SBIR Phase II: Epitaxially Grown GaSb Thin Films on GaAs Substrates For Near-Field Conversion of Heat to Electricity

This Small Business Innovation Research (SBIR) Phase II Project goal is to produce GaSb photovoltaic devices of multicell (MIM) construction for TPV use. Current devices use single cell. MIM devices have significant advantages over single cell in efficiency and cost. A MIM device is composed of many sub-cells physically isolated on the same substrate. This proportionally increases output voltage and decreases output current resulting in lower internal power loss. To date there have been no publications describing MIM Ge or GaSb MIM devices. The Phase I Program demonstrated that high lifetime GaSb can be epitaxially grown on semi insulating GaAs and an IR & D program demonstrated that 50 subcell MIM devices can be fabricated from epitaxial germanium on semi insulating GaAs. Combining these elements will produce an ideal device. Although the Ge MiM is suitable for TPV a GaSb MIM would give a three to tenfold improvement in performance. The broader impact/commercial potential of this project is to economically & efficiently recover waste heat as electricity. 57% of all power generated in the US is rejected as waste heat, however, to date there have been no successful attempts to recover this heat as electricity as opposed to steam for heating purposes. MTPV is developing a thermophotovoltaic solution to address this problem and is a pioneer in the use of near-field evanescent coupling to dramatically increase the power density obtainable from a heat source at a given temperature. MTPV has published a clear demonstration of this phenomenon and is engaged in commercializing its use. Silicon emitter chips designed to transfer energy from a heat source in such a manner as to facilitate the formation of a sub-micron gap are currently being produced in a foundry as well as both single cell and MIM Ge devices. The unique housing that is required to contain these chips and allow insertion into an 1100 degree C furnace is designed/ fabricated at MTPV?s facility where power generation tests are conducted.