FLAME DEPOSITION AND CHARACTERIZATION OF LARGE TYPE-IIA DIAMOND SINGLE-CRYSTALS

High quality diamond layers 70-400 mum thick have been deposited homoepitaxially on {100} and {110} natural diamond substrates 3-4 mm in diameter by acetylene-oxygen flame deposition. For this purpose, a special substrate-cooling system was used in combination with a burner which had an orifice of 1.6 mm. Microscopic observations revealed that the surface morphology (and thus the mechanism of diamond formation) is strongly dependent on the substrate orientation. Raman spectroscopy showed a significantly lower background fluorescence and a smaller full width at half-maximum (FWHM) of the diamond peak at 1332 cm-1 for layers grown on {100} substrates than for those grown on {100} substrates. Most crystals grown on {100} substrates could be identified as type IIa diamond by IR absorption spectroscopy. However, small traces of nitrogen, not detectable by IR spectroscopy, could be detected by cathodoluminescence as nitrogen-vacancy pairs at lambda = 575 nm. The purest layers mainly exhibit blue band A luminescence. Finally, a large 0.4 carat single-crystal diamond was grown on top of a {110} diamond substrate 6.5 mm x 9 mm. The layer is of type IIa but exhibits cracks parallel to the [112BAR] directions. Most other layers grown on {110} substrates exhibit the same features, but none of the {100} samples showed any sign of crack formation.