Impacts of growth parameters on deep levels in n-type 4H-SiC

Deep levels in $\mathit{n}$ -type $4\text{H-SiC}$ epilayers have been investigated by deep level transient spectroscopy. The ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ centers are dominant in epilayers grown with low $\text{C}/\text{Si}$ ratios during chemical vapor deposition. By increasing the $\text{C}/\text{Si}$ ratio, the ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ concentrations are decreased, while an unknown trap (the ${\text{UT}}_1$ center, $E_c-1.45\text{eV}$ ) is introduced. The ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ concentrations are not changed by increasing the growth rate from 14 to $23\mu \text{m}/\text{h}$ at a fixed $\text{C}/\text{Si}$ ratio. By increasing growth temperature from 1550 to $1750°\text{C}$ , however, the ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ concentrations are significantly increased. From these results, the formation of ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ centers are mainly affected by the $\text{C}/\text{Si}$ ratio and growth temperature rather than the growth rate. These phenomena can be explained with a model that both ${\text{Z}}_{1/2}$ and ${\text{EH}}_{6/7}$ centers are related to a carbon vacancy, which has been recently proposed by the authors.