Conduction mechanisms in boron implanted diamond films

The relationship between variable range hopping (VRH) below 300 K and the defects created during 10(13)-10(16) cm(-2) boron ion implantation at 77 K in as-implanted diamond films and films annealed at 800 degrees C is investigated with the help of electron spin resonance (ESR) and optical measurements. The onset D-p=2 X 10(15) cm(-2) of the VRH conduction is attributed to a percolation threshold, and is lower than the amorphization dose D-a=4 x 10(15) cm(-2). From ESR and optical absorption, implantation creates sp(3) carbon dangling bonds (paramagnetic and which act as hopping centres) below D-p and sp(2) bonds (which cause metallic conduction and optical absorption) above D-a. The hopping conduction takes place between localized levels from sp(3) carbon dangling bonds, but only a small proportion of the sp(3) defects participates in this conduction.