Four-point probe characterization of 4H silicon carbide

Abstract

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 × 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 × 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 Ω 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.