P-TYPE AND N-TYPE DOPING IN CARBON MODIFICATIONS

We present a density-functional based tight-binding (DF-TB) study of t he possibility of both n- and p-doping of natural and chemical vapor-d eposited diamond, and tetrahedrally bonded amorphous carbon, ta-C. We explain in terms of a charge transfer effect involving partially forme d pi bonds, and carbon defects why neither N, B nor P dope ta-C and wh y N remains fourfold-coordinated in this material but fails to dope. T his failure is suggestive of a novel fully sp(2)-bonded carbon crystal modification in which both shallow n- and p-doping may be possible. ( C) 1998 Elsevier Science B.V. All rights reserved.