单晶硅PN结器件表面钝化对氚辐伏转换性能的影响机理

Radioisotope-voltaic battery is an important branch in radioisotope batteries,in that it is suit for energy supply for ultra-low-power integrated circuit（IC）and ultra-low-power micro electronic and mechanical system (MEMS) sensors on board or even on chip for a very long duration time.For realization of the long duration of the radioisotope-voltaic battery,the radiation-voltaic output and stability of the energy-conversion semiconductor unit is critical. Tritium is the most common isotope in radioisotope-voltaic battery because of its supply convenience and easiness for shield. In our development of tritium beta-voltaic battery, three types of surface passivation were prepared on the same c-silicon PN junction.It was observed that different tritium-voltaic electricity was output by c-silicon PN conversion devices prepared under different surface passivation procedures. Also the stability of the tritium-voltaic electricity output was different with c-silicon PN junction devices under different surface passivation procedures. While there should be no bulk damage in c-silicon PN junction substrate from the tritium sources, taking acount of the energy of the beta electrons and bremsstrahlung X photos. It is meaningful to investigate the changes in surface passivation structures of different passivation procedures before and after radiation from tritium sources. Those changes in surface passivation structures of c-silicon PN junction devices include chemical components and elemental chemical state of Si, P, B, N,O characterized by x-ray photoelectron spectroscopy（XPS） and neutron reflectometry（NR）, dangling bond characterized by electron spin resonance（ESR）, oxide charge density deduced by high-low frequency capacitance-voltage measurement（H-L C-V）, interface trap density deduced by microwave-detected photoconductance decay（ MW PCD） and etc. Through analysis the relationship between these microscopic changes and the intrinsic dark I-V properties, tritium-voltaic electric output, photo response properties of the c-silicon PN junction devices, the radiation damage mechanism of tritium sources on c-silicon PN junction devices and the influence mechanism of surface passivation of c-silicon PN junction devices on tritium-voltaic electrical output and stability can be elucidated. This will provide meaningful support for structure design optimization of radiation-hard c-silicon energy-conversion devices in tritium-voltaic batteries.This will also provide reference for design optimization of beta-voltaic batteries applying other low-energy radioisotopes.

辐伏同位素电池是同位素电池中一个重要分支，氚是辐伏同位素电池中最常用的同位素，单晶硅PN结换能器件在氚源长期辐照下，其辐伏转换电输出及稳定性与PN结器件的表面钝化密切相关。本项目拟制备不同表面钝化层的单晶硅材料、MIS器件及PN结器件，开展氚源原位辐照以及低能电子束、光子束加速辐照实验，通过中子反射谱、电子自旋共振谱、高低频C-V等分析测试，研究不同表面钝化层其界面化学组成与状态、悬挂键、固定电荷密度、界面陷阱密度等微结构随辐照时间的变化。同时，在线测试相应单晶硅器件在氚源及低能离子束作用下的辐伏输出电性能，以及光响应等宏观性能的变化。在微观结构与宏观性能之间建立联系，阐明不同表面钝化层的单晶硅PN结器件在氚源作用下的辐射损伤机理，以及对氚辐伏转换输出与稳定性的影响机理，为氚辐伏同位素电池中抗辐射单晶硅器件的设计提供指导，也为其应用其他低能同位素的辐伏电池的设计提供参考。

针对不同表面钝化材料与结构导致单晶硅器件对氚辐伏转换电性能的初始状态及在氚持续辐照作用下电性能变化趋势有巨大差异的问题，开展了多种表面钝化层对氚辐伏转化性能的影响机理研究。基于国内单晶硅器件生产线常用的三种表面钝化工艺，制备了单一SiO2钝化、SiO2/Si3N4复合钝化、硼硅（磷硅）玻璃/Si3N4复合钝化的单晶硅材料、MIS器件和N+PP+（P+NN+）器件，采用SIMS、刻蚀XPS、NR测试分析了低能电子辐照下不同钝化表面/界面的化学微结构变化，采用少子寿命和C-V特性曲线测试分析了低能电子辐照下不同钝化表面/界面缺陷对材料电学性能的影响，采用400nm~700nm可见光响应和氚源原位辐照辐伏输出测试分析了低能电子辐照下不同钝化缺陷对器件宏观性能的影响，结合分子动力学CASTEP软件模拟计算，分析了不同表面钝化材料与结构的单晶硅PN结器件对氚辐伏转换性能及抗辐照稳定性的影响机理。结果表明单晶硅表面钝化层的结构损伤主要存在于SiO2/Si界面和SiO2的表面，SiO2/Si界面结构损伤并不能通过Si3N4/SiO2复合钝化得到明显改善；辐照对Si3N4表面和Si3N4/SiO2界面影响较小；而采用Si3N4/硼硅（磷硅）玻璃复合钝化有助于增强单晶硅表面及钝化层各界面材料结构的稳定性；磷硅玻璃P掺杂的施主型电子对Si表面电子的排斥作用降低了N型硅的少子（空穴）在Si表面的复合；辐照气氛对器件辐射损伤有显著的影响，尤其对单一SiO2钝化的器件；加速电子束辐照与氚源原位长期辐照结果不尽相同，其原因主要在于辐照气氛控制不同；单一SiO2钝化的N+PP+单晶硅器件在氮气气氛、单一SiO2钝化的N+PP+单晶硅器件和磷硅玻璃/Si3N4复合钝化的P+NN+单晶硅器件在真空气氛中能均保持氚辐伏电池的长期稳定。该工作为设计制备氚辐伏同位素电池用抗辐射单晶硅器件提供了重要的科学依据，为长寿命氚辐伏同位素电池的工程化开发提供了坚实的理论支撑。同时，也对其他β辐伏同位素电池中半导体器件的钝化工艺设计提供参考。