ion-implanted junctions and conducting layers in SiC

n-type conducting layers have been formed in n- and p-type hexagonal SiC and n-type cubic SiC by implanting ions from column V of the periodic table; N, P, Sb, or Bi. The implantations were made at room temperature and with energies ranging from 5 to 300 keV. The implanted layers have been evaluated by van der Pauw-Hall effect and sheet resistivity measurements and by scanning electron microscopy for anneal temperatures ranging from 1100 to 1800°C. Type conversion of the implanted layers to n-type has been observed after a 750°C anneal. Considerable lattice reordering is suggested from the observed carrier mobility values after annealing at 1600°C.

We have attempted to form p-type layers in n-type SiC by implanting Re, B, Al, Ga, and Tl. Application of anneal procedures identical to those used to form n-type layers have not resulted in measurable p-type layers.

The p-n junctions formed by the donor-implanted layers have been evaluated as a function of anneal temperature. After annealing at 1200°C there is direct evidence of a thick semi-insulating region between the n-layer and the substrate which produces a p-i-n diode characteristic. The thickness of this i-layer can be substantially reduced with additional annealing, resulting in abrupt junction behavior for the diode.

Well-annealed p-n junctions have been characterized as a function of operating temperature over the range of 23 to 400°C. The forward current-voltage behavior of these diodes is dominated by generation and recombination of the carriers in the depletion layer over most of the temperature range. There is some indication of diffusion currents at the highest temperatures. Avalanche breakdown behavior is observed for reverse bias.

The capacitance-voltage behavior of these diodes as a function of frequency and temperature indicate the presence of a deep level which can be explained in terms of the bulk properties of the material.