Reaction Of Trimethylgallium Research Articles

The effects of surface composition on the reaction of trimethylgallium on Si(100) and on aluminum and gallium treated Si(100)

The adsorption and decomposition of trimethylgallium (TMGa) on clean Si(100) and on gallium and aluminum covered Si(100) is examined with temperature desorption spectroscopy (TDS) and Auger electron spectroscopy. At coverages below 2.5 × 10 13 TMGa molecules cm 2 on clean Si(100), dosed at 100 K, the TDS products are methane (370 K, 500 K), hydrogen (800 K) and atomic gallium (970 K). At coverages near 0.5 × 10 14 molecules cm 2 additional products, TMGa (370 K) and ethylene (570 K), are observed. At multilayer coverages, 2.5 × 10 14 molecules cm 2 , there are new desorption signals which result from the multilayer desorption peak of TMGa (140 K), and the desorption of dimethylgallium (350–550 K), monomethylgallium (550–750 K), a second ethylene peak (740 K), and methyl species (770 K). The presence of 0.3 ML or more of gallium or aluminum on Si(100) drastically alters the reaction pathway, desorption of TMGa is favored on the gallium treated surface, whereas decomposition is favored on the clean silicon surface. More than twice as much gallium is deposited from TMGa on the untreated Si(100)2 × 1 surface than on a 0.5 ML gallium treated Si(100) surface. On the aluminum treated surface, desorption of gallium organometallic species is completely suppressed above the multilayer desorption temperature (140 K) and instead methyl groups are transferred from TMGa to aluminum atoms. Trimethylaluminum (TMA1) and dimethylaluminum (DMA1) are detected as desorption products, desorption of these species increases with increased aluminum coverage. There is more net gallium deposited from TMGa on the aluminum treated Si(100) surface than on the gallium treated surface or on the untreated Si(100) surface. It is postulated that a 3-center, 2-electron bonding arrangement, between the adsorbed TMGa and the surface metal dimers on the gallium and aluminum treated Si(lOO) surfaces, allows for facile transfer of methyl groups between the adsorbate and the surface metal atoms. The higher methyl-Al bond strength than the methyl-Ga bond strength accounts for the irreversible formation of TMAl on the aluminum treated Si(100). On all of the surfaces, desorption of organometallics dominates over deposition of gallium as TMGa coverage is increased above a monolayer.

Ab initio study on the reaction of trimethylgallium with hydrogen molecule

The reaction of trimethylgallium (Ga(CH 3) 3, TMG) with H 2 has been investigated using ab initio molecular orbital calculations. It has been shown that the activation energy of the reaction TMG+H 2→GaH(CH 3) 2+CH 4 is 34.2 kcal/mol, while the dissociation energy of the radial decomposition TMG→Ga(CH 3) 2+CH 3 is 76.9 kcal/mol. This means that TMG decomposition is dominated by hydrogenolysis under the conditions where collisions between TMG and H 2 are sufficiently frequent. This result explains the experimental result that the decomposition of TMG was enhanced by increasing the H 2 pressure.

Trimethylgallium based phosphinogallanes. Synthesis and molecular structure of [Me 2Ga-P(SiMe 3) 2] 2

The sterically demanding phosphinogallane [Me 2Ga- P(SiMe 3) 2] 2, prepared from reaction of trimethylgallium and tris(trimethylsilyl)phosphine in toluene, has been characterized by partial elemental analyses, 1H NMR and single crystal X-ray diffraction. The title compound crystallizes in the space group P 1 (No. 2) with unit cell dimensions α=9.711(1), β=9.857(1), χ=9.2t1(1) Å, α=99.62(1), β=116.25(1), γ=76.28(1)°, V=766.3, Å 3 and D calc=1.20 g cm −1 for Z=1. Refinement converged at R=0.037, R w=0.046, based on 1606 observed reflections with intensities I>3σ( I). The independent GaP distance was determined to be 2.456(1) Å. Pyrolysis of the dimer did not afford higher order phosphinogallanes.

In‐Situ mechanistic studies of the reaction of trimethylgallium and phosphine in zeolite H‐Y

AbstractCoherent anti‐Stokes Raman scattering (CARS) has been utilised to monitor the decomposition of trimethylgallium (TMGa) on the reactive internal surface of the protonated form of zeolite Y under metal organic chemical vapour deposition (MOCVD) conditions designed to produce GaP deposits that exhibit quantum‐size effects. The CARS data clearly reveal the facile room temperature decomposition of TMGa in the zeolite, as evidenced by the detection of increasing levels of methane with increasing reaction time. In addition, the zeolite samples were analysed by solid state nuclear magnetic resonance with magic angle spinning (MAS NMR) before reaction, after reaction of TMGa and after subsequent reaction with phosphine at 300°C. These data reveal that TMGa reacts with acid sites in the zeolite 12‐rings, resulting in species containing methyl groups. Subsequent exposure to phosphine removes these methyl group protons, leaving various, as yet not fully characterised, phosphorus species. Exposure to phosphine does not appear to regenerate the acid sites on the zeolite.

Surface reaction mechanisms in GaAs atomic layer epitaxy

The reactions of trimethyl gallium (TMG) on a gallium-rich surface (Ga surface) and an arsenic-rich surface (As surface) of (001)GaAs were studied using quadrupole mass spectrometry (QMS) by temperature programmed desorption (TPD) and the response of desorbed species from the surfaces during the exposure of TMG under a constant temperature. It has been found that TMG is adsorbed and decomposed on both the As and the Ga surfaces in the temperature region where atomic layer epitaxy (ALE) growth can occur. It has also been found that even the decomposed species, i.e. MenGa(n=1, 2), can be desorbed from the Ga surface together with TMG molecules, but not from the As surface. The results are inconsistent with the prevalent model based on selective adsorption on the As surface, and so a new selective desorption model is instead proposed for the self-limiting deposition of Ga for ALE growth. This model emphasizes that even Ga-containing decomposition products, i.e. MenGa(n=1, 2), are desorbed selectively from the Ga surface.

Study of surface reactions in atomic layer epitaxy of GaAs using trimethylgallium by reflectance difference spectroscopy and mass spectroscopy

An in situ real-time study of surface reactions in atomic layer epitaxy (ALE) of GaAs using trimethylgallium (TMGa) by reflectance difference spectroscopy (RDS) and sampled beam mass spectroscopy is reported. These studies reveal several phases in atomic layer epitaxy of GaAs and the self-limiting atomic layer deposition of epilayers using TMGa. The results also lend further support to a proposed reaction kinetics model from a recent RD investigation. The self-limiting mechanism which occurs during TMGa exposure cycles is believed to result from both selective adsorption and reaction of TMGa at As atoms and Ga-vacancy-induced Ga-rich surface reconstructions. It is also shown that strategies for optimal ALE growth of GaAs can be obtained through RD monitoring.

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.

Thermodynamic analysis of the deposition of GaAs epitaxial layers prepared by the MOCVD method

On the basis of a detailed thermodynamic analysis of the Ga-As-C-H system, the initial conditions have been determined, under which the reaction of trimethylgallium (TMGa) and arsine in a hydrogen atmosphere produces a single condensed phase — solid GaAs. Liquid gallium with a small amount of dissolved arsenic is formed simultaneously when the initial ratio of the elements is BVAIII 1, while CH4, GaCH3, GaH and GaH2 are the most abundant if BVAIII < 1. The calculated deposition diagrams are in good qualitative agreement with experimental results published in the literature. A comparison of the calculated composition of the gaseous phase and the results of experiments under the conditions used for the deposition of GaAs epitaxial layers leads to the conclusion that the course and results of the deposition process are significantly affected by transport and kinetic phenomena.

Reflectance-difference spectroscopy study of surface reactions in atomic layer epitaxy of GaAs using trimethylgallium and tertiarybutylarsine

A real-time reflectance-difference spectroscopy (RDS) study of surface reactions of trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) with (001)GaAs surfaces in an ultrahigh vacuum environment is reported. These studies reveal several phases of atomic layer epitaxy of GaAs using TMGa. A model consistent with various kinetics studies is established to explain the distinct behavior observed in RDS during TMGa exposures. It is shown that optimal growth conditions can be achieved through RDS monitoring. The self-limiting mechanism which occurs in TMGa exposure cycle is believed to result from both selective adsorption and reaction of TMGa at As atoms and Ga vacancy induced Ga-rich surface reconstruction. It is also shown that TBAs is a promising arsenic source for atomic layer epitaxy.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

Thermodynamic analysis of the deposition of (Ga, Al)As epitaxial layers prepared by the MOCVD technique

Based on a detailed thermodynamic analysis of the Ga-Al-As-C-H system, starting conditions were determined under with the reaction of trimethylgallium, trimethylaluminium and arsine in hydrogen results in the formation of a single condensed phase, viz. solid (Ga, Al)As. At initial ratios BV/AIII &lt; 1, liquid Ga-Al-As and solid Al4C3 are also formed. At high initial concentrations of the AIII-element alkyl derivatives, solid graphite also emerges, particularly at elevated temperatures and reduced pressures. The calculated composition of the solid (Ga, Al)As is compared with experimental data.

The Mechanisms and Kinetics of Surface Reactions of Trimethylgallium on GaAs (001) Surfaces and Its Relevance to Atomic Layer Epitaxy

ABSTRACTX-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction (RHEED) have been applied to study the stable adsorbed Ga species and surface structures after GaAs (001) 2 × 4 As-rich surfaces are exposed to TMGa. These studies show that Ga atoms are the final adsorbed species, that Ga deposition is saturated at one atomic layer at temperatures between 360 and 530 °C and that the surface converts from a 2 × 4 to a 4 × 6 reconstruction after TMGa adsorption. To understand the surface reaction kinetics involved, reflectance-difference spectroscopy (RDS), an in situ rea-ltime optical technique developed by Aspnes et al., is applied to investigate TMGa adsorption on (001) GaAs surfaces. The kinetics of the surface reactions and reconstructions have been characterized over the temperature range from 400 to 500 °C using RDS. The transient RDS behaviors are interpreted by the application of a model that involves selective adsorption and reaction of TMGa at surface As sites and at Ga vacancies on Ga-rich reconstructed surfaces. Based upon these interpretations, rates of reaction and by product desorption are determined that suggest optimal strategies for ALE growth of GaAs.

Ftir Studies Of Organometallic Surface Chemistry Relevant To Atomic Layer Epitaxy.

ABSTRACTThe adsorption and surface reactions of trimethylgallium and tertiarybutylarsine on GaAs(100) surfaces have been investigated by Fourier transform infrared spectroscopy. Adsorbed methyl groups resulting from the dissociative chemisorption of trimethylgallium on GaAs(100) are shown to form As-H and CH2 species on the surface. The CH2 groups are stable on the surface at temperatures as high as 550 °C. The surface coverage is low (∼0.2% of a monolayer) and is reduced by the presence of hydrogen on the surface. This dehydrogenation of surface methyl groups could be a possible route to carbon incorporation in GaAs grown by atomic layer epitaxy. Tertiarybutylarsine is shown to decompose primarily by homolysis to form a tertiary butylgroup and AsH2. At temperatures below 400°C on trimethylgallium dosed surfaces, the decomposition products appear to cause the hydrogenation of methylene groups remaining from prior surface dosing with trimethylaallium. At high temperatures, the tertiarybutyl radical appears to undergo dehydrogenation reactions to an unsaturated species which is stable on the surface. In contrast, the dehydrogenation does not appear to occur on surfaces treated with tertiarybutylarsine. The data for trimethylgallium and tertiarybutylarsine support the general assertion that surface As-H species play a critical role in the removal of hydrocarbon species from the growth surface.

Organogallium chemistry of macrocyclic amines. Synthesis and molecular structure of [Ga(CH3)3]4[(CH3)4[14]aneN4] and [Ga(CH3]2[14]aneN4[Ga(CH3)3

Abstract Reaction of trimethylgallium with the tetradentate macrocyclic amine [(CH3)4[14]aneN4] in toluene affords the crystalline adduct product [Ga(CH3)3]4-[(CH3)4[14]aneN4], I. I crystallizes in the orthorhombic space group Pbca (No. 61) with unit cell parameters a = 14.002(2), b = 18.542(3), c = 14.477(3) A, V = 3758.6 A3, and Dcalc = 1.26 g cm−3 for Z = 4. Full-matrix least-squares refinement based upon 2222 observed reflections converged at R = 0.039 (Rw = 0.060). Due to the four trimethylgallium units the macrocycle in I has been forced to assume an exodentate conformation. I resides about a crystallographic center of symmetry with independent GaN bond distances of 2.182(4) and 2.202(4) A. The crystalline product [Ga(CH3)]2[14]aneN4[Ga(CH3)3]2, II, isolated from reaction of trimethyl-gallium with [14]aneN4 in toluene, crystallizes in the triclinic space group P 1 (No. 2) with unit cell parameters a = 8.016(4), b = 9.437(3), c = 9.669(3) A, α = 75.53(3), β = 67.80(4), γ = 73.26(4)°, V = 640.2 A3, and Dcalc = 1.54 g cm−3 for Z = 1. Full-matrix least-squares refinement based upon 1694 observed reflections converged at R = 0.042 (Rw = 0.059). II resides about a crystallographic center of symmetry with a planar Ga2N2 four-membered ring occupying the central cavity of the macrocycle. The Ga2N2 ring has a mean GaN bond distance of 2.009(6) A. The GaNGa bond angle in the Ga2N2 ring is 90.2(2)° while the NGaN bond angle is 89.8(2)°. The ··· Ga contact of 2.847(1) A does not suggest significant metal-metal interaction. The GaN distances in I and II are among the longest reported.

Surface Chemistry of CVD Reactions Studied by Molecular Beam/Surface Scattering

ABSTRACTA molecular beam/surface scattering experiment in an ultrahigh vacuum is conceptually a simulation of a CVD reactor without the interference from gas phase and wall reactions. The surface chemistry can be studied in real-time during the deposition reaction at the desired temperature. In our experiment, we used pulsed molecular beams of the reactants and a mass spectrometer to monitor In real-time the reaction products evolving from the substrate surface. With this arrangement, the reaction probability of the molecules can readily be determined by measuring the unreacted fraction of the molecular beam. The reaction pathways can be deduced from the Identification of the reaction products, while their time-evolutions give the kinetic parameters. We shall illustrate this technique by our study on the reactions of trimethylgallium and triethylgallium on GaAs as related to the metalorganic CVD and atomic layer epitaxy of GaAs.

Kinetic limits to growth on (001) and (110) GaAs by OMCVD

This paper summarizes results of our investigations of growth on (001) and (110) GaAs by atmospheric pressure organometallic chemical vapor deposition (OMCVD). We follow evolutions of surface species to a sensitivity of 0.01 monolayer (ML) on a time scale of 0.1 s under alternating flows of trimethylgallium (TMG) and arsine (AsH 3) as functions of partial pressure, sample temperature, and surface orientation. The reaction of TMG with an AsH 3-saturated (001) surface is rate-limited by competition between desorption and decomposition of TMG molecules chemisorbed to surface lattice sites via an exclude-volume mechanism, while the reaction of AsH 3 with the TMG-saturated (001) surface is essentially instantaneous. In contrast, TMG reacts essentially instantaneously with the AsH 3-saturated (110) surface while the AsH 3 reaction with the TMG-saturated (110) surface is the rate-limiting step. However, the latter rate is not intrinsic to the AsH 3-surface reaction but appears to be determined by desorption of adsorbed species that block active sites.

An experimental and theoretical study of growth in horizontal epitaxial reactors

In this paper we describe an experimental and theoretical study of the effects of susceptor slope and natural convection on the growth rate in horizontal epitaxial reactors. A mathematical model for mass, momentum and energy transfer was developed for this purpose. The growth of gallium arsenide by the reaction of trimethylgallium and arsine gas in hydrogen was used as the experimental vehicle for this study. The growth rates predicted by this model were compared with experimental data for reactor pressures from 76–760 Torr and for susceptor slopes spanning the range from conventional low angle (7°) to near stagnation flow geometries (81°). Excellent correlation between modeled and experimental results was demonstrated over this range of susceptor slopes, with no adjustable parameters. Natural convection effects were found to dominate at higher reactor pressure and steeper susceptor slopes. Growth rate uniformity and growth efficiency issues are also discussed in this paper. It is shown that, for the reactor geometry considered here, the usable area growth efficiency is maximized for susceptor slopes around 5°. However, optimization of this parameter is not of itself sufficient, since material quality considerations necessitate operation at pressures where recirculation effects are absent.

Growth of GaN single crystal films using electron cyclotron resonance plasma excited metalorganic vapor phase epitaxy

A low-temperature growth technique for GaN single crystal films has been developed utilizing electron cyclotron resonance (ECR) plasma excitation. The GaN film has been grown in a low pressure metalorganic vapor phase epitaxy (MOVPE) system using the reaction of trimethylgallium with highly activated nitrogen extracted from the ECR plasma chamber. Growth conditions of GaN single crystal films have been clarified by examining reflection high-energy electron diffraction patterns. The surface morphology of the GaN single crystal film is very smooth and electrical properties are comparable to those of a MOVPE technique at high growth temperatures.

Device Quality Polycrystalline Gallium Arsenide on Germanium/Molybdenum Substrates

This paper describes the growth of polycrystalline films of gallium arsenide on molybdenum substrates with an intermediate layer of germanium. The gallium arsenide layer is grown by the reaction of trimethylgallium and arsine in a cold‐wall reactor system. Germanium layers are formed by vacuum evaporation, as well as by the pyrolysis of germane gas. Techniques are described for minimizing massive autodoping effects which are commonly observed in the heteroepitaxy of these semiconductors. Doping concentrations in the range of are obtained for the gallium arsenide film. Schottky diodes, fabricated in this material, exhibit avalanche breakdown in the range of 30–35V.

The Effect of Chloride Etching on GaAs Epitaxy Using TMG and AsH3

A study has been made of the effect of in situ etching of (100) Cr‐doped semi‐insulating and Te‐doped substrates on epitaxial layers, grown by the reaction of trimethylgallium and arsine. It is shown that in situ etching enables the growth rate to be increased by a factor of two while retaining a specular surface. In addition, the Hall mobility is higher in epitaxial layers grown on in situ etched substrates than on unetched ones. Epitaxial films on both and gas‐etched substrates had a room temperature mobility that decreased from ≃6100 cm2/V‐sec in 5.5 μm layers to ≃5100 cm2/V‐sec in 1 μm layers. However, for layers grown on substrates which were not in situ etched, the mobility decreased from ≃5800 to ≃3800 cm2/V‐sec for layer thicknesses from 5.5 to 1 μm, respectively. Further it is shown that the carrier concentration profile is more abrupt near the epitaxial layer/Te‐doped substrate interface when the substrates were in situ etched. Finally, experiments with chloride etching during growth were disappointing because it was not possible to obtain simultaneously good surface morphology, low carrier concentration, and high mobility for any given set of reactor conditions.