PHOSPHORUS DOPING OF BORON CARBIDES

Substitution of an electron donor such as phosphorus for a carbon or b oron atom in p-type semiconducting boron carbides is expected to reduc e the hole concentration. Phosphorus-doped boron carbide samples have been prepared by hot isostatic pressing with homogeneous dopant levels of up to one phosphorus atom per ten unit cells. Raman spectroscopy a nd x-ray diffraction confirm the presence of phosphorus within two-ato m intericosahedral chains. The high-temperature dc conductivities of d oped samples were substantially lower than those of undoped boron carb ides. This effect was due to a combination of reduced carrier concentr ations and increased hopping activation energies. The low-temperature ac conductivity of doped samples is also smaller than that of undoped samples. However, the number of carriers participating in the ac condu ction is a very small fraction (< 0.1%) of the total carrier density.