Elimination of carbon vacancies in 4H-SiC employing thermodynamic equilibrium conditions at moderate temperatures

The carbon vacancy (V-C) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the V-C concentration is typically in the range of 10(12) cm(-3), and after device processing at temperatures approaching 2000 degrees C, it can be enhanced by several orders of magnitude. In the present study, both as-grown layers and a high-temperature processed one have been annealed at 1500 degrees C and the V-C concentration is demonstrated to be strongly reduced, exhibiting a value of only a few times 10(11) cm(-3) as determined by deep-level transient spectroscopy measurements. The value is reached already after annealing times on the order of 1 h and is evidenced to reflect thermodynamic equilibrium under C-rich ambient conditions. The physical processes controlling the kinetics for establishment of the V-C equilibrium are estimated to have an activation energy below similar to 3 eV and both indiffusion of carbon interstitials and out-diffusion of V-C's are discussed as candidates. This concept of V-C elimination is flexible and readily integrated in a materials and device processing sequence. (C) 2015 AIP Publishing LLC.