14 September 2026. MSE Supplies LLC published an article on September 14, 2026, by Joem Viyar, stating that dislocation density in grown diamond substrates is inherited from the seed plate, not generated by the reactor. The article compares CVD and HPHT growth methods and argues that seed qualification is more important than the choice between them.
The article says threading dislocations in a seed plate propagate vertically into a homoepitaxial CVD layer. Growth does not anneal them out; it extends them layer after layer. Subsurface damage from seed preparation introduces strained lattice regions that nucleate stacking faults and secondary dislocations at the growth interface.
X-ray topography studies of homoepitaxial CVD layers on {001} substrates have traced a specific subset of defects, 45-degree mixed dislocations, to substrate polishing damage. The same work found that dislocation density at the interface can be held below 400 cm⁻² when high-quality type IIa HPHT substrates are used as the seed. Commercial type Ib HPHT diamond runs 10³ to 10⁶ dislocations per cm² depending on size, while higher-grade type IIa material can reach as low as 10³ cm⁻².
For CVD, the article states that sub-nanometer RMS surface roughness is a practical requirement for homoepitaxial seeds, because residual roughness drives non-uniform nucleation and step-bunching. It also notes that off-axis miscut angle affects growth: too shallow a miscut promotes three-dimensional nucleation, and too steep increases defect incorporation. Heteroepitaxial growth on iridium, silicon carbide, or silicon introduces a defect floor from lattice mismatch and thermal expansion differences, independent of seed quality.
The article recommends requesting dislocation density figures (etch pit density or X-ray topography data), a defined miscut angle tolerance, and a stated subsurface damage depth from polishing before a growth run. It states that these are not standard line items on most seed plate quotes.
"The real question isn't CVD versus HPHT—it's whether the seed was qualified before either process began."
Source: MSE Supplies LLC news
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