We designed, fabricated, and tested for the first time a prototype of nuclear micropower battery with an overall active area about 15 cm 2 consisted in 130 single cells based on Schottky barrier diamond diodes. Diodes selection for the battery assembly was performed on the basis of I-V curves measurements at electron beam irradiation in SEM. A typical energy conversion efficiency of each cell was about 4-6%. To characterize a battery prototype performance, we carried out photovoltaic measurements using different radioisotopes. Under irradiation by 63 Ni source with activity of 5 mCi cm À2 , the output power density of 3 nW cm À2 was obtained. Due to large energy loss of the emitted b particles in source itself, the total battery efficiency was only 0.6%. However, with the longlived 63 Ni isotope, this already gives the battery specific energy of about 120 W Á hr/kg, comparable with the commercial chemical cells. During experiments with high activity 90 Sr-90 Y source, no degradation was observed after 1,400 h of the radiation exposure. The maximum output power density of 2.4 mW cm À2 was achieved using 238 Pu a source. The results display that synthetic diamond is a highly promising material for nuclear microbattery fabrication. A strategy to further cell optimization is also discussed.

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We developed and investigated the vertical diamond Schottky barrier diodes on large area IIb HPHT high quality substrates. The drift CVD layers with boron content of 10 16 and 2 Â 10 17 cm À3 were made. The diodes possess an integral forward current higher than 10 A in the temperature range of 25-200 8C. The self-heating effect further improves the diode forward characteristics. We tested different crystal-to-case thermal interfaces. Diodes have less than 3.5 V forward voltage drop for 10 A at 25 8C and less than 1 V at 200 8C with the onresistance as low as 0.05 Ω (10 mV cm 2 ). We calculated the real Baliga figures of merit (BFOM) of diodes taking into account an incomplete acceptors ionization and a finite substrate resistivity. The low doped diamond conductivity model was used to calculate and optimize the BFOM for various diode designs. The diodes with BFOM up to 200 MW/cm 2 can be made for diamond drift layer with the blocking field of 2 MV/cm and as high as 18000 MW/cm 2 in the case of E MAX $8 MV/cm.