Decomposition Of Arsine Research Articles

Thermal decomposition of arsine, a lewisite detoxification by-product

We developed the physicochemical principles of the thermal decomposition of arsine resulting from the electrochemical reduction of the products of lewisite detoxification by alkaline hydrolysis. The thermodynamic and kinetic parameters of the thermal dissociation of arsine were calculated for the temperature range of practical interest in order to minimize the arsine concentration in the effluent gas. A process was proposed and tested for processing lewisite detoxification products which includes the thermal decomposition of arsine. The resultant arsenic is 99.9999% pure. Based on the scientific and technological foundations of arsine pyrolysis, we designed a system for the thermal decomposition of arsine, which was integrated into a lewisite detoxification process.

Inter-element interferences in the determination of arsenic and antimony by hydride generation atomic absorption spectrometry with a quartz tube atomizer

The interferences between arsenic and antimony on each other during the hydride generation atomic absorption spectrometry (HGAAS) determination of arsenic and antimony using a quartz tube atomizer (QTA) were examined. In order to eliminate or reduce such interferences by selective heat decomposition of arsine and stibine, a Pyrex adsorption U-tube trap containing glass wool was placed between the drying tube and the quartz tube atomizer. Although at 250°C stibine decomposes and is held almost completely by the trap, arsine is also decomposed to an extent of 24% and, therefore, thermal decomposition is not useful to eliminate antimony interference on arsenic determination. The effect of coating the glass wool in the U-tube with antimony on the arsenic suppression of the antimony signal was studied. The results showed that the antimony coating in the U-tube could not hold arsenic effectively and its interference on the antimony signal could not be eliminated by this means. In the second part of the study, oxygen was supplied to the quartz tube atomizer during atomization in order to study the effect of supplying oxygen on the antimony signal and on the interference of arsenic in the antimony determination. Sensitivity was increased in the presence of oxygen and interferences of arsenic on antimony determination was decreased by about 10% when oxygen was supplied. It was also observed that the extent of interferences depended mainly on the interferent concentration rather than the analyte concentration.

A kinetic model for tris(dimethylamino) arsine decomposition on GaAs(100) surfaces

In this paper, we outline the detailed arguments involved in developing a kinetic model describing surface pyrolysis of tris(dimethylamino) arsine (TDMAAs) on a GaAs(100) surface. Two decomposition pathways of TDMAAs on GaAs(100) are assumed: simple scission of the arsenic and nitrogen bond and surface β-hydrogen transfer reaction. The pre-exponential factor for the scission of the parent is assumed to be the largest among the species going through the scission pathway. Removal of the last dimethylamino ligand is assumed to be essentially the rate-limiting step of the overall decomposition of TDMAAs. The reaction steps and constraints so constructed enable us to derive kinetic parameters of reasonable values from temperature-programmed desorption data in literature. Computer simulations based on the model reproduce well the behavior of data in literature of desorption products from a heated GaAs(100) surface exposed to TDMAAs inside a vacuum chamber.

Site-specific reaction kinetics for gallium arsenide metalorganic vapor-phase epitaxy

We have developed a kinetic model for arsine decomposition on GaAs(001) that accounts for the effect of the surface reconstructions on the rates of As4 and As2 desorption. The main assumption of the model is that As2 desorbs more slowly from Ga sites than from As sites. The model accurately simulates the temperature-programmed desorption of arsenic from GaAs(001). In addition, it reveals how the As coverage and the As2 and As4 production rates depend on the conditions employed during GaAs metalorganic vapor-phase epitaxy.

Behavior and mechanism of wide terrace formation during metalorganic vapor phase epitaxy of GaAs and related materials

We have investigated the behavior and mechanism of surface terrace formation during the annealing of GaAs in the presence of column-V gases and during the growth of GaAs, Al 0.35Ga 0.65As and AlAs by metalorganic vapor phase epitaxy (MOVPE) using atomic force microscopy. The ordered terrace arrays with monolayer-high steps are formed during annealing in arsine prior to growth. The width of the terraces formed during growth depends on the substrate misorientation angle. The critical terrace widths for two-dimensional nucleation for GaAs and AlGaAs are found to be similar, but those for AlAs are narrower. The widths for GaAs and AlGaAs grown by MOVPE are about one or two orders of magnitude larger than the widths for GaAs and Al 0.3Ga 0.7As grown by molecular beam epitaxy. However, a wide GaAs terrace is not formed when trimethylarsine (TMAs) is used as a column-V source. To explain wide terrace formation in MOVPE, we propose a hydrogen-radical terminated surface model and obtain results supporting this model. Hydrogen radicals generated from the decomposition of arsine enhance the surface of column-III species on H-terminated As atoms.

Arsine adsorption on Si(100) 2 x 1: A photoemission and scanning-tunneling-microscopy study.

We report on a study of the adsorption and decomposition of arsine molecules on clean Si(100) 2\ifmmode\times\else\texttimes\fi{}1 surfaces using photoemission and scanning tunneling microscopy (STM). Arsine decomposition depends on the substrate temperature and occurs in five regimes: (i) Below 100 \ifmmode^\circ\else\textdegree\fi{}C the arsine dissociatively adsorbs most likely into As-H and Si-H. At these temperatures there is negligible surface diffusion and the saturation arsenic coverage is 20% because the remaining Si sites do not have enough unoccupied near neighbors to provide four bonds for ${\mathrm{AsH}}_{3}$ adsorption. (ii) Between 100 \ifmmode^\circ\else\textdegree\fi{}C and 400 \ifmmode^\circ\else\textdegree\fi{}C the onset of surface diffusion increases the saturation coverage of As to 25% (i.e., one arsenic per four silicon atoms), As-As dimers form and coalesce into short chains. (iii) Above 400 \ifmmode^\circ\else\textdegree\fi{}C the hydrogen starts to desorb significantly thereby allowing larger As coverages. (iv) This process reaches an extremum at about 575 \ifmmode^\circ\else\textdegree\fi{}C where all hydrogen is desorbed resulting in nearly 100% As coverage. (v) Near 650 \ifmmode^\circ\else\textdegree\fi{}C the As desorption rate becomes significant. The STM images recorded in these regimes reveal a wide variety of surface structures which are due to different relative rates of ${\mathrm{AsH}}_{3}$ adsorption, H and As desorption, and H, As, and Si surface diffusion. The ${\mathrm{AsH}}_{3}$ adsorption and H and As desorption processes are discussed in the context of a kinetic model.

The growth of InAs 1- xSb x/InAs strained-layer superlattices by metalorganic chemical vapot deposition

InAs 1- x Sb x /InAs strained-layer superlattice (SLS) semiconductors and thick epitaxial layers of InAs 1- x Sb x were grown under a variety of conditions by metalorganic chemical vapor deposition on InAs substrates. The III/V ratio was varied from 0.026 to 1.0 over a temperature range of 475–525°C, at pressures of 200 to 660 Torr and growth rates of 0.75 to 3.0 μm/h. The composition of the ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. These layers were characterized by optical microscopy, secondary ion mass spectroscopy (SIMS), and X-ray diffraction. The optical properties of these SLSs were determined by infrared photoluminescence and absorption mneasurements.

Examination of Gallium Arsenide Mocvd Reaction Mechanisms

AbstractA mathematical model has been developed of the reactor used by Larsen et al. [1] to study the kinetics of gallium arsenide MOCVD.- Two different surface reactions were considered as the rate-limiting step in film growth below 500°C: (1) the desorption of methyl radicals from adsorbed trimethylgallium, and (2) the reaction of CH3 and H groups from adsorbed trimethylgallium and arsine to make methane. The latter step is consistent with the experimental results. It explains the rapid acceleration of the precursor decomposition rates when they are fed together to the reactor. It also explains why methane is the only hydrocarbon generated from trimethylgallium and arsine decomposition in deuterium at V/Ill ratios greater than 1.0.

The Growth of InAsSb/InGaAs Strained-Layer Superlattices by Metal-Organic Chemical Vapor Deposition

AbstractWe have grown InAsl-xSbx/Inl-yGayAs strained-layer superlattice (SLS) semiconductors lattice matched to InAs using a variety of conditions by metal-organic chemical vapor deposition. The V/III ratio was varied from 2.5 to 10 at a temperature of 475 °C, at pressures of 200 to 660 torr and growth rates of 3 - 5 A/s and layer thicknesses ranging from 55 to 152 Å. The composition of the InAsSb ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. Diodes have been prepared using Zn as the p-type dopant and undoped SLS as the n-type material. The diode was found to emit at 3.56 μm. These layers have been characterized by optical microscopy, SIMS, x-ray diffraction, and transmission electron diffraction. The optical properties of these SLS's were determined by infrared photoluminescence and absorption measurements.

The pyrolysis of precursors for GaAs MOCVD studied by in-situ and ex-situ Fourier transform infrared spectroscopy

The decomposition of arsine at atmospheric pressure as studied by in-situ and ex-situ Fourier transform infrared spectroscopy (FTIR) is presented, comparing the techniques. Ex-situ spectroscopic and spectrometric evidence for the formation of methylarsine and dimethylarsine during the reaction of trimethylgallium and arsine, and in-situ spectroscopic evidence for the formation of diethylarsine during the reaction of triethylgallium and arsine is discussed. The observation of alkylarsines strongly implies a stepwise free radical reaction mechanism, however whether these processes are heterogeneous or homogeneous remains uncler.

A thermal desorption investigation of arsine chemisorption on Ga-rich and As-rich GaAs(100) surfaces

We have studied the low temperature chemisorption of arsine on the Ga and As-rich surfaces of GaAs(100) using temperature programmed desorption. Arsine desorbing from the “(4 × 6)” Ga-rich surface desorbs from both molecular ( T p ≈165 K) and recombinative states ( T p =290 and 380 K) with an estimated saturation coverage of 0.09 ML, where 1 ML = 6.26 × 10 14 atoms/ cm 2. A very small amount of arsine is irreversibly adsorbed (approximately 0.01 ML) as evidenced by hydrogen desorption at about 520 K. This small arsine coverage suggests that most of the Ga atoms on the Ga-rich surface are not available for arsine chemisorption. On the c(2 × 8)/(2 × 4) As-rich GaAs(100) surface roughly two times more arsine desorbs compared to the Ga-rich surface and new desorption states are seen around 230 and 460 K. This increased arsine coverage suggests that most of the exposed Ga atoms on the As-rich surface are available for chemisorption. Approximately the same amount of arsine irreversibly decomposes on the c(2 × 8)/(2 × 4) As-rich surface (compared to the Ga-rich surface), but H 2 desorption occurs from a broad peak that is centered around 600 K. On the c(4 × 4) As-rich surface, arsine decomposition is not observed and only a small amount of arsine desorption is detected. This result is to be expected since there are no exposed Ga atoms on the c(4 × 4) surface.

Atomic layer epitaxy of GaAs using N 2 carrier gas

Carrier gas effects on the atomic layer epitaxial (ALE) conditions and the electrical quality of GaAs are investigated. ALE is achieved over a relatively wide temperature range of 490 to 520°C using nitrogen carrier gas. For hydrogen carrier gas, the corresponding temperature range for ALE growth is only from 490 to 500°C. Gas analysis of TMG reveals that this is due to the suppression of TMG decomposition in nitrogen. The use of nitrogen reduces carbon incorporation in the epilayers by about one order of magnitude (compared to hydrogen) by promoting the arsine decomposition. The stoichiometry of the ALE layer related to deep defects is clarified and a possible way to reduce them is proposed.

Thermal and Photoinduced Decomposition Pathways of Arsine on GaAs(100)

AbstractWe have studied the thermal and photoinduced dissociation pathway of AsH3 on the Ga-rich GaAs(100) surface. Arsine adsorbs molecularly at 115 K and dissociates upon either heating to above 140 K or upon irradiation with 3.5 - 6.4 eV photons. The decomposition of arsine is accompanied by the formation of surface Ga-H species, which are thermally and photochemically more stable than surface AsHx. A comparison of the wavelength dependence for adsorbed and gas phase arsine reveals that the excitation mechanism of the AsH3 surface photochemistry is substrate mediated, which probably involves a charge transfer between surface states and the adsorbate.

Deposition of Ga, Al and As Layers by Laser-Assisted Decomposition of Trimethylgallium, Trimethylaluminum and Arsine

We have investigated the substrate temperature dependence of deposition rates for Ga, Al and As layers formed on fused quartz (Suprasil) substrates by ArF excimer laser-assisted chemical vapor deposition using trimethylgallium, trimethylaluminum and arsine as source materials, respectively. The deposition rates for Ga and Al were independent of substrate temperature in the range from 100°C to 400°C, and then increased with substrate temperature above 400°C. On the other hand, the As deposition rate decreased dramatically with increasing substrate temperature up to 300°C. The result of As deposition can be explained qualitatively by three competing processes of the laser decomposition of arsine and laser and/or thermal desorptions of the As atom.

In Situ Diagnostics Of Epitaxial Growth Using Reflectance-Difference

ABSTRACTOptical in situ methods are becoming of increasing importance for studies of the mechanisms of growth and for real-time control of surface processes involved in epitaxial growth. We present data from studies, using the reflectance-difference (RD) method, of different processes related to epitaxial growth of GaAs (001) from arsine (AsH3) and from triethylgallium (TEG). RD studies make it possible to follow how the near-equilibrium, Ga-rich, configuration of the GaAs (001) surface changes with temperature and we show how the transformation to this state can be followed from As-saturated as well as from Ga-saturated surfaces. From the initial slope of the RD-transient, corresponding to the AsH3 reaction with a Ga-stabilized surface, the temperature dependence of the catalytic effect of this surface on the decomposition of arsine is measured. Of special significance for an atomic layer epitaxial process (ALE) is the demonstration of a self-limiting reaction of TEG. This process can be followed as the surface modifies itself from a state obtained by exposure to excess TEG to the near-equilibrium Ga-terminated reconstruction. Finally, we demonstrate how pulsing sequences for the realization of ALE can be followed and controlled in real time using RD as a diagnostic tool.

Decomposition kinetics of III–V materials used for MOCVD epitaxial growth

The decomposition reaction mechanism was experimentally investigated for TMG and arsine used for MOCVD GaAs epitaxial growth. The obtained TMG conversion in H 2 showed a decrease-minimum-increase change, as the amount of coexisting arsine was increased. This indicates that the decomposition proceeds according to the following reactions: (1) CH 3 elimination, (2) arsine decomposition on the GaAs surface, (3) TMG-H 2 reaction (hydrogenolysis), (4) hydrogen radical formation from CH 3-H 2 reaction, (5) TMG-hydrogen radical reaction, (6) arsine-hydrogen radical reaction, and (7) TMG-arsine reaction on the GaAs surface. The experimental results are explained by assuming the relative magnitudes of the above reaction rates. It is suggested that the arsine-hydrogen radical reaction (6) takes place at a much higher rate than TMG-hydrogen radical reaction (5) and the TMG-arsine surface reaction (7) takes place much more slowly than the CH 3 elimination reaction (1).

Electrical and optical properties of RF glow discharges of amorphous Ga xAs 1− x films

Amorphous Ga x As 1− x thin films were prepared by a deposition process based on the sputtering of a gallium target and arsine decomposition in an RF glow discharge. DC electrical and optical properties of films, particularly around the stoichiometry, were recorded and related to the experimental conditions such as outgassing, plasma hydrogenation and deposition temperature. The properties of our material seem to be improved by a slight excess of arsenic in the films.

Preparation and properties of Arsenic thin films deposited by Mercury-photosensitized chemical vapor deposition

Deposition of arsenic thin films on quartz substrates utilizing mercury-photosensitized decomposition of arsine is reported. The deposition process is discussed and a simple model is proposed suggesting that the rate-limiting step in the deposition process involves the collision between the excited mercury atoms and arsine molecules. In addition, the arsenic thin films obtained using this technique are characterized utilizing X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, optical absorption and cold vapor atomic absorption spectrometry. Results of this characterization indicate minor differences in the optical absorption spectra for the amorphous arsenic thin films deposited by means of Hg-photosensitization as opposed to films obtained by sputtering or evaporation. In this work, rhombohedral arsenic thin films were obtained at a substrate temperature of 240°C and amorphous films were obtained at substrate temperatures less than 150°C.

The Role of Arsine in Reducing Carbon in Triethylarsenic Grown GaAs Films

AbstractVery high carbon impurity levels (1018-1021cm−3) in GaAs films grown using triethylarsenic (Et3As) and trimethylgallium (Me3Ga) can be dramatically reduced by substituting a portion of the Et3As reagent with arsine during growth. Gallium arsenide epilayers grown at a deposition temperature of 560°C, a total V/III ratio =10, and the Group V reagent consisting of a mixture of Et3As and arsine, were found to exhibit carbon levels of only 5-7×1015cm−3for Group V mixtures ranging from 0-65% Et3As. All of these films were n-type, except for those grown using 100% arsine, which were p-type. The reduction in carbon incorporation in films grown using Et3As and arsine as co-reagents is shown to result from a unique, synergistic, reaction chemistry involving the two arsenic reagents. In particular, the decomposition of arsine to provide carbon-free, active arsenic fragments for growth is greatly enhanced by the presence of Et3As as a co-reactant.

Phosphine and arsine decomposition in CVD reactors for InP and InGaAs growth

A model of phosphine and arsine decomposition is developed that permits the taking into account of real partial pressure of hybrides in a CVD reactor for InP and InGaAs growth. It agrees with experimental results and explains the existence of two growth regimes of InP.