Templated growth of diamond optical resonators via plasma-enhanced chemical vapor deposition

At a Glance

Metadata	Details
Publication Date	2016-08-22
Journal	Applied Physics Letters
Authors	Xue Zhang, Evelyn L. Hu
Institutions	Harvard University
Citations	8
Analysis	Full AI Review Included

Technical Documentation and Collateral: MPCVD Diamond Optical Resonators

# Executive Summary

This research demonstrates a powerful bottom-up approach for creating high-quality, pyramid-shaped diamond optical resonators using Microwave Plasma-Enhanced Chemical Vapor Deposition (MPCVD) through patterned silica masks. This technique is highly relevant for integrating quantum emitters (NV/SiV centers) into photonic circuits.

Novel Fabrication: Utilizes templated epitaxial growth via MPCVD, eliminating destructive top-down etching of diamond, thus preserving the pristine host lattice environment for color centers.
High Photonic Performance: Achieved Quality Factors (Q) up to 600 and demonstrated low Mode Volumes (V) as small as 2.5(λ/n)³, maximizing the Purcell enhancement factor (Q/V).
Material Quality Confirmation: Raman spectroscopy confirmed the high material quality of the grown diamond resonators, reporting a FWHM of 2.60 ± 0.11 cm^-1, comparable to the HPHT substrate.
In Situ Emitter Integration: Successfully incorporated Silicon-Vacancy (SiV) and Nitrogen-Vacancy (NV) color centers directly during the growth phase, essential for integrated quantum applications.
Deterministic Resonances: Demonstrated control over resonant wavelengths by systematically varying the resonator dimensions (pyramid side length, s).
Substrate Requirement: Requires high-purity Single Crystal Diamond (SCD) substrates (HPHT grade) for heteroepitaxial growth control and minimal defect incorporation.

# Technical Specifications

The following table summarizes the key experimental and performance parameters extracted from the research paper.

Parameter	Value	Unit	Context
Quality Factor (Q)	Up to 600	N/A	Measured for s = 1.5 µm pyramid structure
Mode Volume (V)	2.5(λ/n)³	N/A	Lowest simulated V, achieved for s = 1.05 µm structure
Resonant Wavelength (λ₀)	616.8	nm	Measured PL resonance peak
Refractive Index (n)	~2.4	N/A	Used in FDTD simulations
PECVD Power	1000	W	Microwave power supply
Growth Pressure	40	Torr	Chamber pressure
Substrate Temperature	760	°C	Measured via pyrometer
Gas Flow Ratio (CH₄:H₂)	1:100 (4:400)	sccm	Optimized for V₁₀₀ > V₁₁₁ pyramid formation
Growth Time	90	minutes	Total deposition time
Diamond Raman FWHM	2.60 ± 0.11	cm^-1	High quality of grown resonator material
Initial Ti Mask Layer	15	nm	Used for defining the SiO₂ template
SiO₂ Mask Thickness	300	nm	Patterned mask used for templated growth

# Key Methodologies

The experiment relies on precise surface preparation, advanced lithography, and tightly controlled MPCVD parameters to achieve the desired heteroepitaxial pyramid structures.

Substrate Cleaning: HPHT Single Crystal Diamond (SCD) substrate cleaned rigorously using refluxing acids (Nitric:Perchloric:Sulfuric) followed by boiling piranha mixture (Sulfuric Acid:Hydrogen Peroxide).
Template Fabrication (Mask Deposition): 15 nm Titanium (Ti) layer deposited via electron-beam evaporation, followed by the spin-on deposition of a 300 nm silica (SiO₂) film.
Patterning: Electron-Beam Lithography (EBL) used to define aperture regions (200 nm to 400 nm diameters) in the silica film.
Mask Etching: Unexposed Ti removed via Reactive Ion Etching (RIE) using Ar-Cl plasma to finalize the templated growth mask.
PECVD Growth: Diamond grown using Microwave PECVD at high power (1000 W) and controlled temperature (760 °C). The high H₂:CH₄ ratio (100:1) and pressure (40 Torr) were optimized to ensure the relative growth rate of the {100} faces was greater than {111} faces (V₁₀₀ > V₁₁₁), directing the formation of square pyramid structures.
Isolation Etch: The remaining patterned silica mask was removed using a Hydrofluoric Acid (HF) wet etch, creating an undercut structure below the pyramid posts to provide crucial optical isolation from the bulk substrate.

# 6CCVD Solutions & Capabilities

6CCVD provides the specialized materials and advanced fabrication services required to replicate this groundbreaking research and scale similar quantum photonic integration projects. Our commitment to material purity and geometric precision directly addresses the stringent demands of epitaxial growth and resonator design.

Applicable Materials

To replicate and advance the templated MPCVD growth of diamond optical resonators, researchers require the highest quality starting materials.

Application Requirement	6CCVD Recommended Solution	Technical Advantage
Starting Template (High-purity, low-defect SCD)	Optical Grade Single Crystal Diamond (SCD)	Provides the epitaxial template integrity necessary to minimize twinning and structural defects, resulting in high-Q structures (Ra < 1 nm polishing).
Dopant Source Control (In situ NV/SiV)	Custom Doped MPCVD Films	We offer control over nitrogen or silicon doping precursors to achieve specific concentrations of NV centers or SiV centers (or both), enabling deterministic or delta-doping for optimal emitter placement.
Alternate Structures (e.g., microdisks, pillars)	Polycrystalline Diamond (PCD) & BDD	Our PCD material allows for large-area, cost-effective fabrication of complex arrays. Boron-Doped Diamond (BDD) can be supplied for electro-optical tuning applications.

Customization Potential

The success of templated growth relies heavily on precise mask geometry and material integration. 6CCVD’s in-house capabilities ensure seamless integration into complex nanofabrication workflows.

Geometry and Dimensions: We offer custom laser cutting and shaping services to match any experimental template size, delivering plates and wafers up to 125 mm (PCD) and large-area SCD necessary for array fabrication.
Precision Layer Thickness: Researchers can specify diamond film thicknesses from 0.1 µm up to 500 µm for SCD and PCD, guaranteeing precise control over the height (h) of the supporting post and the resonator structure.
Advanced Surface Preparation: Epitaxial growth quality depends critically on the substrate surface. 6CCVD guarantees ultra-low roughness polishing (Ra < 1 nm for SCD), ensuring the defect-free surface crucial for high-quality, pyramidal growth documented in the paper.
Integrated Metalization: The research utilized a 15 nm Ti adhesion layer for mask fabrication. 6CCVD offers extensive in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to define masks, contacts, or thermal dissipation layers without outsourcing.

Engineering Support

This research targets advanced Quantum Information Science and integrated photonics. 6CCVD’s in-house PhD team provides authoritative support for complex quantum diamond projects.

Material Selection & Recipe Tuning: Our experts can assist in tailoring material specifications—such as optimizing CVD conditions for specific growth rate ratios (V₁₀₀/V₁₁₁) or adjusting dopant concentrations—to achieve desired color center properties and photonic structures.
Fabrication Troubleshooting: We provide guidance on utilizing our customized SCD or PCD products within existing nanofabrication lines, particularly concerning RIE compatibility, EBL processing, and acid resistance for wet etching (like the critical HF undercut step).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We are ready to supply the foundation for your next generation of diamond quantum devices.

View Original Abstract

We utilize plasma-enhanced chemical vapor deposition through a patterned silica mask for templated diamond growth to create optical resonators. The pyramid-shaped structures have quality factors Q up to 600, measured using confocal photoluminescence spectroscopy, and mode volumes V as small as 2.5(λ/n)3 for resonances at wavelengths λ between 550 and 650 nm, and refractive index n, obtained using finite-difference time-domain simulations. Bright luminescence from nitrogen-vacancy and silicon-vacancy centers in the grown diamond is observed. The resonator design and fabrication technique obviates any etching of diamond, which preserves emitter properties in a pristine host lattice.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4961536

References

2013 - Optical Properties of Diamond
2014 - Quantum Information Processing with Diamond: Principles and Applications