Istituto dei materiali per l'elettronica ed il magnetismo     
Bosi M., Attolini G., Calicchio M., Ferrari C., Frigeri C., Gombia E. Homoepitaxial growth of germanium for photovoltaic and thermophotovoltaic applications. In: ICCG-16 - ICCG-16, The 16th International Conference on Crystal Growth (Beijing (Cina), 8-13 Aug. 2010). Abstract, p. 08/09. Chinese Academy of Sciences, 2010.
Low bandgap Ge homojunctions are normally used in photovoltaic multiple junction solar cells or thermo-photovoltaic cells and are usually realized by thermal diffusion, starting from an n-type or p-type substrate. However the diffusion process itself intrinsically precludes the possibility to obtain sharp junctions and to control the doping profile. A better thickness and doping control could be achieved by epitaxial deposition of Ge junctions, with the aim to obtain better photovoltaic efficencies. Single junction epitaxial Ge cells with high efficiency could find use either in III-V multijunction high efficiency solar cells or in thermophotovoltaic devices coupled to a burner and to suitable selective emitters based on rare earth elements. In the present work homoepitaxial Ge layers were deposited by means of Metal Organic Vapur Phase Epitaxy (MOVPE) on Ge using Iso-Butyl Germane (iBuGe) as organic precursor. Structures of different thickness were growth by varying the deposition temperature between 550 and 700C on n and p-type Ge substrates. The layers were found to be intrisically doped p-type with high carrier concentration. By using AsH3 it was possible to achieve n-type doping. X-Ray diffraction and Transmission Electron Microscopy confirmed the good crystallographic quality of the layers. By depositing a p-type layer onto an n-type Ge substrate or, viceversa, an n-type layer on a p-type Ge substrate is was possible to realize p/n (or n/p) junctions. A totally epitaxial Ge n/p structure was also deposited onto a p-type substrate. Mesa structures were realized in order to perform electrical I-V and C-V characterization on the junctions. The junctions were characterized by means of a solar simulator (AM1.5, 0.7 suns) to measure the photovoltaic conversion efficiency, and by photocurrent to get the spectral behaviour of the cells.
Subject Ge/Ge

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