Reseach On The Theory Of Betavoltaic Nuclear Battery Based On NPN Junction

Since the middle of the20th century, the micro nuclear battery as a kind of idealmicro energy has been paid great attention gradually. Betavoltaic nuclear battery hassome advantages such as long life, small volume and good stability, which makes it asmicro circuits and mems ideal energy source. Therefore, the key point of research ishow to improve the effect of Betavoltaic nuclear battery energy conversion efficiency.In this paper, based on the theory model of voltaic nuclear battery and the energyconversion principle, and studied the63Niradiation source produced byhigh-throughput thermal reactor, we get two main influence factors of Betavoltaicnuclear battery energy conversion efficiency: the efficiency of the source and theconversion efficiency of conversion chip. Optimized the two principle factors,Simulation experimental results show that, the optimization method used in this studycan improve the energy conversion efficiency of Betavoltaic nuclear battery.Mainly work has been done during the study period:(1)63Ni radaition source production: put the high purity nickel into high flux reactorto obtain its isotope (63Ni) after irradiation. Specific activity is about121mCi/g,which can conform to the requirements of Betavoltaic nuclear battery study.(2) conversion chip design: based on the principle of semiconductor materials betavoltaic effect, a new kind of double semiconductor conversion chip has beendesigned. Heavily doped in N area of NPN structure conversion chip and formedgood ohm contact with metal；P area design for P-P+P-structure, slight doped in P-area in order to enlarge the width of depletion region；Heavily doped in P+area inorder to change the conductive performance of semiconductor to induce theresistance of conversion chip.(3) MCNP4C numerical simulation calculation: we use MCNP4C program tosimulate and analyse the beta particles transport in semiconductor, we obtained the matching parameter of doping behavior, doping concentration, and basic layerthickness, depletion layer width, junction depth, minority carriers lifetime andminority carriers diffusion length. Simulation results show that, the best width ofsilicon NPN junction Betavoltaic nuclear battery depletion region is2μm, dopedconcentration is ND=2×1020cm-3， ND=3×1016cm-3; Junction depth and P-areathickness are designed as0.2μm and20μm; The model and simulation are basedon conversion chip parameters. According to the simulation results, the shortcircuit current, open circuit voltage and the ideal conversion efficiency of betaradiation betavoltaic nuclear battery could be calculated as594nA,0.233V and0.261%respectively.(4) Verification of Simulation Results: we produced the doublesemiconductor conversion chip, use electron beam to simulate beta particles andirradiate conversion chips. The parameter of conversion chip has been shown asfollows: the diameter of junction area is6cm, use the300um P-<111>monocrystalsilicon as basement, the doping concentration(NA) is1.87×1016cm-3, the Specificresistance is0.8·cm, the doping concentration in N area is1.2×1021cm-3,Diffused junction depth is2μm, square Specific resistance is0.6·cm. Theconversion efficiency could be calculated as0.241%.,This study can provide theoretical guidance for high efficient betavoltaic nuclearbattery research and manufacture.