Electrical activation of high concentrations of N+ and P+ ions implanted into 4H-SiC

Comparative Hall effect investigations are conducted on N- and P-implanted as well as on (N+P)-coimplanted 4H-SiC epilayers. Box profiles with three different mean concentrations ranging from 2.5x10 (exp 18) to 3x10 (exp 20) cm-3 to a depth of 0.8 µm are implanted at 500 °C into the (0001)-face of the initially p-type (Al-doped) epilayers. Postimplantation anneals at 1700 °C for 30 min are conducted to electrically activate the implanted N+ and P+ ions. Our systematic Hall effect investigations demonstrate that there is a critical donor concentration of (2-5) X 10 (exp 19) cm-3. Below this value, N- and P-donors result in comparable sheet resistances. The critical concentration represents an upper limit for electrically active N donors, while P donors can be activated at concentrations above 10 (exp 20) cm-3. This high concentration of electrically active P donors is responsible for the observed low sheet resistance of 35 Omega, which is about one order of magnitude lower than the minimum sheet resistance achieved by N implantation.