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the epitaxial silicon deposition is industrially performed by cold wall barrel reactors because their large productivity. Unfortunately, such a high productivity is associated to film thickness control problems. System optimization can be performed satisfactorily only through models where the geometry and the reactor flow dynamics were accounted in detail. Here, the atmospheric Si deposition by SiHCl3/H2mixtures in a AMT 7700 barrel reactor was simulated through of a detailed 2D model solved by the commercial finite element code FIDAP. To obtain a flexible and fast running model to be used on-line, a 1D simplified model was also derived. Different geometrical configurations and deposition conditions were examined, comparing all the simulation with experimental data.

The growth rate of a 4H‐SiC epitaxial layer has been increased by a factor of 19 (up to 112 μm h–1) with respect to the standard process, with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl has been characterized by electrical, optical, and structural characterization methods. The effects of various deposition parameters on the epitaxial growth process have been described, and an explanation of this behavior in terms of the diffusion coefficient on the surface, Ds, and the ratio between the characteristic times, τD:τG, has been provided. The diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process. This process is very promising for high‐power devices with a breakdown voltage of 10 kV.

Different homo epitaxial 4H-SiC commercial wafers were undergone hydrogen etching process that was developed in the reaction chamber of a Hot Wall Chemical Vapor Deposition (HWCVD) reactor. We have studied the effects of physical desorption to point out the morphology and the structural changes of epitaxial surfaces.An optical microscopy inspection was made to trace out a map of defect areas before and after etching treatments. We have analysed the morphological evolution of the surface in every etching process step by means of marked area on the defect map. We also achieved some other important information, concerning structural and morphological changing, by performing Atomic Force Microscopy and Micro Raman spectroscopy analysis on the same defect marked area.The etched epilayers showed a significant reduction of defects density and a good surface morphology. On investigated samples we fabricated Schottky diodes, their electrical behaviour compared to the devices fabricated on not etched epitaxial layer highlights the surface quality improvement and the increasing of SBD working yield. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper we consider the Markov process defined by P1,1=1, Pn,ℓ=(1−λn,ℓ) ·Pn−1,ℓ +λn,ℓ−1 ·Pn−1,ℓ−1 for transition probabilities λn,ℓ=qℓ and λn,ℓ=qn−1. We give closed forms for the distributions and the moments of the underlying random variables. Thereby we observe that the distributions can be easily described in terms of q-Stirling numbers of the second kind. Their occurrence in a purely time dependent Markov process allows a natural approximation for these numbers through the normal distribution. We also show that these Markov processes describe some parameters related to the study of random graphs as well as to the analysis of algorithms.

Unlike conventional antidepressants, rolipram stimulates both the presynaptic as well as the postsynaptic component of monoaminergic transmisson. Several double-blind comparative trials are on the way to assess the clinical efficacy and safety of this novel compound.

Silicon carbide (SiC) is a wide band gap semiconductor, interesting for its physical properties such as high breakdown field, high saturated drift velocity and high thermal conductivity, which has been intensively studied in the last years. Although the high potentiality of this material, the SiC technology shows at the moment some limitations, indeed, the reliability of SiC-based devices is strictly correlated to the defects present in the crystalline structure. 4H-SiC epilayers were grown by Hot Wall Chemical Vapor Deposition (at 1600 °C) and by Sublimation techniques (at 2000 °C). A surface investigation of the epilayers has been performed finding particular physical finger-prints correlated with several kind of defects aimed at giving an important feedback to the epitaxial growth processes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The latest results on 100 mm 2° off and 150 mm SiC-4H epitaxial process using chlorinated chemistry are illustrated in this paper. On 2° off substrates a reduced step-bunching epi surface with a roughness of <0, 27 nm was achieved and the reduction of SSSF and BSSF was also noticed. SiC 150 mm epitaxy process was demonstrated showing an epi thickness dispersion of ± 0.9% and a doping dispersion of ± 9.1%.