A novel Ni/Y 2 O 3 /4H-SiC heteroepitaxial metal–oxide–semiconductor (MOS) betavoltaic cell

A novel vertical heteroepitaxial metal–oxide–semiconductor (MOS) device with extremely high minority carrier diffusion length has been characterized as a betavoltaic cell for power generation in harsh environment applications where solar photovoltaics cannot operate. The MOS structure has been realized by epitaxial growth of 40 nm thick yttrium oxide (Y 2 O 3 ) layer through pulsed laser deposition on 20 μm thick n-type 4H-SiC epilayers with ultralow defect concentration. A 10 nm thick circular (10 mm 2 ) nickel contact was deposited as the gate contact. The surface passivation effect of the Y 2 O 3 layer and its large bandgap resulted in an extremely low leakage current density of 57 pA/cm 2 at a reverse bias of − 250 V which is an order of magnitude less than that observed in benchmark Schottky barrier detectors at the same bias. The thin Y 2 O 3 layer showed minimal absorption of 5486-keV alpha particles when exposed to a 241 Am source and demonstrated a charge collection efficiency of 82%, measured in self-biased mode (0 V applied bias). When exposed to a 5 mCi 63 Ni beta source, the MOS devices demonstrated an output power density of 11 nW/cm 3 and a fill factor > 66% even with a partial illumination. The single pixel MOS devices discussed in this paper have shown a very high prospect to reach the maximum theoretical conversion efficiency of 25% predicted by the Klein relationship.