Schottky and ohmic contacts to silicon carbide with device applications

Fabrication and electrical characterization of Schottky and ohmic contacts to silicon carbide (SiC) are examined in this work. Silicon carbide exhibits improved performance over silicon in high power, high frequency, high temperature, and radiation intensive applications. Unlike silicon, however, the quality of commercially available SiC has improved dramatically in the last decade. Therefore, initial analysis identifies a wide range of electrical behavior in Schottky diodes. The Schottky barrier height was measured using four distinct techniques: the standard thermionic emission I-V method the Norde plot method, the activation energy method, and from the temperature dependence of reverse characteristics. Thermionic emission theory predicts reverse leakage currents that are incommensurate with measured values at room temperature, but in closer agreement at higher temperatures. The technique of plotting the ideality factor as a function of forward voltage (ideality profiling) is used to identify possible current mechanisms responsible for the range of behavior in the electrical characteristics. Non-ideal behavior could be identified in the ideality proNe by the presence of peaks, which became dimini hed at increasing temperatures, indicating that non-thermionic conduction dominates reverse leakage currents at room temperature. These peaks were also observed ta diminish by Ar implantation of material surrounding the contacts. This method of implantation is also employed in a study of the thermal stability of the Ni-SiC contact. Reverse leakage current, Schottky barrier height and physical stability were examined for long-term anneals at {dollar}rm 300spcirc C.{dollar} Electrical behavior of ideal contacts and physical analysis demonstrate good stability for 9000 hours of thermal stressing. Argon implantation appears to improve the reliability of this contact.; Ohmic contacts on n-type SiC were produced using nickel silicide, with both Ni and nichrome as starting materials. Test structures were fabricated on a range of dopant concentrations {dollar}rm (3.2times 10sp{lcub}16{rcub} cmsp{lcub}-3{rcub}{dollar} to {dollar}rm 1.3times 10sp{lcub}19{rcub} cmsp{lcub}-3{rcub}){dollar} and the results of electrical measurements compared. The specific contact resistivity was measured for the range of n-type dopant concentration using the linear, one dimensional transmission line method, and compared with theoretical predictions. These results indicate that microscopic properties of the SiC-contact interface are important to the nickel silicide contact. The nichrome contact exhibited similar electrical behavior to the nickel contact, but performed much more satisfactorily with respect to wirebonding and as a diffusion barrier layer to Au capping layers which are necessary for wirebonding. Physical characterization of the nichrome contact was also carried out in the form of Rutherford backscattering analysis and Auger depth profiling, and reasons for improved performance of the nichrome contact are discussed.; Silicon carbide metal-semiconductor field effect transistors were fabricated using the ohmic and Schottky contacts developed in this study and were characterized from {dollar}rm 25spcirc C{dollar} to {dollar}rm 400spcirc C.{dollar} Limitations of device operation based on gate contact performance were examined by fabricating devices with both Mo and Ni gate metallizations. The extrapolated threshold voltage, channel conductance, transconductance, output resistance, and small-signal voltage gain were measured as a function of temperature for 6H and 4H-SiC devices. These results indicate that device performance in small-signal analog applications is adequate up to {dollar}rm 300spcirc C{dollar} using Ni Schottky gate metallization. Limitations on theoretical accuracy imposed by contact-related parameters such as parasitic resistance effects are also discussed.