A Kinetic Model for Metalorganic Chemical Vapor Deposition of GaAs from Trimethylgallium and Arsine
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A KINETIC MODEL FOR METALORGANIC CHEMICAL VAPOR DEPOSITION OF GaAs FROM TRIMETHYLGALLIUM AND ARSINE TRIANTAFILLOS J.MOUNTZIARIS AND KLAVS F. JENSEN Department of Chemical Engineering and Materials Science University of Minnesota, Minneapolis, MN 55455 ABSTRACT A kinetic model for metalorganic chemical vapor deposition (MOCVD) of GaAs from trimethylgallium and arsine is presented. The proposed mechanism includes 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 29 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Sensitivity analysis and existing experimental observations have been used to develop the reduced mechanism from the large number of reactions that might in principle occur. Rate constants are estimated by using thermochemical methods and reported experimental data. The kinetic mechanism is combined with a two-dimensional transport model of a hot-wall tubular reactor used in experimental studies. Model predictions of gas-phase composition and GaAs growth rates show good agreement with published experimental studies. In addition, the model predicts reported trends in carbon incorporation. INTRODUCTION Metalorganic chemical vapor deposition (MOCVD) has been used successfully to grow a wide variety of III-V and U-VI compound semiconductors on a laboratory scale [1]. However, to obtain uniform layers with controlled impurity incorporation, needed for large scale production of electronic and optical devices, the combined chemical reactions and transport phenomena underlying MOCVD must be understood. Modelling of MOCVD has typically focused on predicting complex flow and heat transfer phenomena for different reactor configurations, while simple overall rate expressions have been used to describe the growth rates [2,3]. Detailed kinetic models must be included in reactor descriptions to go beyond growth rate simulations and to predict film composition and impurity incorporation. As an example of this approach, a kinetic model of silane pyrolysis with mass transfer limited growth of GaAs has been used to simulate Si doping of GaAs from silane and disilane [4]. In this paper we propose a detailed kinetic model for epitaxial growth of GaAs from trimetylgallium (TMG) and arsine (AsH3) to describe kinetically limited growth conditions and carbon incorporation. Although MOCVD of GaAs is perhaps the simplest and most understood compound semiconductor growth process, the development of a kinetic model is a challenging task. The model development is complicated by a large number of gas-phase and surface reactions, incomplete experimental data for gas-phase species, and almost complete lack of mechanistic information and kinetic data for the surface reactions for the various crystallographic orientations. The kinetics of GaAs deposition have recently been addressed through estimates of thermochemical data for intermediate species and equilibrium computations in the gas phase [5] and subsequently by employing finite rate expressions of
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