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Spectral absorptance of a metal-semiconductor-metal (MSM) thin-multilayer structured thermo-photovoltaic cell was experimentally investigated. A MSM consists of a thin GaSb-semiconductor sandwiched between a top fishnet-type electrode and a flat backside electrode made of gold. A thin GaSb layer was grown on a substrate made of InAs using molecular beam epitaxy, and then all of the InAs substrate was removed using wet etching. The GaSb film was bonded on a surface of gold, which was sputtered on a Si substrate, using a van der Waals bonding method. The top fishnet-type electrode was made using electron beam lithography and a lift-off process. In the case of a 115 nm thick GaSb layer and a square fishnet aperture of a 300 nm × 310 nm size, the spectral absorptance of MSM reached a local peak (95%) at a wavelength of 1.66 µm, which is similar to spectra predicted by numerical simulation. Moreover, the equivalent resonance cavity model and LC circuit model functioned well to indicate the wavelength of several distinct peaks of absorptance.

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A spectral emittance of Metal/Insulator/Metal (MIM) structured emitter was optimized for a spectrally controlled Metal/Semiconductor/Metal (MSM) structured thermophotovoltaic (TPV) cell using a Bayesian optimization method. Corresponding to the spectral absorptance of MSM cell around the bandgap wavelength of GaSb semiconductor, an emittance with an almost unity only around the bandgap could be achieved by selecting the adequate structure of MIM emitter.