4H-SiC epitaxial layers have been grown using trichlorosilane (TCS) as the silicon precursor source together with ethylene as the carbon precursor source. A higher C/Si ratio is necessary compared with the silane/ethylene system. This ratio has to be reduced especially at higher Si/H2 ratio because the step-bunching effect occurs. From the comparison with the process that uses silane as the silicon precursor, a 15% higher growth rate has been found using TCS (trichlorosilane) at the same Si/H2 ratio. Furthermore, in the TCS process, the presence of chlorine, that reduces the possibility of silicon droplet formation, allows to use a high Si/H2 ratio and then to reach high growth rates (16 *m/h). The obtained results on the growth rates, the surface roughness and the crystal quality are very promising.

The growth rate of 4H-SiC epi layers has been increased by a factor 3 (up to 18μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.

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The Multijunction (MJ) monolithic approach is very attractive for a competitive concentrating photovoltaic (CPV) technology; it has been successfully applied for InGaP/GaInAs/Ge triple-junction structures but it is more difficult to be exploited for manufacturing 4-junction solar cells, in particular when III-V and IV elements are both used. So far, the integration of the 1 eV SiGeSn material in the lattice-matched InGaP/GaInAs/Ge triple-junction structure has required the utilization of two different growth apparatus, nearly losing the economic advantage of the monolithic architecture, owing to the related higher capital expenditure. The central technical challenge for realizing InGaP/GaInAs/SiGeSn/Ge solar cell at low cost, with an industrial approach, lies in the growth of III-V and IV elements in the same MOVPE equipment, by solving the "cross contamination" problem among the III-V elements and the IV elements. In this contribution, for the first time, the results of the investigation concerning the growth of SiGe(Sn) and III-V compounds in the same MOVPE growth chamber are presented. The epitaxial layers have been characterized by XRD, SEM, TEM, EDX, SIMS and ECV profiling. It is eventually shown that by starting from a modification of the MOVPE equipment and by setting up proper growth condition the contamination of III-V elements in IV based materials can be drastically reduced from 10 20 cm-3 to 2*10 17 cm-3 , while the contamination of IV elements in III-V compounds can be reduced from 4-5*10 17 cm-3 to 6*10 16-3*10 14 cm-3 depending on the substrate used.

New approaches to MOVPE material deposition have been developed in order to increase the process yield and expand the band gap engineering possibilities for the realization of high efficiency multijunction (MJ) solar cells. Paradigm changes in the MOVPE growth chamber design have been introduced in order to maintain high thermal homogeneity at the wafer surface also in the case of the growth of strained structures and to allow getting a fast temperature control at the interfaces between arsenide and phosphide materials. Furthermore, the growth chamber design has been modified in order to remove the growth incompatibility among III-V and group IV elements of the period table. A significant step ahead has been accomplished in reducing the cross doping effects coming from the utilization of the different semiconductor materials, thus opening the path towards the realization of "all MOVPE grown" III-V/IV based MJ solar cells (like for example the InGaP/InGaAs/SiGeSn/Ge quadruple junction solar cells). As a proof of the concept, SiGe layers with high structural quality have been grown in the same MOVPE reactor used to growth InGaP/InGaAs/Ge MJ solar cell structures and a first demonstration of a properly working InGaP/InGaAs/SiGe/Ge TJ solar cell is presented.