Current transport mechanisms in 4H-SiC pn diodes have been investigated by current-voltage and under-bias-photoemission experiments. In low voltages (1.9 to 2.6 Volts) current recombination dominates forward current. Moreover, carrier recombination takes place on the perimeter of the diodes. From 2.6 to 2.8 Volts a mixed conduction with recombination and diffusion components or recombination through multielectron centers in the space charge region is observed.