  Semiconductor emitter can possibly achieve sharp cutoff wavelength due to its
intrinsic bandgap absorption and almost zero sub-bandgap emission without
doping. A germanium wafer based selective emitter with front-side
antireflection and backside metal coating is studied here for
thermophotovoltaic (TPV) energy conversion. Optical simulation predicts the
spectral emittance above 0.9 in the wavelengths from 1 to 1.85 um and below 0.2
in the sub-bandgap range with sharp cutoff around the bandgap, indicating
superior spectral selectivity behavior. This is confirmed by excellent
agreement with indirectly measured spectral emittance of the fabricated
Ge-based selective emitter sample. Furthermore, the TPV efficiency by paring
the Ge-based selective emitter with a GaSb cell is theoretically analyzed at
different temperatures. This work will facilitate the development of the
semiconductor-based selective emitters for enhancing TPV performance.
