INDIUM GALLIUM ARSENIDE THERMOPHOTOVOLTAIC ENERGY CONVERTERS

THERMOPHOTOVOLTAIC INDIUM GALLIUM ARSENIDE (INGAAS) CELLS ARE PROPOSED FOR CONVERGING ENERGY FROM A RADIOISOTOPE POWER SOURCE, THE GENERAL PURPOSE HEAT SOURCE (GPHS), INTO ELECTRICITY WITHCONVERSION EFFICIENCIES CONSIDERABLY HIGHER THAN THOSE OBTAINED WITH THERMOELECTRIC GENERATION. IN GAAS IS A TERNARY SEMICONDUCTOR ALLOY WHOSE BANDGAP CAN BE VARIED FROM 0.36 EV TO 1.42 EV. THE 0.74EV IN0.53GA0.47 AS COMPOSITION IS PARTICULARY USEFUL SINCE HIGH QUALITY IN GAAS CAN BE GROWN LATTICE-MATCHED TO INDIUM PHOSPHIDE (INP) WAFERS,RESULTING IN GOOD P-N JUNCTIONS AND HIGH CONVERTER EFFICIENCY. THIS 0.74 EV BANDGAP IS TO HIGH FOR EFFICIENT THERMOPHOTOVOLTAIC CONVERSION WITH THE 1100 DEGREE CENTIGRADE GPHS. A BANDGAP OF 0.5 EV WOULD DELIVER TWICE THE POWER IF IT WERE NOT FOR DEFECTS CREATED WHEN INGAAS IS GROWN MISMATCHED. ANOPTIMIZATIO STUDY OF THIS TRADEOFF BETWEEN CELL DEGRADATION DUE TO MISMATCH AND THE INCREASED OUTPUT POWER POSSIBLE BY MATCHING THE CELL BANDGAP TO THE GPHS RADIATION SPECTRUM IS PLANNED INTHIS PROJECT. PHASE I WILL GROW INGAAS WITH BANDGAPS OF 0.74, 0.70, 0.65, 0.55, AND 0.50 EV, FABRICATE CELLS, AND TEST THEM TO DETERMINE THE RELATIVE DEGRADATION OF THE CELLS AS THE INGAASCOMPOSITION IS MOVED AWAY FROM AN EXACT LATTICE-MATCH TO INP. IN PHASE II, THE PHASE I CELL THAT DELIVERED THE HIGHEST OUTPUT POWER UNDER THE GPHS RADIATION WILL BE EXPERIMENTALLY DEVELOPED INTO A PROTOTYPE POWER CONVERTER. IN PHASE III, A CONVERTER WILL BE DEVELOPED FOR A SPECIFIC MISSION.