| The SiGeC/Si heterojunction technique is applied to power diodes to improve their reverse recovery characteristics. The lattice structure of strained silicon-based material, the mechanism of compressive and tensile strain, the critical thickness increase of SiGeC material and thermal-stability enhancement of SiGeC related devices are studied in this dissertation. The band structure of SiGeC/Si heteroj unction is analyzed. Based on the proportion betweenΔEC andΔEV inΔEg, it can be concluded that the band structure of SiGeC/Si heteroj unction belongs to'negative-reverse barrier'. The current density expressions of SiGeC/Si diodes are derived under forward bias and their current-transport mechanisms are given.Based on the current transport mechanism of heteroj unction, SiGeC/Si diodes are easy to achieve a low on-state voltage drop under high current density, fast and soft reverse recovery characteristics as well as low reverse leakage current. Compared to lifetime control technology, the contradictions among on-state voltage, reverse leakage current and reverse recovery time are coordinated effectively by SiGeC/Si heteroj unction band-gap engineering. The Ge and C contents of SiGeC alloys are optimized and there is a critical value of C, for a certain Ge content, to achieve the best characteristics in SiGeC/Si diodes. The theory foundation of this critical value is also analyzed.The mobility models and band structure models of SiGeC are obtained by utilizing numeric fitting method. The temperature characteristics between SiGeC/Si and SiGe/Si diodes are analyzed and the enhancement mechanisms of temperature characteristics are studied by the addition of C into SiGe diodes. The results indicate that the thermal stability of SiGeC diodes is improved remarkably due to the addition of carbon into SiGe system. Compared to SiGe diodes, the reverse leakage current of SiGeC diodes is decreased remarkably and its threshold voltage shift is reduced greatly. Furthermore, the fast and soft reverse recovery characteristics are also obtained at 400K for SiGeC diodes.The ideal ohmic contact is applied to SiGeC/Si heterojunction power diodes. The breakdown mechanism of new diodes is studied. The control model of VBR=min(Vpin,Vpnp) is given for the reverse breakdown characteristics of ideal ohmic contact diodes. The expressions of reverse blocking voltage are derived for different breakdown control modes. The conversion condition of two breakdown voltage control modes is given and the relation between breakdown voltage and structure parameters is also presented.A novel structure of ideal ohmic contact SiGeC diodes with base gradual-changing doping is presented. The theory base of reverse breakdown characteristics enhancement is analyzed by the introducing of base gradual-changing doping. The reverse breakdown voltage of p-n-p parasitic transistor in the new diodes is increased substantially, while that of original p-i-n diode is almost not reduced. Therefore, the novel diodes have the merits of high breakdown voltage in a greater range of base doping concentration, which provides more freedom for device design. Besides, because of the inner electrical field of base gradual-changing doping, the reverse recovery time of novel diodes is reduced to some extent without sacrificing their forward characteristics. Based on those, the new diodes can achieve the trade-off among reverse breakdown characteristics and reverse recovery characteristics and forward conducting-state characteristics.Two kinds of SiGeC/Si heterojunction devices with different lateral dimension are fabricated using feasible process flows and implement schemes, and then the sample devices are tested. On the one hand, the consistency between test results and numerical results validates the correctness and of the models presented in this dissertation, which provides a reliable numerical method for the advanced design of SiGeC/Si heteroj unction devices. On the other hand, it provides the process base for the manufacture of SiGeC p-i-n power diodes.
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