GAAS/A1GAAS HETEROSTRUCTURE POINT-CONTACT CONCENTRATOR CELLS

POINT-CONTACT CELLS FABRICATED IN SILICON HAVE RECENTLY ACHIEVED VERY HIGH EFFICIENCIES. APPLYING THIS STRUCTURE TOGAAS IS DIFFICULT AS IT REQUIRES BOTH SURFACE PASSIVATION OF GAAS AND A FILM OF GAAS WITH THICKNESS LESS THAN TEN MICRONS. WE PROPOSE TO OVERCOME THESE DIFFICULTIES BY (1) USING ALGAAS LAYERS GROWN BY OMCVD TO ACT AS FRONT-AND BACK-SURFACE FIELDS IN ORDER TO CONFINE THE PHOTOGENERATED MINORITY CARRIERS AWAY FROM THE SURFACES, AND (2) USING OUR CLEFT TECHNOLOGY TO PRODUCE THIN, SEPARATED FILMS OF THIS STRUCTURE. EFFICIENCIES OF THE RESULTING CONCENTRATOR CELLSSHOULD EXCEED EXISTING GAAS AND SI CELL EFFICIENCIES. OUR OBJECTIVES FOR PHASE I ARE TO DETERMINE THE OPTIMUM STRUCTURE AND TO PROPOSE THE INITIAL FABRICATION PROCESS FORPOINT-CONTACT GAAS/ALGAAS HETEROSTRUCTURE CONCENTRATOR CELLS. WE WILL DEVELOP A MODEL OF THE PROPOSED CELL, MODEL THE CELL STRUCTURE, INVESTIGATE CONDITIONS FOR FORMATION OF THE FRONT-AND BACK-SURFACE FIELDS, AND SEARCH FOR A SUITABLEMETHOD OF FORMING LOCALIZED JUNCTIONS IN THE LAYER. AT THE END OF PHASE 1 WE EXPECT TO HAVE DETERMINED THE OPTIMUM STRUCTURE AND UPPER EFFICIENCY LIMIT FOR THIS CELL, PREDICTED CONDITIONS FOR GAAS/ALGAAS INTERFACES WITH LOW INTERFACE RECOMBINATION VELOCITY, AND SELECTED ONE OR MORE METHODS OF JUNCTION FORMATION. WE EXPECT TO BRING THESE TECHNOLOGIES TOGOTHER AND FABRICATE HIGH-EFFICIENCY CELLS IN PHASE II.