Local Isolation of High-Voltage Photovoltaic Cells Using Buried Layers of Oxidized Porous Silicon

In this paper, we have developed a simple method to isolate epitaxially grown thin silicon film using micrometer thick layers of buried porous silicon. The process is based on formation of trenches within epitaxial p-type Si layer that was grown on top of a p⁺-type Si (100) wafer. Either electrochemical or galvanic etching in hydro-fluoric solutions procedures were employed to etch the p⁺-type silicon under and around the trenches, at the interface of the substrate and the epi-layer, and to transform the etched material into buried PSi. Electrical characteristics of the formed isolation, called 'local isolation by buried oxidized PSi', have been measured. The isolation resistance of the subsequently oxidized PSi film was found to increase by 3-6 orders of magnitude up to the level of few GΩ (GigaOhms). Finally, this procedure has been exploited to demonstrate a miniature photovoltaic solar array where two photovoltaic cells were connected in series using the laser-induced forward transfer metallization process, as a model for high voltage photovoltaic solar cell.