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

High quality diamond layers 70-400 mum thick have been deposited homoe pitaxially on {100} and {110} natural diamond substrates 3-4 mm in dia meter by acetylene-oxygen flame deposition. For this purpose, a specia l 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 st rongly dependent on the substrate orientation. Raman spectroscopy show ed a significantly lower background fluorescence and a smaller full wi dth 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. M ost crystals grown on {100} substrates could be identified as type IIa diamond by IR absorption spectroscopy. However, small traces of nitro gen, not detectable by IR spectroscopy, could be detected by cathodolu minescence as nitrogen-vacancy pairs at lambda = 575 nm. The purest la yers mainly exhibit blue band A luminescence. Finally, a large 0.4 car at single-crystal diamond was grown on top of a {110} diamond substrat e 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} substrat es exhibit the same features, but none of the {100} samples showed any sign of crack formation.