【作者】 石彦强；

【导师】 张玉明；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2011， 硕士

【摘要】 碳化硅材料具有禁带宽度大,抗辐照能力强等特点,利用其制备的PiN同位素电池具有输出电压高,抗干扰能力强,受外界温度、压力、电磁场等影响小,可长期稳定工作等优点,有着广泛的应用前景。本文针对基于碳化硅PiN二极管结构的同位素电池进行了研究,主要研究成果如下:一、使用蒙特卡罗软件MCNP模拟单能电子在金属中能量淀积情况,证明了金属对β射线具有很强的阻挡能力,在此基础上设计了5种不同形状的电极;模拟Ni-63β射线在SiC中的能量淀积,结果显示Ni-63β射线在碳化硅中能量的淀积随入射深度的增加而指数递减,因此pn结空间电荷区应尽量靠近表面以达到高的电荷收集效率。根据能量淀积情况设计p+层厚度为0.3μm,i层厚度为3.5μm。二、建立了同位素电池的基本模型,根据模型估计了设计的同位素电池的性能参数,并分析了理想因子、串并联电阻、反向饱和漏电流、放射性活度等对电池性能的影响。模拟结果显示,理想因子越大,输出电压越大;串联电阻较小时影响不明显,但大于时,填充因子会明显下降;并联电阻主要影响填充因子,并联电阻越大,填充因子越大;反向饱和漏电流对开路电压有显著的影响,其值越小,电池的开路电压越大;放射性活度增加,电池的开路电压短路电流都会提高,但电流提高效果更为明显。5×107Ω三、研究了制备同位素电池的主要关键工艺,确定使用CVD法外延形成PiN结构,使用台面结构进行器件隔离,p型欧姆接触使用Ti/Al/Au,厚度分别为50/100/100nm,n型欧姆接触使用Ti/Ni/ Au,厚度分别为50/400/100nm;确定了实验工艺流程,制作光刻版,制作了4H-SiC PiN结同位素电池样品。四、对制作的样品进行了测试,TLM测试结果显示p型欧姆接触性能良好,比接触电阻达到了,处于国内报道的领先水平,接近国际上文献报到的碳化硅p型欧姆接触的最低阻值。从测得的PiN二极管I-V特性曲线中观察开启电压约为3V,提取理想因子约为2.4,反向饱和漏电流密度为10^-13A/cm²。在放射强度10mCi、面积2.5cm²的薄片状Ni-63源的辐照下,该电池的开路电压（Voc）为0.98V,短路电流(I_sc)为0.51nA （12.75nA/cm²）,最大输出功率(P_max)为0.32nW （8.0nW/cm²）,填充因子（FF）为0.64。在放射强度6mCi、面积2.5cm²的薄片状Ni-63源的辐照下,该电池的开路电压(V_oc)为0.95V,短路电流(I_sc)为0.21nA （5.25nA/cm²）,最大输出功率(P_max)为0.14nW （3.5nW/cm²）,填充因子（FF）为0.74。2.567×10 ^-5Ωcm²五、对碳化硅材料其它基于β射线伏特效应的器件进行了初步研究,提出了肖特基同位素电池的改进方案及将碳化硅三极管用于β射线探测器的构想。更多还原

【Abstract】 Silicon carbide （SiC） is a wide bandgap semiconductor with good anti-radiation ability. Due to its wide bandgap, the expected open circuit voltage of SiC PiN junction radioisotope battery is high. The battery also has strong anti-interference ability, hardly affected by the outside temperature, pressure and electromagnetic field. The battery has a prospective future.SiC radioisotope battery with the PiN structure is studied in this paper, main research achievements are as follow:The energy deposition of mono-energetic electrons in metals are simulated with MCNP, proving that metal has a strong stopping power, 5 different electrode patterns are designed based on the conclusion; Energy deposition ofβ-ray emitted from Ni-63 is simulated, the result indicates that the energy deposited in SiC decreases exponentially with penetration depth. In order to achieve high charge collection efficiency, the depletion region should be near the surface. Based on the simulation, the thickness of p+ layer and i layer are designed to be 0.3μm and 3.5μm respectively.Basic model of the micro radioisotope battery is built, and the performance of the designed battery is estimated base on the model. Effect of ideality factor, series resistance, shunt resistance, radioactivity on the battery is analysed, the simulated result indicates that: the greater the ideality factor is, the higher the output voltage is; small series resistance has little effect on the performance, but the fill factor （FF） reduces significantly when the resistance is bigger than 5×10⁷Ω; shunt resistance mainly affect fill factor, the larger the resistance, the bigger the fill factor; leakage current mainly affect open circuit voltage, the smaller the leakage current, the larger the open circuit voltage; increasing radioactivity will improve both open circuit voltage and short current, with the short circuit current improved more significantly.Major key processes during the fabrication of radioisotope battery is studied, we decide to form the PiN structure via Chemical Vapor Deposition （CVD）, use mesa structure to isolate different devices, use 50/100/100nm Ti/Al/Au as p type ohmic contact metals and 50/400/100nm Ti/Ni/Au as n type ohmic contact metals. The fabrication process is designed, photomask is made and the 4H-SiC PiN junction radioisotope battery is fabricated.The sample is tested, TLM test result shows that good p type ohmic contact is formed with the lowest specific contact resistance of only 2, this value is in the domestic leading level, and close to the lowest specific contact resistance of p type SiC. I-V curve obtained shows the turn on voltage is about 3V, ideality factor 2.4 and leakage current 10^-13A/cm²。Under the illumination of 10mCi Ni-63 source that takes up 2.5cm², the open circuit voltage Voc=0.98V, short circuit current I_sc=0.51nA （Jsc =12.75nA/cm² ）, maximum power P_max=0.32nW （power density is 8.0nW/cm²）,and fill factor FF=0.64. Under the illumination of 6mCi Ni-63 source that takes up 2.5cm², the open circuit voltage is Voc=0.95V, the short circuit current I_sc=0.21nA （Jsc =5.25nA/cm²）, maximum power P_max=0.14nW （power density is 3.5nW/cm²）,and fill factor FF=0.74. 2.567×10^-5ΩcmOther kinds of SiC devices based onβ-voltaic effect are studied. Improvement solution of conventional schottkyβ-voltaic battery is provided. SiC transistor used forβray detector is also designed.更多还原