Temperature and Electrical Field Dependence of the Ambipolar Mobility in N-Doped 4H-SiC

In this study, we present results on electrical characterization of bipolar pn-diodes to investigate the temperature and electrical field dependent behavior of ambipolar mobility in n-doped 4H-SiC. Therefore, static current-voltage measurements to calculate the specific differential resistance and dynamical reverse recovery measurements to determine the mean carrier concentration were carried out for different temperatures and forward current densities. The specific differential resistance of the drift layer decreased from 10 mΩcm2 at 80 Acm-2 to 6.6 mΩcm2 at 180 Acm-2, whereas the mean carrier concentration only increased from 4.1015 cm-3 to 8.1015 cm-3, indicating a decreasing ambipolar mobility. The calculated reduction of the ambipolar mobility from 800 cm2V-1s-1 to 650 cm2V-1s-1 in dependence on the current density has to be attributed to an increasing electric field from 150 Vcm-1 to 250 Vcm-1 and increasing carrier scattering due to higher carrier concentrations. For example, at a constant conduction current density of 160 Acm-2, the ambipolar mobility decreases from 710 cm2V-1s-1 at 300 K to 650 cm2V-1s-1 at 450 K.