Impurity-controlled dopant activation: Hydrogen-determined site selection of boron in silicon carbide

The geometry and formation energy of substitutional B and Al dopants as wel l as their complexes with hydrogen have been calculated in 4H-SiC using fir st-principles methods. Our results show that boron selecting the silicon si te and, therefore, getting activated as a shallow acceptor depends on the p resence of hydrogen which is promoted into the crystal by boron itself. Wit hout hydrogen, boron would mostly be incorporated at the carbon site. Alumi num does not show this behavior: it always selects the silicon site and is incorporated independently of hydrogen. (C) 2001 American Institute of Phys ics.