Effects of Implantation Temperature on Sheet and Contact Resistance of Heavily Al Implanted 4H-SiC

Effects of implantation temperature on electrical properties of heavily-Al-doped 4H-SiC layer formed with Al implantation have been investigated. To form the p(++) with the original 4H-stacking structure, the implantation temperature above 175 degrees C is needed. A decrease in the implantation temperature below 250 degrees C leads to an increase in the N(A)-N(D). It is suggested that an increase in the density of vacancies with a decrease in the implantation temperature promotes the Al substitution to lattice sites during activation annealing. The lower-temperature implantation also causes a decrease in activation energy for the p-type electrical conduction and a decrease in p-type ohmic contact resistivity. We presume that the increase in the Al acceptors at low-implantation temperatures gives expansion of the impurity bands and formation of valence band tail-states, causing the decrease in the impurity binding energy. The properties obtained with the lower-temperature implantation are desirable for practical applications especially at low temperatures.