Enhanced carrier lifetime in bulk-grown 4H-SiC substrates

To devise a means of circumventing the cost of thick SiC epitaxy to generate drift layers in PiN diodes for > 10kV operation, we have endeavored to enhance the minority carrier lifetimes in bulk-grown substrates. In this paper, we discuss the results of a process that has been developed to enhance minority carrier lifetimes to in excess of 30 mu s in bulk-grown 4H-SiC substrates. Measurement of lifetimes was principally conducted using microwave-photoconductive decay (MPCD). Confirmation of the MPCD lifetime result was obtained by electron beam induced current (EBIC) measurements. Additionally, deep level transient spectroscopic analysis of samples subjected to this process suggests that a significant reduction of deep level defects in general and of Z(1)/Z(2), specifically, may account for the significantly enhanced lifetimes. Finally, a study of operational performance in devices employing drift layers fabricated from substrates produced by this process confirmed ambipolar lifetimes in the microsecond range.