Deep level transient Fourier spectroscopy （DLTFS） measurements are used to characterize the deep impurity levels in n-type 4H-SiC by vanadium ions implantation. Two acceptor levels of vanadium at Ec - 0.81 and Ec - 1.02eV with the electron capture cross section of 7.0 × 10^16 and 6.0 × 10^-16 cm^2 are observed, respectively. Low-temperature photoluminescence measurements in the range of 1.4-3.4eV are also performed on the sample, which reveals the formation of two electron traps at 0.80 and 1. 16eV below the conduction band. These traps indicate that vanadium doping leads to the formation of two deep acceptor levels in 4H-SiC,with the location of 0.8±0.01 and 1. 1 ±0.08eV below the conduction band.
The diffusion behavior of vanadium （V） implanted in SiC is investigated by secondary ion mass spec- trometry. Significant redistribution, especially out-diffusion of vanadium towards the sample surface, is not ob- served after 1650℃ annealing. Higher carrier concentration is obtained due to a lack of compensation of vanadium in the surface region. The electrical characteristics of Ni contacts to V-implanted n-type 4H-SiC are investigated using a linear transmission line method. A specific contact resistance as low as 4.4 × 10^-3Ω · cmA^2 is achieved after annealing at 1050℃ for 10min in gas ambient consisting of 90% N2 and 10% H2 X-ray diffraction analysis shows the formation of Ni2 Si and graphite phase at the interface after annealing. This provides the evidence that the car- bon vacancies,resulting from the out-diffusion of carbon atoms from SiC, contribute to the formation of ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.
