Vacancies in He-implanted 4H and 6H SiC epilayers studied by positron annihilation

Defects in epitaxially grown 4H and 6H SiC induced by He-implantation have been studied by positron annihilation and deep level transient spectroscopy. Two major annealing processes of vacancy-type defects appeared at 500-800degreesC and above 1000degreesC irrespective of polytype and conduction type. In n-type samples, the latter process is dominated by two different types of defects. In n-type 6H SiC, Z(1/2) levels emerged after annealing at 800degreesC. The Z(1/2) levels disappeared around 1100degreesC with an appearance of E-1/2 levels. The E-1/2 levels are eventually annealed at 1500-1700degreesC. Similar annealing behavior was observed for the corresponding levels in n-type 4H SiC, i.e., RD1/2 and Z(1/2) levels. The overall annealing behavior of vacancy-type defects by positron annihilation and the deep levels are in good agreement above 800degreesC suggesting that the above deep levels are related to the vacancy-type defects. (C) 2001 Elsevier Science B.V. All rights reserved.