Flame deposition and characterization of large type IIA diamond single crystals

Abstract

High quality diamond layers 70-400 gm 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 { 110} 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 2 = 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 ram.The layer is of type IIa but exhibits cracks parallel to the directions.Most other layers grown on { 110} substrates exhibit the same features, but none of the { 100} samples showed any sign of crack formation.