Carrier lifetimes in n-type 4H-SiC epilayers were investigated by differential microwave photoconductance decay measurements. Through a correlation study between lifetime and various deep levels, the Z1/2 and/or EH6/7 centers were identified as effective recombination centers. When the Z1/2 (and EH6/7) concentration was higher than 1013/cm3, the inverse carrier lifetime was in proportion to the trap concentration, and the lifetime increased with increasing excitation intensity (density of irradiated photons). Alternatively, other recombination processes limit the lifetime when the Z1/2 concentration was less than 1013/cm3. In this case, the carrier lifetime was decreased by increasing the excitation intensity. Surface recombination and recombination in the substrate were suggested based on numerical analyses as the other recombination paths. By controlling the Z1/2 (and EH6/7) concentration by low-energy electron irradiation, lifetime control was achieved.

Lifetime-Killing Defects in 4H-SiC Epilayers and Lifetime Control by Low-Energy Electron Irradiation. T.Kimoto, K.Danno, J.Suda: Physica Status Solidi B, 2008, 245[7], 1327-36