Investigation of nickel-63 radioisotope-powered GaN betavoltaic nuclear battery

This work describes the theoretical and experimental investigation of an in-house produced ⁶³Ni radioisotope-powered GaN-based direct conversion (betavoltaic) nuclear battery. GaN p-n junction device with 1-mm² area was fabricated and irradiated by the ⁶³Ni plate source. Short-circuit current and open-circuit voltage of the battery were measured, and current-voltage curves were plotted. The energy stored in battery, maximum power, and efficiency parameters were calculated. Monte Carlo modelling was used to investigate radioisotope's self-absorption effect, the optimization of semiconductor and source thickness, transport, and penetration of beta particles in semiconductor junction. A large fraction of beta particle energy emitted from ⁶³Ni source is absorbed within 1 μm of the semiconductor junction on the basis of the simulation results. Epitaxial growth of GaN was performed using metal-organic chemical vapour deposition (MOCVD) system. Monte Carlo simulation with MCNPX was used to determine optimum ⁶³Ni radioactive film thickness. ⁶³Ni film was electroplated on one face of 1-mm² copper plate and mounted 1 mm over the semiconductor device. A ⁶³Ni source with an apparent activity of 0.31 mCi produced 0.1 ± 0.001 nA short-circuit current (I_sc), 0.65 V ± 0.0022 open-circuit voltage (V_oc), and 0.016 nW ± 0.0002 maximum power (P_max) in the semiconductor device. The filling factor (FF) of the betavoltaic cell was 25%, and the conversion efficiency (ɳ) was 0.05%. Finally, experimental results were compared with theoretical calculations.