Influence of Net Doping Concentration on Carrier Lifetime in 4H-SiC Substrates

Lightly nitrogen-doped (N-doped) and vanadium-doped (V-doped) 4H-SiC single crystals grown by physical vapor transport were used to investigate the effect of net doping concentration on carrier lifetime. The carrier lifetime in N-doped and V-doped 4H-SiC substrates was measured using microwave photoconductance decay. The resistivity mapping of the 4H-SiC wafers was measured using a contactless eddy current to reveal the relationship between resistivity and net doping concentration. Raman spectroscopy and secondary ion mass spectroscopy were recorded to determine the carrier concentration and impurity distribution. The results show that the net N doping concentration, expressed by N_D − N_A (donor nitrogen compensated by acceptor boron and aluminum), was responsible for carrier lifetime in N-doped 4H-SiC substrate. For V-doped 4H-SiC substrates, the experimental details clearly demonstrated that the carrier time was affected not only by V concentration (N_V), but also by the shallow level impurity concentration. When N_D − N_A > N_V, the net V₁ doping concentration expressed by (N_D – N_A) − N_V determined the carrier lifetime. The net V₂ doping concentration expressed by N_V − (N_D − N_A) determined the carrier lifetime when N_V > N_D − N_A, and the carrier lifetime decreased with increasing net V₂ impurity concentration. The maximum carrier lifetime was obtained when N_D − N_A ≈ N_V.