Fabrication and characterization of ohmic contacts to p- and n-type silicon carbide with applications to p-n junction diodes

This work describes the fabrication and characterization of ohmic contacts to p- and n-type silicon carbide. Silicon carbide is a wide band gap semiconductor that has been recognized for application in high-power and high-temperature microelectronic devices. Because it is still in the maturation stage, there is need for accurate studies of properties of this semiconductor. Among these is the need for characterizing ohmic contacts, since these contacts are the means by which devices are connected to the external world. Emphases have been focused on the 4H- and 6H-SiC polytypes since these polytypes are more readily available and have better electronic qualities. High quality ohmic contacts that have low resistances and excellent high temperature stability is the major aim of ohmic contact research for device applications. To this end, this work has looked at a number of contact metallizations for both p- and n-type SiC.; On p-type SiC, the ohmic contacts fabricated were chromium boride (CrB ₂). tungsten boride (W₂B) and titanium boride (TiB₂ ). Results from these studies indicate that CrB₂ forms ohmic contacts with excellent physical and electrical stability when subjected to high temperatures with very little or no interaction region between the metal layer and the SiC epitaxial layer.; For n-type SiC, niobium (Nb) and nickel silicide (Ni ₂Si) contacts were fabricated on substrates of doping concentration between 3.2 × 1016 cm–3 and 1.0 × 1019 cm–3. Electrical characterization techniques used included the I-V (current-voltage) and TLM (transmission line model) techniques. Physical characterization techniques used were RBS (Rutherford backscattering spectrometry), AFM (atomic force microscopy), TEM (transmission electron microscopy), XPS (X-ray photoelectron spectroscopy) and AES (Auger electron spectroscopy). Results presented also include those from ion implantation studies wherein p-type doping was achieved through Al implantation in order to type-convert n-epilayers. Ohmic contacts were fabricated and characterized on the implanted substrates.; Results are also presented for the fabrication and characterization of p-n junction diodes. The diodes were fabricated using CrB₂ as the p-type metallization. Edge termination techniques using oxide passivation, low energy (keV) and high-energy (MeV) ion implantation were compared. The diodes were analyzed by their breakdown characteristics obtained by pulsed voltage measurements.