Lifetime-killing defects in 4H-SiC epilayers and lifetime control by low-energy electron irradiation

Carrier lifetimes in n-type 4H-SiC epilayers have been investigated by differential microwave photoconductance decay measurements. Through a correlation study between lifetime and various deep levels, the Z(1/2) and/or EH6/7 centers have been identified as effective recombination centers. When the Z(1/2) (and EH6/7) concentration is higher than 10(13) cm(-3), the inverse carrier lifetime is in proportion to the trap concentration, and the lifetime increases with increasing excitation intensity (density of irradiated photons). Alternatively, other recombination processes limit the lifetime when the Z(1/2) concentration is less than 10(13) cm(-3). In this case, the carrier life-time is decreased by increasing the excitation intensity. Surface recombination and recombination in the substrate have been suggested based on numerical analyses as the other recombination paths. By controlling the Z(1/2) (and EH6/7) concentration by low-energy electron irradiation, lifetime control has been achieved. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.