The carrier lifetime control in p-type 4H-SiC epilayers with intentional aluminum (Al) and boron (B) doping is demonstrated as part of work to develop a p-type “recombination-enhancing layer” for n-channel insulated gate bipolar devices fabricated on p-type substrates. The (Al + B)-doped epilayers (Al: 5 × 1017, B: 4 × 1016 cm−3) showed a very short minority carrier lifetime of less than 20 ns at 293 K, resembling that of highly Al-doped epilayers (Al: 1 × 1019 cm−3). Besides, the minority carrier lifetimes in (Al + B)-doped epilayers are stable against post-annealing in Ar and H2 ambient, while that of Al-doped epilayers varied considerably. PiN diodes with a 10 μm-thick (Al + B)-doped buffer layer inserted on p-type substrates showed no evident degradation after a stress test under a pulse current density of 2000 A/cm2.

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We demonstrate controlled vanadium doping in 4H-SiC epitaxial growth, aimed at reducing the carrier lifetime in the epitaxial layers (epilayers), toward quenching the injection of minority carriers from the drift layer into the substrate in the forward operation of bipolar devices. The doping efficiency of vanadium and the quality of the epilayers were investigated for different gas systems and growth conditions. The photoluminescence spectra and decay curves of band-edge luminescence were evaluated for nitrogen- and vanadium-doped epilayers. The epilayers doped with nitrogen and vanadium demonstrated much shorter minority carrier lifetimes (<20 ns) compared with the epilayer doped with nitrogen only.

Wide-ranging control of carrier lifetimes in n-type epilayers by vanadium (V) doping is attempted toward not only developing a buffer layer to prevent the stacking fault expansion but also improving switching loss in 4H-SiC-based bipolar devices. Control of V doping concentrations in lightly and highly nitrogen (N)-doped epilayers was achieved within the range of 1012–1015 cm−3 by changing the input flow rates of vanadium tetrachloride. Photoluminescence (PL) and deep-level transient spectroscopy analyses revealed that incorporated V atoms create the PL bands within the range of 0.8–1.0 eV, and densities of the deep center at the V3+/4+ acceptor level (Ec − 0.97 eV) increase linearly with V doping concentrations. Accordingly, V doping shortens the minority carrier lifetimes in lightly N-doped epilayers from 3 μs to 40 ns as well as lifetimes in highly N-doped epilayers down to 20 ns at 20 °C, achieving intrawafer carrier lifetime uniformities of 3–10% σ/mean. Furthermore, V doping during epitaxial growth exhibited a nonsignificant memory effect and the V-doped epilayers showed high thermal stability against postprocessing by 1700 °C. We also demonstrated PiN diodes with a 2.4 μm-thick N + V-doped buffer layer (N: 1 × 1018 and V: 1 × 1014 cm−3), showing no degradation after a stress test for 1 h under a direct current density of 600 A/cm2.