Research And Characteristics Analysis Of Novel Structure Of SiGeC/Si Power Diodes

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.