# Large Platform Growth Effect of Single-Crystal Diamond on the Regulation of Its Dielectric Properties and Stress for THz Applications

## TL;DR

This paper shows how a new growth method for single-crystal diamond improves its surface quality and dielectric properties for terahertz applications.

## Contribution

A novel 'two-step method' is introduced to achieve large platform growth in single-crystal diamond, reducing stress and enhancing dielectric performance.

## Key findings

- The RMS roughness of diamond surfaces decreased from 5 nm to 0.4–1.0 nm using the platform growth method.
- Stress from step growth was reduced to 0.1976 GPa, and dielectric properties improved at THz frequencies.
- Large platform growth minimizes dislocation pile-up, enabling ultra-precision machining of diamond windows.

## Abstract

The single-crystal diamond (SCD) possessing both favorable dielectric properties and low stress is esteemed as the ideal material for terahertz windows. The intrinsic step-like growth pattern of SCD can easily lead to stress concentration and a decrease in dielectric performance. In this study, a “two-step method” was designed to optimize the growth mode of SCD. A novel large platform growth pattern has been achieved by controlling diamond seed crystal etching and the epitaxial layer growth process. The experimental results indicate that, compared with the traditional step-like growth model, the root mean square (RMS) roughness of as-prepared SCD reduced from 5 nanometers (step growth) to 0.4~1.0 nanometers (platform growth) within a 5 μm × 5 μm area. Furthermore, the growth step height difference diminished from 30 nm to 3~4 nm, thereby mitigating stress induced by steps to a mere 0.1976 GPa. Additionally, at frequencies ranging from 0.1 to 3 THz, the diamond windows exhibit lower refractive index, dielectric constant, and dielectric loss. Finally, large platform growth effectively reduces phenomena such as dislocation pile-up brought about by step growth, achieving low-damage ultra-precision machining of diamond windows measuring 1 mm in diameter.