerations

Based on theoretical considerations, the chemistry around embedded young stellar objects is expected to be governed by the interplay between gas-phase reactions, condensation of molecules onto dust grains, grain surface reactions, and evaporation of altered ice mantles near the star and in the outflow. I discuss the chemical characteristics of embedded young stellar objects, with special emphasis on these processes.

COMPUTER MODELING OF CHEMICAL EQUILIBRIUMS IN WO3–H2O SYSTEM

2017 ◽  
pp. 35-48 ◽  
Author(s):  
V.P. Bondarenko ◽  
O.O. Matviichuk
Keyword(s):  
Transition Temperature ◽  
Gas Phase ◽  
Single Phase ◽  
Reference Data ◽  
Maximum Amount ◽  
Reaction Products ◽  
Influence Of Temperature ◽  
Equilibrium Chemical ◽  
Program Data ◽  
Good Agreement

Detail investigation of equilibrium chemical reactions in WO3–H2O system using computer program FacktSage with the aim to establish influence of temperature and quantity of water on formation of compounds of H2WO4 and WO2(OH)2 as well as concomitant them compounds, evaporation products, decomposition and dissociation, that are contained in the program data base were carried out. Calculations in the temperature range from 100 to 3000 °С were carried out. The amount moles of water added to 1 mole of WO3 was varied from 0 to 27. It is found that the obtained data by the melting and evaporation temperatures of single-phase WO3 are in good agreement with the reference data and provide additionally detailed information on the composition of the gas phase. It was shown that under heating of 1 mole single-phase WO3 up to 3000 °С the predominant oxide that exist in gaseous phase is (WO3)2. Reactions of it formation from other oxides ((WO3)3 and (WO3)4) were proposed. It was established that compound H2WO4 is stable and it is decomposed on WO3 and H2O under 121 °C. Tungsten Oxide Hydrate WO2(OH)2 first appears under 400 °С and exists up to 3000 °С. Increasing quantity of Н2О in system leads to decreasing transition temperature of WO3 into both liquid and gaseous phases. It was established that adding to 1 mole WO3 26 mole H2O maximum amount (0,9044–0,9171 mole) WO2(OH)2 under temperatures 1400–1600 °С can be obtained, wherein the melting stage of WO3 is omitted. Obtained data also allowed to state that that from 121 till 400 °С WO3–Н2O the section in the О–W–H ternary system is partially quasi-binary because under these temperatures in the system only WO3 and Н2O are present. Under higher temperatures WO3–Н2O section becomes not quasi-binary since in the reaction products WO3 with Н2O except WO3 and Н2O, there are significant amounts of WO2(OH)2, (WO3)2, (WO3)3, (WO3)4 and a small amount of atoms and other compounds. Bibl. 12, Fig. 6, Tab. 5.

Explaining the magnetism of gold

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Gas Phase ◽  
Computational Study ◽  
Formation Enthalpy ◽  
Gold Atom ◽  
Orbital Energy ◽  
Knudsen Effusion ◽  
Energy Diagram ◽  
Unpaired Electrons ◽  
The Difference ◽  
Good Agreement

<p>In the present work, a computational study is performed in order to clarify the possible magnetic nature of gold. For such purpose, gas phase Au<sub>2</sub> (zero charge) is modelled, in order to calculate its gas phase formation enthalpy. The calculated values were compared with the experimental value obtained by means of Knudsen effusion mass spectrometric studies [5]. Based on the obtained formation enthalpy values for Au<sub>2</sub>, the compound with two unpaired electrons is the most probable one. The calculated ionization energy of modelled Au<sub>2</sub> with two unpaired electrons is 8.94 eV and with zero unpaired electrons, 11.42 eV. The difference (11.42-8.94 = 2.48 eV = 239.29 kJmol<sup>-1</sup>), is in very good agreement with the experimental value of 226.2 ± 0.5 kJmol<sup>-1</sup> to the Au-Au bond<sup>7</sup>. So, as expected, in the specie with none unpaired electrons, the two 6s<sup>1</sup> (one of each gold atom) are paired, forming a chemical bond with bond order 1. On the other hand, in Au<sub>2</sub> with two unpaired electrons, the s-d hybridization prevails, because the relativistic contributions. A molecular orbital energy diagram for gas phase Au<sub>2</sub> is proposed, explaining its paramagnetism (and, by extension, the paramagnetism of gold clusters and nanoparticles).</p>

Sign in / Sign up

Export Citation Format

Share Document