Al+ implanted 4H-SiC: improved electrical activation and ohmic contacts

The p-type doping of high purity semi-insulating 4H-SiC by Al+ ion implantation and a conventional thermal annealing of 1950 degrees C/5 min has been studied for implanted Al concentration in the range of 1x10(19) - 8x10(20) cm(-3) and 0.36 mu m thickness of the implanted layer. Sheet resistance in the range of 1.6 x 10(4) to 8.9 x 10(2) Omega(square), corresponding to a resistivity in the range of 4.7 x 10(-1) to 2.7 x 10(-2) Omega cm for increasing Al concentration have been obtained. Hall carrier density and mobility data in the temperature range of 140 - 600 K feature the transition from a valence band to an intra-band conduction for increasing Al concentration. In addition, the specific contact resistance of Ti/Al contacts on the 5 x 10(19) cm(-3) Al implanted specimen features a thermionic field effect conduction with a specific contact resistance in the 10(-6) Omega cm(2) decade.