A model for the surface chemical kinetics of GaAs deposition by chemical-beam epitaxy

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Abstract
Recently we have reported the measurement of reflection high‐energy electron diffraction intensity oscillations during chemical‐beam epitaxy of GaAs using triethylgallium (TEG) and As2 derived from an arsine cracker [Appl. Phys. Lett. 5 0, 19 (1987)]. In this study we observed a significant variation of the GaAs growth rate with substrate temperature at constant TEG flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be nonlinear below approximately 500 °C and linear above 500 °C for incident fluxes yielding maximum growth rates between 0.2 and 1.8 monolayers/s. We have developed a model of the surface pyrolysis of triethylgallium which explains the qualitative behavior of the above data. The model assumes the existence of adsorbed triethyl, diethyl, and monoethyl gallium species as well as adsorbed ethyl radicals. As a starting point, the rate limiting step to epitaxial incorporation of atomic gallium is assumed to be cleavage of the second ethyl–gallium bond. Elimination of atomic hydrogen from adsorbed ethyl groups to form ethylene is also included in the model, as is recombination of one ethyl group and a diethylgallium to form adsorbed triethylgallium. Assuming Arrhenius behavior for the rate constants of the elementary steps of the reaction mechanism and steady‐state behavior an expression for the temperature dependence of the growth rate is derived. Using realistic values for the preexponential factors and activation energies of the elementary steps a reasonable fit to the experimental data was obtained. The model reproduces the nonlinear dependence of growth rate on incident flux below 500 °C and the fall‐off growth rate at higher temperature. The nonlinearity is due to the second‐order recombination of an adsorbed diethyl gallium radical with an adsorbed ethyl radical followed by desorption of triethylgallium. The fall‐off in growth rate above 500 °C is due to desorption of diethyl gallium radicals.