A huge amount of thermal energy is available close to material surfaces in radiative and nonradiative states, which can be useful for matter characterization or energy harvesting. Even though a full class of novel nano-engineered devices has been predicted over the last two decades for exploiting near-field thermal photons, efficient near-field thermophotovoltaic conversion could not be achieved experimentally until now. Here, we realize a proof of principle by approaching a micron-sized indium antimonide photovoltaic cell at nanometer distances from a hot (~800 K)
Simulations of near-field thermophotovoltaic devices predict promising performance, but experimental observations remain challenging. Having the lowest bandgap among III-V semiconductors, indium antimonide (InSb) is an attractive choice for the photovoltaic cell, provided it is cooled to a low temperature, typically around 77 K. Here, by taking into account fabrication and operating constraints, radiation transfer and low-injection charge transport simulations are made to find the optimum architecture for the photovoltaic cell. Appropriate optical and electrical properties of indium antimonide are used. In particular, impact of the Moss-Burstein effects on the interband absorption coefficient of n-type degenerate layers, and of parasitic sub-bandgap absorption by the free carriers and phonons are accounted for. Micron-sized cells are required to minimize the huge issue of the lateral series resistance losses. The proposed methodology is presumably relevant for making realistic designs of near-field thermophotovoltaic devices based on low-bandgap III-V semiconductors.
In this communication we report on electrical properties of nonintentionally doped (nid) type II InAs/GaSb superlattice grown by molecular beam epitaxy. We present a simple technological process which, thanks to the suppression of substrate, allows direct Hall measurement on superlattice structures grown on conductive GaSb substrate. Two samples were used to characterize the transport: one grown on a semi-insulating GaAs substrate and another grown on n-GaSb substrate where a etch stop layer was inserted to remove the conductive substrate. Mobilities and carrier concentrations have been measured as a function of temperature (77–300 K), and compared with capacitance-voltage characteristic at 80 K of a photodiode comprising a similar nid superlattice.
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