P-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by pulsed laser deposition and their application to photodetectors

p-Type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were fabricated by pulsed laser deposition with boron-blended graphite targets. The X-ray diffraction patterns exhibited diffraction peaks attributable to diamond-111 and diamond-200. Electrical conductivity clearly increased with boron content. The near-edge X-ray absorption fine structure revealed that doped boron atoms partially replace hydrogen atoms that terminate the dangling bonds of UNCD grains. Heterojunction diodes comprising p-type UNCD/a-C:H and ntype Si showed a strong photoresponse that originates from UNCD grains in the wavelength range between 200 and 280 nm. We experimentally proved that boron-doped UNCD/a-C:H is a new promising p-type semiconductor for photodetection.