ON THE ELECTRONIC-PROPERTIES OF BETA-RHOMBOHEDRAL BORON INTERSTITIALLY DOPED WITH 3D TRANSITION-METAL ATOMS

The controlled modification of the p-type character of pure boron-rich solids to n-type by suitable doping is an essential prerequisite for technical applications. Interstitial doping of beta-rhombohedral baron with V, Cr, Fe and Ni fulfils this requirement, while Cu and Co do no t. Comparative investigations of the Seebeck coefficient, the DC elect rical conductivity, the optical absorption and the dynamical conductiv ity of B-V, B-Co and B-Fe lead to the conclusion that donor levels pos itioned between the conduction band and the uppermost intrinsic electr on trapping level and of sufficient density to overcompensate unoccupi ed valence and gap states are necessary for n-type conductivity. In co ntrast to Fe, the interstitial accommodation of V atoms seems to reduc e the concentration of possible gap states. (C) 1997 Elsevier Science S.A.