Synthesis Of Large Homoepitaxial Single Crystal Diamond By DC Arc Plasma Jet CVD With Rotating Arc And Operated At Gas Recycling Mode

In the present investigation, the effects of the growth parameters (such as substrate temperature, CH4/H2ratio, substrate quality, substrate pretreatment, nitrogen addition, etc.) on the surface morphology, the growth rate and the quality of the synthesized single crystal diamond by high power DC Arc Plasma Jet with arc rotating and operated at gas recycling mode have been studied using optical microscopy, and Raman spectroscopy. The growth rate up to17.4μm/h has been obtained in the single crystal diamond sample deposited at1000℃with CH4/H2=0.813%(in volume fraction), exhibiting relatively smooth surface morphology with the typical feature of the step-flow growth, and no non-epitaxial diamond crystallites. Under the optimum synthesis conditions, large size (7.5mm×7.5mm) polished freestanding single crystal diamond plate up to1.03mm thickness has been successfully produced for the first time by DC Arc Plasma Jet with rotating arc and operated at gas recycling mode, and characterized by UV-Vis-IR absorption, photoluminescence and Raman spectroscopy, as well as high-resolution X-ray diffraction. The (400) peak of the CVD diamond is very sharp with a FWHM of0.013°only and7.6ppm incorporated nitrogen, indicating a rather good crystallinity. Besides the NV related defects, the presence of H3and H2centers as well as the513nm line indicated the existing of the aggregated nitrogen in the CVD single crystal diamond without heat treatment. To our knowledge, it may be the first report on the finding of the aggregated nitrogen in the as-grown CVD synthetic single crystal diamond.Based on the observations on the growth mode and the characterization of the nature of the interface between the epitaxial layer and the HPHT substrate, it showed that the first step of the epitaxial diamond growth might start from the preferential two dimensional nucleation and grow at the preexisting high density etch pits produced by the in situ H/Ar plasma pretreatment, and gradually change to a step-flow growth as the time running. That led to an interface transition layer about15μm thickness between the epitaxial diamond and the type Ib HPHT substrate, exhibiting a strong stress and fluorescence. Smooth surface growth was promoted by adopting a mixed growth mode of the off (100) axis growth and the3D mode growth, which means that it is possible to avoid the non-epitaxial diamond nucleation surrounding the HPHT seeds and ultimately achieve a single crystal CVD diamond larger than its HPHT seed. The synthesized single crystal diamonds were used to produce radiation detectors with MSM structure. The Ⅰ-Ⅴ characteristics of the detector showed that the full charge depletion electric field of the single crystal diamond was approximately1V/μm and the dark current was only0.56nA. and the electrical breakdown did not happen at2500V.