Passivation of Surface Recombination at the Si-Face of 4H-SiC by Acidic Solutions

We carried out carrier lifetime measurements for 4H-SiC single crystals in aqueous solutions with various pH by the microwave photoconductivity decay method. For both n- and p-type 4H-SiC, carrier lifetimes measured by Si-face excitation were longer in acidic aqueous solutions compared with carrier lifetimes measured in other solutions. On the other hand, for C-face excitation, carrier lifetimes did not depend on immersion solutions. These results indicate that carrier recombination centers at the surface of the Si-face was passivated by hydrogen ions. We also estimated surface recombination velocities Ss by a numerical analysis. S of the Si-face was reduced from 700 cm/s (in Na2SO4 1 M) to 200 cm/s (in H2SO4 1 M) for the n-type 4H-SiC.