【作者】 刘静；

【导师】 高勇； 马丽；

【作者基本信息】 西安理工大学 ， 微电子学与固体电子学， 2006， 硕士

【摘要】 传统的Si p-i-n功率二极管由于其材料特性的局限性,很难适应高频化电力电子电路对功率二极管低通态压降、较小的反向漏电流以及快而软的反向恢复特性的要求。SiGe材料因其载流子迁移率高、能带可调等优点受到广泛关注,但是SiGe合金中较大的应变能影响了材料的性能和使用范围。于是出现了SiGeC合金材料,利用C的补偿作用缓解SiGe合金中的应变,增加材料临界厚度,提高器件特性。本文将SiGeC技术应用于功率半导体器件的特性改进,提出了一种p+(SiGeC)-n--n+异质结功率二极管结构。在分析SiGeC合金材料物理特性的基础上,给出了该结构的关键物理参数模型,并在此基础上利用MEDICI模拟、对比分析了C的引入对器件各种电特性的影响。结果表明:在SiGe/Si功率二极管中加入少量的C,在基本不影响器件正向I-V特性和反向恢复特性的前提下,大大减少了器件的反向漏电流; C的加入还减小了器件特性对材料临界厚度的依赖性,提高了器件稳定性。另外,本文还提出了两种快速软恢复SiGeC/Si异质结二极管新结构:理想欧姆接触型和n-区渐变掺杂理想欧姆接触型。模拟结果表明:在第一种新结构中,器件的反向恢复特性大大改善,恢复时间明显缩短,软度因子显著提高,反向峰值电流也有不同程度的降低,但其缺点是,在改善反向恢复特性的同时会使器件的通态特性和反向阻断特性变差;而第二种新结构不仅具有快而软的反向恢复特性,而且n-区中三层渐变掺杂的引入使器件的反向阻断电压增加了将近一倍,正向通态压降也有所降低,很好的实现了功率二极管中Qs-Vf-Ir三者的优化折衷。同时,本文还对合金中Ge/C比例进行了优化设计,认为Ge、C含量分别为20%和0.5%时,器件综合性能最优。更多还原

【Abstract】 The conventional silicon p-i-n diodes are now approaching the theoretical limits and they can not meet the demand of high frequency power electronics circuit for the power diodes with low forward voltage, higher breakdown voltage, low reverse leakage and soft recovery characteristics. Thanks to the bandgap engineering flexibility and higher carrier mobility they provide, SiGe alloys have attracted more and more attention. Indeed, the main obstacle to the commercialization of SiGe devices is the low thermal budget processing that is needed to prevent relaxation of the strained SiGe layers. The introduction of C in SiGe/Si technology may offer new advantages. It has been shown that the tensile strain in SiGe layers can be compensated completely due to the small equilibrium lattice constant of C, which provides a higher critical thickness.A structure of p+(SiGeC)-n--n+ heterojunction power diodes is presented in this paper. Based on the analysis of the physical characteristics of SiGeC alloys, the physical parameter models are given and the effect on the device characteristics by incorporating small-sized carbon atoms substitutionally into SiGe system is simulated and analyzed by MEDICI. The simulation results indicate that the reverse leakage current and the dependence of device characteristics on critical thickness are reduced largely and the stability is improved because of the incorporating carbon atoms into SiGe/Si diodes, on condition that the forward I-V and reverse recovery characteristics are almost unchanged. Besides, two novel kinds of fast and soft recovery SiGeC/Si heterojunction power diodes, the ideal ohmic contact diodes and the ideal ohmic contact diodes with three layers gradual changing doping concentration in n- region, are proposed in this paper. The research results indicate that the reverse recovery characteristics of the ideal ohmic contact diodes are improved largely, the recovery time is remarkably shorted, the soft factor is increased notably and the reverse peak current is also reduced to some extent, while the forward conducting voltage and reverse blocking voltage isdeteriorated; the ideal ohmic contact diodes with three layers gradual changing doping concentration in n- region have faster and softer reverse recovery characteristics and their reverse blocking voltage is doubled and their forward conducting voltage is reduced to some extent, which realizes a good trade-off in Qs-Vf-Ir, compared to ideal ohmic contact diodes. At the same time, the optimal ratio of Ge/C is also presented in this paper and the devices characteristics are optimum for the contents of Ge and C are 20% and 0.5%, respectively.更多还原