Istituto dei materiali per l'elettronica ed il magnetismo     
Bosi M., Attolini G., Musayeva N., Arumainathan S., Pelosi C., Ferrari C. Growth and Characterization of Ge Homoepitaxial Structures for Thermo-Fotovoltaic Application by Metal Organic Chemical Vapour Deposition. Rapporto interno n. 114. Technical report, 2007.
Recently, advanced triple junction solar cells based on InGaP/InGaAs/Ge have reached an efficiency value over 40% under concentration. The bottom Ge cell is realised by atomic diffusion in the Ge substrate, and its conversion efficiency is partially limited by the broad doping profile thus obtained. Better photovoltaic performances could be achieved in the long wavelength part of the multi-junction (MJ) solar cell by means of homo-epitaxy of Ge on the Ge substrate, as improved thickness and doping profile control can be obtained with the epitaxial process. Beside the application on triple junction cells, a standalone Ge p-n junction on either GaAs or Ge substrate could be used also as a thermophotovoltaic device and, coupled to an appropriate burner and selective filter, could be used in a co-generation apparatus to provide both heat and electricity. Ge layers were deposited on GaAs and Ge substrates using Metal Organic Vapor Phase Epitaxy (MOVPE) technique and a novel precursor (Iso Butyl Germane - iBuGe) developed by Rohm and Haas. The layer thickness were measured on GaAs using a selective etch and a step profiler. The growth rate dependency on the different growth parameters will be discussed. As was used as a surfactant to improve the surface quality, but it decreases the growth rate. Several growth processes involving As were tested. The samples were observed by optical microscope and characterised by Atomic Force Microscopy (AFM), Raman spectroscopy and X-Ray Diffraction and the relationship between characterisation results and growth parameters will be analysed.
Subject Ge growth

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