Theoretical Reseach On Beta Radiation Voltaic Radioisotope Microbattery Based On Wide Bandgap Semiconductor

Nowadays, conventional micropower supply can not meet with the need of the micro-system in many aspects.Beta radiation voltaic radioisotope microbattery（β-RVRIMB）is aideal power supply for microsystem, and it has characters of long life time,small in size,high energy density, working stability,etc. Thus, it is becoming a hot topic in the field ofmicropower supply research. it is the most important thing to improve the energyconversion efficiency for the microbattery.Firstly, This paper introduces the advantages, developmental situation and develop-mental trendency of the RVRIMB. Meanwhile, Its basic structure and working principleare introduced.Secondly, the parameters of RVRIMB are optimized with the MCNPX programm andnumerical calculation method, including the selection of semiconductor materials andradioactive source,optimized design of the electrode and the energy conversion unitparameters （doping method, doping concentration, thickness of the substrate, width of thedepletion region, junction depth, minority carrier lifetime and minority carrier diffusionlength, body resistanse）.The results show that width of optimal depletion region is6mfor the⁶³Ni-GaN β-RVRIMB, the corresponding doping concentration N_A=3×10¹⁹，N_D=9.2×10¹⁵, junction depth and thickness of the substrate are designed to be0.2m and6.2m respectively. Aluminum or aluminum-titanium alloy are the appropriate electrodematerials, and the thickness of palisade electrode should be larger than1m. Then theelectrical model of β-RVRIMB is established, equivalent circuit is analyzed, the theoreticalformulas for short-circuit current, open-circuit voltage, output power, energy conversionefficiency of the microbattery are derived, and some affected factors are analyzed anddiscussed.Finally, β-RVRIMB stacked geometry model and MCNPX simulation model are established. Two methods （Numerical calculation and MCNPX simulation） are used tostudy the self-absorption of source; meanwhile, the relationship among energy depositedpower with the thickness of source layer and GaN energy conversion unit are studied. Theresults show that when the thickness of⁶³Ni source layer and GaN energy conversion unitincrease to3μm,6μm respectively, the energy deposited power becomes saturated, thus, thethickness of the source layer and the GaN energy conversion unit selected to be3μm,6mrespectively are appropriate. The results of simulation of Cuboid and cylindrical micro-battery model show that increasing the contact area of the radioactive source and theenergy conversion unit increases the power output performance of the microbattery.Selection the thickness of GaN energy conversion unit as6.4m, and selection differentthickness of radioactive source to study the power output characteristics of1cm1cmcontact area cuboid stack model though the MCNPX simulation, show that the energyconversion efficiency of the microbattery is affected by self-absorption of source, which isrelated with efficiency of source, energy conversion efficiency of the battery and efficiencyof source decreases with increasing thickness of source. Using the methods of numericalcalculation and MCNPX simulation to study the relationship between efficiency andthickness of source shows that efficiency exponential decrease with the thickness, thesmaller thickness of source, the higher efficiency of source, and the higher energyconversion efficiency of the microbattery, but the smaller short-circuit current and outputpower. Therefore, in practical application, it should according to the specific needs tooptimize and select the thickness of source.