Models and Mechanisms of III-V Compound Semiconductor Growth by Movpe
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MODELS AND MECHANISMS OF III-V COMPOUND SEMICONDUCTOR GROWTH BY MOVPE
Klavs F. Jensen, Triantafillos J. Mountziaris and Dimitrios 1.Fotiadis Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis, MN 55455 ABSTRACT
A kinetic model for metalorganic vapor phase epitaxy (MOVPE) of GaAs from trimethylgallium and arsine is imbedded into two-dimensional transport phenomena descriptions of horizontal and vertical MOVPE reactors. The mechanism involves 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 26 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Carbon incorporation is predicted to occur via carbene containing species. A sensitivity analysis shows that only a few reactions are needed to simulate observed growth rates while the full mechanism is important in computing carbon levels in GaAs. The model predictions are in good agreement with data for trimethylgallium decomposition in hot isothermal tubes, with GaAs growth in horizontal reactors, and with carbon incorporation in vertical reactors. The transport-reaction model demonstrates that both gas-phase and surface reactions as well as transport phenomena are important in predicting MOVPE reactor performance. INTRODUCTION Metalorganic vapor phase epitaxy (MOVPE) has become an established technique for growing high purity III-V compound semiconductors for use in optoelectronic devices [1,2]. However, the technique has not yet realized its large scale production potential. Most layered structures are grown in small reactors with 1-3 substrates 50-75 mm wide. Layers of uniform thickness, composition and impurity levels as well as sharp compositional changes between adjacent layers have been achieved in small systems, but these are few (if any) examples of scaleup. To address the uniformity and junction depth issues in large reactors it is essential to understand the transport and chemical reactions of organometallic species underlying the MOVPE process. Transport of energy and mass by diffusion and convection are critical in determining the degree of gas-phase reactions and the access of the film precursors to the growth interface [3]. As the organometallic source compounds approach the hot substrate, they pyrolize to form desirable growth precursors as well as undesirable species leading to carbon incorporation. Similarly, surface reactions lead to growth of the film, but some pathways may also generate unintentional impurities. Spectroscopic investigations of reactant and product species in specially designed reactors have provided new insight into MOVPE gas-phase chemistry in particular for the growth of GaAs from trimethylgallium (TMG) and arsine [4-9]. There is also an increased emphasis on surface chemistry experiments [10-121. The chemistry experiments yield information about the elementary steps of the reaction mechanism which must be consolidated in an overall kinetic model. This has to be included in a transport model for the flow
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