High-voltage Schottky barrier rectifiers and static induction transistors in 4H-SiC

Silicon carbide (SiC) is a promising semiconductor for high-voltage, high-power, and high-frequency devices. This research focuses on the development of process and device technologies for 4H-SiC with special emphasis on high-voltage rectifiers and high-power microwave static induction transistors. Specific contribution of this work include development of new process technologies and their incorporation into high-voltage and high-frequency 4H-SiC devices.; From the process technology standpoint reactive ion etching, ion-implantation and ohmic contacts have experimentally investigated. Effect of gas chemistries, pressure and masking material have been extensively studied to obtain effective residue-free reactive ion etching of SiC with high etch rates. Effective of reactive ion etch induced damage on 4H-SiC planar surfaces as well as trench sidewalls have been studied by XPS analysis and Schottky diodes. Extensive electrical and analytical characterization of ion-implantation of phosphorus in 4H-SiC has been done for the first time. Implanted layers with sheet resistivity as low as 160 Ω/□ have been obtained. It has been shown to be possible to obtain low sheet resistivity (∼260 Ω/□) by annealing the implants at temperature as low as 1200°C. Al/Ni/Al metallization has been utilized to form low-resistivity ohmic contacts to both nitrogen and phosphorus implanted layers in 4H-SiC.; Several high-voltage n-type and p-type high-voltage Schottky rectifiers with either Al, Ni or Ti Schottky metallization have been fabricated. With a particular semiconductor, the choice of whether a Schottky rectifier or a junction rectifier should be used for a particular application depends on the blocking voltage, current density, switching frequency, and operating temperature. A novel technique involving a thin surface implanted layer can be utilized to improve the blocking capability considerably. Schottky rectifiers have been fabricated with near-ideal breakdown voltage of about 925 V with only a 4μm drift region thickness.; Three terminal microwave devices in 4H-SiC such as MEtal Semiconductor Field Effect Transistor (MESFET) and Static Induction Transistor (SIT) have been investigated and compared using 2D device simulations. The SIT is identified as a better choice for lower frequency (∼1 GHz) but high-voltage (≥100V) applications, and the SiC MESFET is shown to be suitable for high-frequency (≥10 GHz) but lower voltage (≥5 100V) applications. Non self-aligned and self-aligned SIT devices have been designed, fabricated and characterized. The non self-aligned devices have pentode-type characteristics with a transconductance of about 7.5 mS/mm. and a drain current of 425 mA/mm. On the other hand, the self-aligned SIT's have triode-like characteristics with a blocking gain of about 1.2. The maximum breakdown voltage of these devices was measured to be about 160 V.