ISSN 1063-7842, Technical Physics, 2008, Vol. 53, No. 12, pp. 1602–1605. © Pleiades Publishing, Ltd., 2008. Original Russian Text © S.A. Smirnov, V.N. Panteleev, Yu.V. Zhilyaev, S.N. Rodin, A.S. Segal, Yu.N. Makarov, A.V. Butashin, 2008, published in Zhurnal Tekhnicheskoœ Fiziki, 2008, Vol. 78, No. 12, pp. 70–73. 1602 INTRODUCTION Growth of gallium nitride (GaN) epitaxial layers on sapphire substrates is of interest for production of high- power short-wavelength light-emitting and laser diodes. Chloride epitaxy is today viewed as a promising method for obtaining such layers, because it allows growth of high-quality layers with a growth rate vary- ing typically from 5 to 500 μm/h (see, e.g. [1]). A prob- lem that has to be solved in designing the reactor is pro- vision of uniform distribution of the growth rate over the substrate. To a certain extent, this problem can be solved by rotating the substrate about its axis. However, experiments show that rotation alone may not suffice to solve this problem completely, because it does not eliminate the radial nonuniformity of the growth rate. In this work, we analyze the reasons for the nonuni- form distribution of GaN growth rate over the substrate by numerically simulating chloride epitaxy of GaN in a horizontal reactor. As a basis, we took a steady-state 3D model of the process that takes into account the flow under gravity of a nonisothermal viscous mixture com- prising GaCl, NH 3 , Ar, HCl, and H 2 ; conductive, con- vective, and radiative heat exchange; and heteroge- neous reactions on the substrate and reactor walls. Recently, this model has been verified by contrasting related results with experimental data obtained by dif- ferent authors [2] and has been used to simulate chlo- ride epitaxy of GaN in a vertical reactor [3]. Simulations have shown a strong influence of the gas diffusion on the distribution of the polycrystalline GaN growth rate over the reactor walls. In particular, ammonia has been found to diffuse a large distance in the direction opposite that of the main gas flux. As a result, the deposit grows on the reactor elements upstream of the ammonia inlet. It has also been found that the growth of polycrys- talline GaN deposit on the reactor walls considerably depletes the gas mixture in GaCl above the near-wall periphery of the substrate, rendering the growth rate distribution over the substrate more nonuniform. This effect can be eliminated by increasing the diameter of the reactor. It is demonstrated that the simulated and experimental distributions of the GaN growth rate over the substrate and reactor walls are in good agreement. MATHEMATICAL MODEL A model of GaN chloride epitaxy used in this paper includes the Navier–Stokes equations of the viscous nonisothermal gas-mixture dynamics and the equations of material (component), heat, and radiation transfer that are conjugate with the kinetic equations for hetero- geneous chemical reactions [1, 2]. Direct mass-spectro- metric studies [4] and thermodynamic analysis [5] show that GaCl, NH 3 , HCl, H 2 , and N 2 are the main components in the gas system of interest. Other compo- nents are present in a negligibly small amount. The HCl Growth of Single-Crystalline GaN Layers in a Horizontal Reactor by Chloride Epitaxy S. A. Smirnov a , V. N. Panteleev b , Yu. V. Zhilyaev b , S. N. Rodin b , A. S. Segal c , Yu. N. Makarov d , and A. V. Butashin e a OOO Gallii-N, St. Petersburg, 194156 Russia e-mail: ssmirnov@softimpact.ru b Ioffe Physico-Technical Institute, Russian Academy of Science, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia c OOO Soft-Impact, St. Petersburg, 194156 Russia d OOO Nitridnye Kristally, St. Petersburg, 194156 Russia e Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia Received November 22, 2007 Abstract—Chloride epitaxy of GaN layers in a horizontal reactor is studied numerically. The steady 3D fluxes of the gas mixture in the reactor are simulated with allowance for heterogeneous reactions on the substrate (growth of epitaxial GaN layers) and on the reactor walls (growth of a polycrystalline GaN deposit). Experi- mental data on the growth rate distribution for polycrystalline and epitaxial GaN layers are explained. It is shown that, if the diameter of the reactor is not large enough, the growth of the deposit on the walls makes the GaN growth rate distribution over the substrate more nonuniform due to the parasitic diffusion of reagents from the gas phase to the reactor walls. PACS numbers: 81.10.-h DOI: 10.1134/S1063784208120116 SOLID-STATE ELECTRONICS