6H-SiC n-type wafers were implanted with Al+ and N+ ions in two steps: first N+ double implantation (65 keV, 5 x 10(16) cm(-2) and 120 keV, 1.3 x 10(17) cm(-2)) followed by Al+ double implantation (100 keV, 5 x 10(16) cm(-2) and 160 keV, 1.3 x 10(17) cm(-2)). The implantation was carried out at a substrate temperature of 800 degreesC, in order to avoid amorphization. In this way, a buried (SiC)(1-x)(AlN)(x) layer could be created. Variable-energy positron Doppler broadening measurements were performed at room temperature using a magnetic transport beam system in order to characterize the vacancy-type defects created by ion implantation. Depth profiles could be evaluated from the measured Doppler broadening profiles. The defect distribution and the defect size after the complete co-implantation are discussed and the contribution of the different implantation steps to the evolution of this defect structure is shown. (C) 2002 Elsevier Science B.V. All rights reserved.