OPTICAL CHARACTERIZATION OF TEXTURED MICROWAVE CVD DIAMOND

Diamond which exhibits strong preferred orientation in [111], [110] and [100] directions was grown in thicknesses of up to 200 mum by microwave chemical vapour deposition in an Astex reactor. Characterization by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and IR transmission on both free-standing diamond and diamond on silicon substrates was performed. It was found that there is a variation in optical transmission with both the preferred orientation of the diamond and the layer thickness. The lowest CH absorptions were obtained for the [110] material followed by the [100] and then the [111] diamond. The defect-induced single-phonon absorption was highest in the [111] textured material but no significant absorption difference between the [100] and [110] textures was found. By the addition of suitable amounts of oxygen, both the CH-related and the single-phonon absorption could be reduced to undetectable levels. A decrease in CH absorption with layer thickness may be related to the poorer quality and microstructure of the diamond close to the growth interface.