Computational Investigation of Selective MOVPE of Al x Ga 1-x As in Presence of HCl
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COMPUTATIONAL INVESTIGATION OF SELECTIVE MOVPE OF AlXGa1-XAs IN PRESENCE OF HCl Maria Nemirovskaya, Carlo Cavallotti, and Klavs Jensen Dept. Chemical Engineering, Massachusetts Institute of Technology 77 Massachusetts Ave., Cambridge, MA 02139, U.S.A. ABSTRACT The deposition of AlGaAs in the presence of HCl was investigated at the macroscopic and mesoscopic scales. Fluid dynamics simulations were first performed in order to study the dependence of the deposition rate on the operating conditions. Unknown gas phase and surface kinetic parameters were estimated by quantum chemistry and transition state computations. The fluxes of all species to the surface were thus computed and provided the input to a kinetic Monte Carlo model used to investigate the morphology evolution of the film. INTRODUCTION MOVPE of AlGaAs is an important step in production of electronic and opto-electronic devices such as high performance transistors, lasers and light emitting diodes. Selective epitaxy offers significant savings by eliminating some of the manufacturing steps. For AlGaAs films selectivity is achieved by adding HCl. Fabrication of small high quality devices creates a need for understanding and being able to predict physical processes taking place in MOVPE system. In this work we aim to simulate film growth rate and morphology as a function of operating conditions. The strategy is to develop a reactor scale (macroscopic) model and a surface (mesoscopic) model. On the reactor scale, we investigate macroscopic film growth rate and composition as well as obtain boundary conditions for the surface model. The surface model provides information about film morphology and surface fluxes. Gas phase and surface reactions kinetic constants and surface diffusion barriers for AlGaAs are the most important parameters. They are either obtained from the literature or calculated through quantum chemistry when unknown. The paper is organized as follows: first, quantum chemistry calculations and kinetic mechanism for growth or etching of GaAs in the presence of HCl are discussed. Then, we present reactor scale simulations results and compare them with the experiments. Finally, we describe the surface model for selective epitaxy of AlGaAs. KINETIC MECHANISM The simulation of growth and etching of AlGaAs films over a wide range of operating conditions requires the use of a detailed kinetic scheme consisting of gas-phase and surface reactions. The mechanism proposed here summarizes the extensive knowledge that has been developed in many years of experimental and theoretical investigation on the GaAs growth chemistry. Kinetic constants of most gas-phase and surface reactions are reported in the literature. The kinetic constants involving HCl are not known and are calculated using quantum chemistry. The kinetic constants of more than 60 gas phase reactions involving HCl and Ga or Al precursors were determined with the B3LYP method and the 6-311+g(d,p) basis set [1]. Then T3.4.1
sensitivity analysis was performed and the most important reactions were id
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