Structural, optical, and electronic properties of nanocrystalline and ultrananocrystalline diamond thin films

The structural, optical, and electronic properties of nanocrystalline diamond thin films grown from a hydrogen-rich CH ₄/H ₂ gas phase via hot filament (HF) CVD and of ultrananocrystalline diamond thin films grown from an argon-rich sp ² gas phase via microwave plasma enhanced (MPE) CVD have been studied. Depending on the growth conditions, these diamond films can have markedly different structural properties, as revealed by atomic force microscopy and Raman spectroscopy. Nevertheless, similarities in the electronic band structure can be seen from transport and optical measurements. In the case of nominally undoped films, both types of material show variable range hopping in localized states near the Fermi level in the whole temperaturerange from 300-650 K. Therefore, the overall density of states has to be the same for these two microstructures. Nitrogen incorporation in the ultrananocrystalline diamond films leads to changes in the optical absorption, which has been investigated using photothermal deflection and spectrally resolved photocurrent spectroscopy.