The influence of growth conditions on carrier lifetime in 4H-SiC epilayers

4H-SiC homoepitaxial layers have been grown in a horizontal hot-wall CVD (chemical vapor deposition) reactor and the measured carrier lifetimes have been correlated to the CVD growth conditions. Two different generations of reactors were compared, resulting in measured carrier lifetimes in two different orders of magnitude, from a few hundreds of ns to a few µs. The variations in measured carrier lifetime were correlated to deep level concentrations of the Z1/2 center and the D1 center, seen by photoluminescence. Decreasing the growth temperature clearly prolonged the carrier lifetime and showed lower Z1/2 concentrations, whereas lowering the growth rate only showed a small improvement of the carrier lifetime and no obvious tendency in Z1/2 defect concentrations, indicating that Z1/2 is not the only defect limiting the carrier lifetime. Increasing the C/Si ratio resulted in decreasing Z1/2 concentrations, indicating the carbon vacancy nature of the defect. However, carrier lifetime measurements showed maximum values for a C/Si ratio of 1 but otherwise an increasing tendency for increasing C/Si ratios. The reactor giving higher carrier lifetimes, correspondingly also showed lower Z1/2 concentrations indicating the lifetime limiting property of Z1/2. Furthermore, the D1 defect intensity increased with growth temperature and decreased with increasing C/Si ratio, similar to the Z1/2 concentration.