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With its excellent properties such as high thermal conductivity, strong radiation resistance and high electron mobility, diamond has become one of the most suitable materials for radiation detectors. Detector-grade diamond requires low impurity content, low dislocation density and other defects. However, it is very difficult to keep low impurities and low dislocations simultaneously in the actual crystal growth process. In this study, microwave plasma chemical vapor deposition (MPCVD) method was used to grow diamond layer on two high-quality HPHT diamond substrates with the previously optimized process conditions. The nitrogen impurity content and structure of the HPHT substrate and growth layer were characterized and analyzed. The results show that, the content of nitrogen impurity on two HPHT substrates are 7. 1 x 10-6% and 4. 04 x 10-8%, respectively, whereas in their epitaxial diamond layers, the nitrogen impurity content are 2. 1 x 10-7% and 5 x 10-8%, respectively. The full width at half-maximum of the rocking curve shows that the dislocation density of the MPCVD growth layer is comparable to the HPHT substrate, though some dislocations were introduced into the MPCVD growth layer, which increases the stress. Overall, the dislocations in the HPHT substrate and epitaxial layer of single crystal diamond are in the same order of magnitude. The high-purity single crystal diamond prepared in this work may be used in nuclear radiation detection and semiconductor fields. [ABSTRACT FROM AUTHOR]

In the present investigation, a nitrogen-doped multilayer homoepitaxial single crystal diamond is synthesized on a high-pressure high temperature (HPHT) Ib-type diamond substrate using the microwave plasma chemical vapor deposition (MPCVD) method. When 0.15 sccm of nitrogen was added in the gas phase, the growth rate of the doped layer was about 1.7 times that of the buffer layer, and large conical and pyramidal features are formed on the surface of the sample. Raman mapping and photoluminescence imaging of the polished cross sectional slice shows a broadband emission, with a characteristic zero phonon line (ZPL) at 575 nm in the doped layers, and large compressive stress was formed in the nitrogen-doped layers. X-ray topography shows that the defects at the interface can induce dislocation. The pyramid feature is formed at the defect, and more nitrogen-related defects are formed in the pyramid region. Thin nitrogen-doped multilayers were successfully prepared, and the thickness of the nitrogen-doped and buffer layers was about 650 nm each. The indentation measurements reveal that the thin nitrogen-doped multilayers are ultra-tough (at least ~22 MPa m1/2), compared to the Ib-type HPHT seed substrate (~8 MPa m1/2) and the unintentionally doped chemical vapor deposition (CVD) single crystal diamond (~14 MPa m1/2). [ABSTRACT FROM AUTHOR]

Microwave plasma chemical vapor deposition (MPCVD) was used to grow single-crystal diamonds on two types of single-crystal diamond seed substrates prepared by high-pressure, high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The quality of diamonds grown on the different seed substrates was compared. Fluorescence characteristics showed that the sectors of the HPHT seed substrates were obviously partitioned. Raman and absorption spectra showed that the CVD seed substrate produced higher-quality crystals with fewer nitrogen impurities. X-ray topography showed that the HPHT seed substrate had obvious growth sector boundaries, inclusions, dislocations, and stacking faults. The polarization characteristics of HPHT seed substrate were obvious, and the stress distribution was not uniform. When etching HPHT and CVD seed substrates using the same parameters, the etching morphology and extent of different growth sectors of the two substrates differed. Although extended defects were inevitably formed at the interface and propagated in the CVD layer, the dislocation density of a 1 mm-thick CVD layer grown on a CVD seed substrate was only half that of a 1 mm-thick CVD layer grown on an HPHT seed substrate. Therefore, the use of CVD seed substrate enabled the growth of a relatively higher-quality CVD single-crystal diamond. [ABSTRACT FROM AUTHOR]

Surface etching of single-crystal diamond (SCD) in hydrogen plasma plays a decisive role for high-quality homoepitaxy and surface conduction of diamond. The complexity of surface/subsurface condition such as defects would give rise to the distinct morphology features and even further result in the unpredictable properties. Correspondingly, the evolutionary relationship between the morphology and electrical properties of mechanically polished SCDs which have typical cleavage damage in microns depth after hydrogen plasma treatment still needs to be further completed. In this work, the chemical vapor deposited (CVD) SCDs with uniform polishing-caused subsurface cleavage were immersed in microwave hydrogen plasma for variable duration. Time-dependent morphological evolution, multi-mode etched pits (EPs) (resulting from local defects/cracks and dislocations) and associated etching mechanism were comprehensively studied. At the early stage of plasma treatment before 60 min, owing to the obvious surface roughing generated by preferential etching (with the rate of >400 nm/h) of severe mechanically damaged regions, the hole mobility was significantly deteriorated, also accompanying with the apparent drop of sheet concentration. Concurrently, the deposited surface sp 2 amorphous carbon (a -C) nanodots on diamond surface and non- sp 3 hydrogen bonds reconstruction, which arising from defect-etching produced local abundant carbon-containing radicals or possible exfoliation generated by hydrogen penetration of massive defective regions, also would play an adverse role for the conduction associated with (100) C–H surface. However, the surface roughness was reduced from the maximum 13.2 nm–4.2 nm by prolonging etching, resulting from the smoothing effect of small-angle crystal misorientation on waved height difference related to the uniform (111) cleavage and the removal of dense irregular EPs associated with polishing-induced local defects as well as the vanishing of surface a -C nanodots. In this case, the improvement of surface electrical properties together with the negative correlation of the mobility and sheet concentration were appeared by the gradual formation of (100) diamond surface and the building of uniform (100) C–H bonds. • CVD SCDs with typical subsurface damages(defects) were treated in pure hydrogen plasma. • Morphology evolution associated with polishing defects was time-dependently presented. • Surface sp2 nanodots deposition from defect-etching and CH reconstruction would affect electrical properties. [ABSTRACT FROM AUTHOR]