Effects of annealing on carrier lifetime in 4H-SiC

Abstract

We present results of a thermal anneal process that increases the minority carrier lifetime in SiC substrates to in excess of 3μs, compared to the starting as-grown substrates with lifetimes typically in the <10ns range. Measurement of lifetimes was conducted using microwave-photoconductive decay. Electron beam induced current measurements exhibited minority carrier diffusion lengths of up to 65μm, confirming the enhanced carrier lifetime of the annealed substrate material. Additionally, positron annihilation spectroscopy and deep level transient spectroscopic (DLTS) analysis of samples subjected to this anneal process indicated that a significant reduction of deep level defects, particularly Z1∕Z2, may account for the significantly enhanced lifetimes. The enhanced lifetime is coincident with a transformation of the original as-grown crystal into a strained or disordered lattice configuration as a result of the high temperature anneal process. The operational performance of p-i-n diodes employing drift layers fabricated from the annealed high-lifetime substrates confirmed conductivity modulation in the diodes consistent with ambipolar carrier lifetimes in the microsecond range.