Ohmic and rectifying contacts to n-SiC formed by energetic deposition of carbon
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Ohmic and rectifying contacts to n-SiC formed by energetic deposition of carbon Masturina Kracica1, Jim G. Partridge1, Dougal G. McCulloch1, Patrick W. Leech2, Anthony S. Holland2 and Geoff K. Reeves2 1 School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne Vic 3001 2 School of Electrical and Computer Engineering, RMIT University, GPO Box 2476V, Melbourne Vic 3001 ABSTRACT Energetically-deposited carbon contacts to n-type 6H-SiC have exhibited either insulating, rectifying or ohmic electrical characteristics depending on the average energy of the depositing flux and the substrate temperature. Deposition at room temperature and at a low-medium average energy ( 600 ˚C to ensure a low specific contact resistance, ρc. The requirement of high temperature annealing in forming an ohmic metal/SiC contact has been associated with the generation of graphitic carbon as an interfacial layer [13]. Deposited layers of carbon have subsequently been examined as a contact material to SiC. Carbon which was formed by the annealing of SiC [8] and by the pyrolysis of photoresist [9] has been reported to give ohmic electrical characteristics. Other contacts of graphitic carbon have been reported to form rectifying junctions on SiC. The carbon was deposited either as paint with incorporated carbon flakes or as bulk carbon pressed onto the surface [10-12]. The potential therefore exists to form both ohmic and rectifying carbon contacts on n-SiC at relatively low temperatures. Carbon films deposited by energetic filtered cathodic arc on Si have shown interfacial properties which were dependent on the microstructure of the film as determined by the average energy of the carbon flux [14, 15]. Given a sufficient level of deposition energy, an oriented graphitic carbon with high electrical conductivity was deposited in the film [15]. This oriented type of graphitic carbon formed an ohmic contact to both n-Si and p-Si at low temperatures (< 80 ºC) without the requirement for annealing after deposition [15]. In this paper, we have examined for the first time the properties of carbon/ n-SiC contacts deposited by filtered cathodic arc as a function of the deposition energy and temperature of the substrate. The aim of the work has been to form contacts with a range of ohmic to rectifying properties with the applied energy varied through the bias applied to the SiC substrate. Since the deposition process has involved only moderate temperatures, it was possible to pattern the contacts using conventional photolithographic lift-off.
EXPERIMENTAL DETAILS The substrates used in deposition of the carbon films consisted of bulk n-type 6H-SiC (n ~4 x 1017 cm-3). Some films were also deposited on low-resistivity p-Si for examination by transmission electron microscope (TEM). Each substrate was lithographically patterned using AZ1512 photoresist prior to loading into the cathodic arc system. The energetic evaporation was performed using a 99.99% carbon cathode mounted in a Nanofilm Inc. FCVA system (Fig. 1). The system was fitted with a double
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