Decomposition Of Trimethylgallium Research Articles

Gas Phase Reactions in Horizontal MOCVD Reactors

ABSTRACTWe have applied kinetic simulation to MOCVD chemistry in a horizontal MOCVD reactor. Both chemical reactions and material diffusion are considered. For trimethylgallium decomposition, concentrations of chemical species reach their steady state values which differ largely from the equilibrium values.

Multiphoton-ionization / mass spectrometric detection of gallium atom during the trimethylgallium CVD reaction

Gallium atoms were detected by multiphoton-ionization mass spectrometry in the low-pressure decomposition of trimethylgallium (TMG) on heated substrates (300–1100K). On copper surfaces, an activation energy of 34±3 kcal mol −1 was found for the production of Ga (ground state). This activation energy is attributed to the desorption of gallium from the surface. GaAs substrates produce similar results at lower temperatures ( T⩽ 870 K).

Stepwise monolayer growth of GaAs by switched laser metalorganic vapor phase epitaxy

Growth of GaAs by repeated deposition of single atomic layers using the switched laser metalorganic vapor phase epitaxy technique is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for stepwise epitaxy—the ideal atomic layer epitaxy. This is achieved by suppressing pyrolytic decomposition and favoring photocatalytic decomposition of trimethylgallium (TMG). A growth model for stepwise monolayer epitaxy is proposed which suggests that photocatalytic decomposition of TMG occurs only at surface As atoms and not at Ga atoms.

Homogeneous and heterogeneous thermal decomposition rates of trimethylgallium and arsine and their relevance to the growth of GaAs by MOCVD

The rate of decomposition of trimethylgallium (TMGa) and arsine is measured by sampled gas infrared absorption spectroscopy. The decomposition of TMGa is observed to go to completion at temperatures above 475°C as measured by the concentration of CH 4 that is formed in the decomposition process. An activation energy of 58–62 kcal/mol is measured for the loss of the first methyl group. The decomposition of arsine is characterized by strong surface interactions. The activation energy for the decomposition of arsine in a quartz vessel is 34 kcal/mol. The activation energy for decomposition of AsH 3 in the presence of GaAs wafers was found to be 18 kcal/mol. The implications of these results for the growth of GaAs by metalorganic chemical vapor deposition (MOCVD) are discussed.

Gas phase depletion and flow dynamics in horizontal MOCVD reactors

Growth rates of GaAs in the MOCVD process have been studied as a function of both lateral and axial position in horizontal reactor cells with rectangular cross-sections. A model to describe growth rates in laminar flow systems on the basis of concentration profiles under diffusion controlled conditions has been developed. The derivation of the growth rate equations includes the definition of an entrance length for the concentration profile to developed. In this region, growth rates appear to decrease with the 1/3 power of the axial position. Beyond this region, an exponential decrease is found. For low Rayleigh number conditions, the present experimental results show a very satisfactory agreement with the model without parameter fitting for both rectangular and tapered cells, and with both H 2 and N 2 as carrier gases. Theory also predicts that uniform deposition can be obtained over large areas in the flow direction for tapered cells, which has indeed been achieved experimentally. The influence of top-cooling in the present MOCVD system has been considered in more detail. From the experimental results, conclusions could be drawn concerning the flow characteristics. For low Rayleigh numbers (present study ≲ 700) it follows that growth rate distributions correspond with forced laminar flow characteristics. For relatively high Rayleigh numbers (present work 1700–2800), free convective effects with vortex formation are important. These conclusions are not specific for the present system, but apply to horizontal cold-wall reactors in general. On the basis of the present observations, recommendations for a cell design to obtain large area homogeneous deposition have been formulated. In addition, this work supports the conclusion that the final decomposition of trimethylgallium in the MOCVD process mainly takes place at the hot substrate and susceptor and not in the gas phase.

Mass Spectrometric Study of Ga ( CH 3 ) 3 and Ga ( C 2 H 5 ) 3 Decomposition Reaction in H 2 and N 2

Decomposition of trimethylgallium (TMG) and triethylgallium (TEG) in hydrogen and nitrogen atmospheres was studied by a quadrupole mass analyzer. The decomposition reactions of TMG in and in and of TEG in and in take place in the temperature ranges 370°–460°, 450°–570°, 220°–330°, and 270°–380°C, respectively. The reaction mechanisms are hydrogenolysis for TMG in , homolytic fission for TMG in , and β elimination for TEG in both and . The hydrogenolysis of TMG follows homogeneous first‐order kinetics on TMG concentration.

MPI/MS Studies of Thin Film Deposition Processes: Methyl Production from Trimethylgallium Decomposition and the Effect of Added Hydrazine

ABSTRACTThe low pressure pyrolysis of alkylmetals on resistively heated substrates was studied using multiphoton and electron ionization mass analysis. The activation energy for the production of gas phase methyl radicals from the decomposition of trimethylgallium under single collision conditions was found to be 26 ± 3 kcal/mol, which is to be compared to 13 ± 2 kcal/mol previously observed for trimethylaluminum. No evidence could be found for any surface radical reactions leading to the production of CH4 or C2H6. A proposed deposition mechanism accounting for these observations was tested by pyrolyzing trimethylgallium in the presence of hydrazine. No change in methyl signal was observed, supporting the theory that radical reactions do not occur on the surface under the conditions employed.

Interface reactions and grain growth processes in poly-GaAs deposited on molybdenum substrates by the organometallic process

This paper describes grain growth processes for polycrystalline gallium arsenide on molybdenum substrates. Growth was carried out by the pyrolytic decomposition of trimethylgallium and arsine in hydrogen. The ability of the organometallic process to allow the growth of gallium arsenide over a wide temperature range is exploited in the initial nucleation and growth phase to obtain full coverage of the substrate. A heat treatment step is used to provide grain expansion and results in a surface with a rippled character. We propose that this comes about by the dissociation of GaAs at the interface, due to strong Mo-As reactions at the annealing temperature, resulting in regrowth of GaAs from a liquid-like phase. Eventual growth of a device quality, active layer is accomplished by conventional CVD growth at 650–700°C, resulting in an average grain size of 6 μm for a 6–7 μm thick overall structure.

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than 5 have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 μm thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

The preparation of device quality gallium phosphide by metal organic chemical vapor deposition

Device quality epitaxial layers of gallium phosphide were grown on gallium phosphide substrates by the decomposition of trimethylgallium (TMG) and phosphine in a hydrogen atmosphere. The lowest background carrier concentration (≈5 × 10 115cm -3) and best surface morphology were obtained at a growth temperature of 800δC and a PH 3/TMG ratio ≈10 for a growth rate of 0.17 μm/min. The layers can be controllably doped n- or p-type by the use of hydrogen selenide or diethylzinc. Both n-and p-type material with mobilities of ≈120 cm 2/V · s and carrier concentrations of ≈10 16 cm -3 can be prepared. Rectifying diodes with reverse leakage currents of <10 μA at 120 V were grown.