| Summary: | This project focuses on the investigation of Silicon based Tandem solar cell fabricated by using the Hydride Vapor Phase Epitaxy (HVPE). In the state-of-the-art multi-junction solar cell manufacturing epitaxial technologies are used for sub-cell formation, such as MOVPE (Metal Organic Vapour Phase Epitaxy) [1] or MBE (Molecular Beam Epitaxy) [2]. Tandem solar cell structures consist of subcells made of III-V semiconductors serially connected or grown on a suitable semiconductor substrate [3]. The used semiconductor materials have to be lattice matched to each other and with optimum band gap combinations [4]. Multi-junction solar cells with Si and III-V semiconductor sub-cells are promising to achieve extremely high efficiency. The objective of this project is to investigate a cost effective fabrication technology to realize III-V semiconductor and silicon based sub-cells in tandem solar cells. The Si p-n junction formation by PH3 diffusion for the silicon sub cell is studied in HVPE. A prototype InP solar cell was fabricated by HVPE and its I-V performance was studied. In this thesis, the impact of HVPE process parameters on the silicon p-n junction formation was examined by alternating the process temperature. Silicon samples were processed in the HVPE with temperature values of 1st (605 0C) < 2nd (657 0C) < 3rd (720 0C). It is observed that the temperature affects the quality of the formed Si p-n junction. The Si samples treated at 720 0C show a diode performance with a deviated I-V curve due to parasitic resistances. The InP solar cell fabrication consisted of the epitaxial growth of sulfur doped n-InP and zinc doped p-InP materials on top of each other to form n+/n+/n-/p+ [5] structure. Ohmic conduction through the InP solar cell structure was observed after the contacts formation, which could be due to the metal alloy spiking through the p-InP emitter layer during annealing. Process mitigations to fabricate InP solar cell by HVPE are proposed at the end of project.
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