Journal of Crystal Growth 223 (2001) 15–20 On the influence of gas inlet configuration with respect to homogeneity in a horizontal single wafer MOVPE reactor Hilde Hardtdegen a, *, Andreas Kaluza a , D. Gauer a , M.v.d. Ahe a , M. Grimm a , P. Kaufmann b , L. Kadinski b a Institut fu ¨r Schicht- und Ionentechnik, Forschungszentrum Ju ¨lich, D-52425 Ju ¨lich, Germany b Lehrstuhl fu ¨r Stro ¨mungsmechanik, Universita ¨t Erlangen-Nu ¨rnberg, Cauerstr.4, D-91058 Erlangen, Germany Received 5 June 2000; accepted 31 October 2000 Communicated by G.B. Stringfellow Abstract In this paper two different gas inlet modifications for a horizontal single-wafer MOVPE reactor were studied: the conventional one ensured gas mixing of groups III and V precursors by forcibly merging both gases in a gas mixing unit, the newer one allowed mixing of groups III and V precursors solely by diffusion after the separation plate. AlAs/ GaAs Bragg reflector structures were deposited in nitrogen atmosphere for both gas inlet types and the uniformity determined by X-ray diffraction. Three-dimensional detailed numerical modeling was employed to explain the results. They establish that the observed strong non-uniformity of growth for the new inlet as well as the unusual concave instead of the common convex growth profile found is due to the incomplete mixing of precursor gases in a highly dense gas phase. By adjusting the groups III/V gas stream ratio an effect could be taken on the diffusion processes. Furthermore the total flow in the reactor was optimized for the new gas inlet. By taking advantage of changed diffusion properties in nitrogen atmosphere, however, perfect uniformity with an absolute deviation smaller than 1% was obtained. The modeling results are presented and agree very well with the experimental data. # 2001 Elsevier Science B.V. All rights reserved. PACS: 81.15.Gh; 02.60.Cb; 81.05.Ea Keywords: A1. 3D numerical simulations; A1. Process optimization; A3. Metalorganic vapor phase epitaxy; B2. Semiconducting aluminum arsenide; B2. Semiconducting gallium arsenide 1. Introduction In the past efforts have been made to increase the layer quality and homogeneity in research scale horizontal MOVPE reactors not only by process but also by equipment optimization. One well- accepted approach [1] was to modify the gas inlet so that the flow of groups V and III source molecules are separated by a platelet until shortly before they reach the substrate surface, injecting the group V sources nearer to the surface than the group III molecules. Three major advantages of this type of gas inlet compared to the conventional *Corresponding author. Tel.: +49-2461-612360; fax: +49- 2461-612940. E-mail address: h.hardtdegen@fz-juelich.de (H. Hardtdegen). 0022-0248/01/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0022-0248(00)00969-6