Four-point probe characterization of 4H silicon carbide

We report on four-point probe measurements on SiC wafers as such measurements give erratic data. Current-voltage measurements on n-type SiC wafers doped to 3 x 10(18) cm(-3) are non-linear and single probe I-V measurements are symmetrical for positive and negative voltages. For comparison, similar measurements of p-type Si doped to 5 x 10(14) cm(-3) gave linear I-V, well-defined sheet resistance and the single probe I-V curves were asymmetrical indicating typical Schottky diode behavior. We believe that the reason for the non-linearity in four-point probe measurements on SIC is the high contact resistance. Calculations predict the contact resistance of SiC to be approximately 10(12) Omega which is of the order of the input resistance of the voltmeter in our four-point probe measurements. There was almost no change in two-probe I-V curves when the spacing between the probes was changed from 1 mm to 2 cm, further supporting the idea that the I-V characteristics are dominated by the contact resistance. (C) 2011 Elsevier Ltd. All rights reserved.