Mosaic growth of diamond: a study of homoepitaxial flame deposition and etching of {001}-oriented diamond layers

Abstract

This study describes homoepitaxial growth and etch phenomena observed on cubic diamond faces as obtained by the application of an acetylene-oxygen combustion flame. It is demonstrated that flame etching of the diamond substrates prior to growth decreases the number of crystallographic imperfections in the diamond layers especially at the edges. This enables a more uniform distributed step generation by the large number of individual dislocations present in the used natural type IIa diamond substrates. Due to this improvement it appears possible to grow one single crystal diamond layer on top of several closely spaced, well-aligned natural diamond substrates. In the present work the overgrowth of a three-piece mosaic structure with gaps along 〈100〉 as well as along 〈110〉 is reported for the first time. The single crystal nature of this flame-deposited diamond layer could be confirmed by the observation of continuous growth step patterns at the surface across the joint regions. The widths of the gaps between the substrates in the original mosaic structure varied from 7 to 25 μm, which is more than an order of magnitude larger than the gaps along 〈100〉 in two-piece mosaic structures, of which the single crystal overgrowth by HFCVD was previously reported. Comparison of micro-Raman spectra obtained from the joint regions with those from other parts of the overgrown mosaics discussed in the present work, show a larger FWHM of the diamond peak in case of a 〈110〉 joint and a shift of the peak position to higher wave numbers in case of a 〈100〉 joint.