Control of surface and bulk crystalline quality in single crystal diamond grown by chemical vapour deposition

TL;DR

This paper presents methods to enhance the crystalline quality of single crystal diamond grown by CVD, focusing on surface damage removal, defect reduction, and birefringence control for advanced technological applications.

Contribution

It introduces ICP etching for surface damage removal, substrate engineering for defect reduction, and demonstrates ultra-low birefringence in high-quality diamond samples.

Findings

ICP etching effectively removes sub-surface damage.

Engineered substrates reduce dislocation density.

Ultra-low birefringence enables improved laser components.

Abstract

In order to improve the performance of existing technologies based on single crystal diamond grown by chemical vapour deposition (CVD), and to open up new technologies in fields such as quantum computing or solid state and semiconductor disc lasers, control over surface and bulk crystalline quality is of great importance. Inductively coupled plasma (ICP) etching using an Ar/Cl gas mixture is demonstrated to remove sub-surface damage of mechanically processed surfaces, whilst maintaining macroscopic planarity and low roughness on a microscopic scale. Dislocations in high quality single crystal CVD diamond are shown to be reduced by using substrates with a combination of low surface damage and low densities of extended defects. Substrates engineered such that only a minority of defects intersect the epitaxial surface are also shown to lead to a reduction in dislocation density. Anisotropy in the birefringence of single crystal CVD diamond due to the preferential direction of dislocation propagation is reported. Ultra low birefringence plates (< 10-5) are now available for intra-cavity heat spreaders in solid state disc lasers, and the application is no longer limited by depolarisation losses. Birefringence of less than 5*10-7 along a direction perpendicular to the CVD growth direction has been demonstrated in exceptionally high quality samples.