CELL STRUCTURES BY 3-DIMENSIONAL GRAPHOEPITAXY ON METAL MIRRORS

SPIRE PROPOSES AN INNOVATIVE APPROACH TO MINIMIZE THE COST AND TO MAXIMIZE THE EFFICIENCY OF SILICON SOLAR CELLS BY UTILIZING THIN-FILM LIMIT-EFFICIENCY (27% AM1) DESIGN CONCEPTS. SPECIFICALLY, IT PROPOSES TO DEMONSTRATE THE FEASIBILITY OF FABRICATING ESSENTIALLY SINGLE-CRYSTAL SILICON FILMS WITH BACK-SURFACE MIRRORS FOR OPTICAL CONFINEMENT BY MEANS OF THREE-DIMENSIONAL GRAPHOEPITAXY. THE APPROACH COMPRISES THREE STEPS. FIRST, SURFACE RELIEF STRUCTURES COMPATIBLE BOTH WITH THE STABLE, OCTAHEDRAL GROWTH MORPHOLOGY AND THE (100) FILM ORIENTATION ARE TO BE REPLICATED BY DEPOSITING REFRACTORY METAL FILMS UPON TEXTUREETCHED (100) SILICON SURFACES. THIS CIRCUMVENTS BOTH THE HIGH COST AND THE GEOMETRIC LIMITATIONS OF THE PHOTOLITHOGRAPHICALLY DEFINED 1- AND 2-DIMENSIONAL GRATINGS NOW USED. THE SECOND STEP IS THE DEPOSITION OF SILICON FILMS UPON THE METAL REPLICATES, FOLLOWED BY THE DEPOSITION OF PROTECTIVE OXIDE/NITRIDE OVERLAYERS. THIRD, THE AS-DEPOSITED SILICON FILMS ARE TO BE CRYSTALLIZED BY SCANNEDSTRIP HEATING AND BY PULSED ELECTRON BEAM HEATING. THE CRYSTALLOGRAPHICALLY DEFINED THREE-DIMENSIONAL RELIEF PROVIDED BY THE METAL REPLICATE IS EXPECTED TO INDUCE TRUE SINGLE-CRYSTALLINITY, RATHER THAN THE LARGE-GRAIN CRYSTAL MOSAICS OBTAINED TO DATE. EQUALLY AS IMPORTANT, THE METAL REPLICATE REMAINS AS AN INTEGRAL FACETED BACK-SURFACE MIRRORTO BE USED FOR OPTICAL CONFINEMENT.