Wide-ranging control of carrier lifetimes in n-type 4H-SiC epilayer by intentional vanadium doping

摘要

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 10(12)-10(15)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 0.8-1.0eV, and densities of the deep center at the V3+/4+ acceptor level (E-c-0.97eV) increase linearly with V doping concentrations. Accordingly, V doping shortens the minority carrier lifetimes in lightly N-doped epilayers from 3 mu s to 40ns as well as lifetimes in highly N-doped epilayers down to 20ns at 20 degrees C, achieving intrawafer carrier lifetime uniformities of 3-10% sigma/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 degrees C. We also demonstrated PiN diodes with a 2.4 mu m-thick N+V-doped buffer layer (N: 1x10(18) and V: 1x10(14)cm(-3)), showing no degradation after a stress test for 1h under a direct current density of 600A/cm(2).