Engineering quantum-coherent defects - The role of substrate miscut in chemical vapor deposition diamond growth

At a Glance

Metadata	Details
Publication Date	2020-11-09
Journal	Applied Physics Letters
Authors	Simon A. Meynell, Claire A. McLellan, Lillian B. Hughes, Wenbo Wang, Tom E. Mates
Institutions	University of California, Santa Barbara, Stanford University
Citations	13
Analysis	Full AI Review Included

Engineering Quantum-Coherent Defects: The Role of Substrate Miscut in MPCVD Diamond Growth

Executive Summary

This research demonstrates precise control over Nitrogen-Vacancy (NV) center ensemble formation and coherence in MPCVD diamond by tuning the substrate miscut angle ($\theta$). 6CCVD leverages its expertise in high-purity Single Crystal Diamond (SCD) growth to enable replication and extension of these critical quantum engineering techniques.

Optimal Miscut Range: An optimal miscut angle range of $0.66^{\circ} < \theta < 1.16^{\circ}$ was identified for engineering coherent ensembles of NV centers, balancing growth rate and defect density.
Growth Mechanism Control: Substrate miscut dictates the density of step edges, confirming that diamond growth in the slow rate regime (< 10 nm/hr) proceeds via a step-flow mechanism.
Defect Templating Potential: Nitrogen incorporation (doping) is significantly enhanced (up to 30x) at hillock defects, opening a pathway for templating localized, high-density NV ensembles for quantum applications.
Hillock Density Model: Hillock defect density was found to be inversely proportional to the miscut angle, consistent with a step-edge dependent nucleation and suppression mechanism.
Coherence Preservation: NV ensembles localized within hillocks exhibit an ESR linewidth ($\Gamma$) of 3 MHz, similar to single NVs in the bulk doped layer, suggesting the hillock morphology does not inherently compromise NV quality.
Material Requirement: Replicating this work requires ultra-high purity, isotopically controlled SCD substrates with precise, custom miscut angles.

Technical Specifications

The following hard data points were extracted from the analysis of the MPCVD growth and characterization:

Parameter	Value	Unit	Context
Optimal Miscut Angle Range	0.66 to 1.16	°	For coherent NV ensemble engineering
CVD Growth Temperature	800	°C	Constant during buffer, doped, and cap layers
CVD Growth Pressure	25	torr	Constant during growth
Growth Rate Regime	< 10	nm/hr	Slow growth, step-flow mechanism dominant
Step Velocity (v_s)	~100	pm/s	Calculated from linear dependence of thickness on miscut
Hillock Formation Time (T_H)	~100	ms	Calculated based on critical angle ($\theta_{c}$)
Critical Miscut Angle ($\theta_{c}$)	1.9(2)	°	Angle at which hillock density approaches zero
Nitrogen Enhancement at Hillocks	Up to 30x	Counts	Relative increase in ¹⁵N concentration compared to bulk
ESR Linewidth ($\Gamma$)	3	MHz	Measured for NV ensembles localized within hillocks
Electron Irradiation Fluence	~10¹⁷	e^-/cm²	Post-growth treatment for vacancy creation
Substrate RMS Roughness	< 200	pm	Polishing quality of the multi-angle substrate

Key Methodologies

The experiment utilized a three-step homoepitaxial MPCVD growth process on a multi-angle (100) SCD substrate, followed by post-processing to activate the NV centers.

Substrate Preparation: A single (100) SCD substrate was polished to five discrete miscut regions, ranging from $| \theta | = 0.16^{\circ}$ to $1.66^{\circ}$. RMS roughness was maintained at < 200 pm.
Buffer Layer Growth:
- Duration: 3 hours.
- Gas: 0.1 sccm of 99.999% ¹²C enriched isotopically purified methane.
- Purpose: Establish high-quality homoepitaxy.
Nitrogen Doped Layer Growth (In-Situ Doping):
- Duration: 6 hours.
- Gases: 0.1 sccm isotopically purified methane + 5 sccm of 98% ¹⁵N enriched nitrogen.
- Purpose: Introduce the NV precursor (Nitrogen) into the lattice.
Cap Layer Growth:
- Duration: 4 hours.
- Gas: 0.1 sccm isotopically purified methane.
- Purpose: Protect the doped layer and control NV depth localization.
Post-Growth Processing:
- Electron Irradiation: 145 keV electrons (total fluence ~ 10¹⁷ e^-/cm²) to create vacancies.
- Annealing: 8 hours at 800 °C in Ar/H gas (with a 16-hour ramp time) to mobilize vacancies and form NV centers.
Characterization: SIMS (depth profiling and spatial mapping of ¹³C and ¹⁵N), AFM, XRD, and Optically Detected Electron Spin Resonance (ESR) via scanning confocal microscopy.

6CCVD Solutions & Capabilities

This research highlights the critical need for highly controlled, custom-engineered diamond materials to advance quantum technologies. 6CCVD is uniquely positioned to supply the necessary SCD substrates and doped layers required to replicate and extend this work.

Applicable Materials

To achieve the high coherence and precise defect localization demonstrated in this paper, 6CCVD recommends the following materials:

Material Specification	6CCVD Capability	Application Context
Optical Grade SCD	SCD plates up to 500 µm thickness, high purity (low intrinsic defects).	Required for low magnetic noise environment and high qubit coherence.
Custom Miscut Substrates	SCD substrates with precise miscut control (e.g., $0.66^{\circ}$ to $1.16^{\circ}$) on the (100) face.	Essential for controlling step-flow growth, growth rate, and hillock density.
Isotopically Purified Diamond	SCD growth using high-purity ¹²C methane precursors.	Crucial for minimizing magnetic noise (e.g., ¹³C spin bath) and preserving qubit coherence.
In-Situ Doped Layers	Custom nitrogen (N) or boron (BDD) doping during growth, with thickness control from 0.1 µm to 500 µm.	Necessary for creating the NV precursor layer and controlling the depth of the quantum ensemble.

Customization Potential

The success of this research hinges on precise control over substrate geometry and doping profiles—core competencies of 6CCVD:

Miscut Engineering: 6CCVD provides custom-polished SCD substrates with specific miscut angles tailored to the customer’s desired step-flow regime and target hillock density (e.g., replicating the optimal $0.66^{\circ}$ to $1.16^{\circ}$ range).
Layer Thickness and Doping: We offer precise control over the thickness of buffer, doped, and cap layers (down to 0.1 µm resolution) and can incorporate specific dopants (N or B) at controlled concentrations to optimize NV formation yield and depth.
Large Area PCD: While this paper focused on SCD, 6CCVD can provide large-area Polycrystalline Diamond (PCD) plates up to 125 mm diameter, polished to Ra < 5 nm, for scaling up quantum sensing applications where large ensembles are required.
Advanced Polishing: We guarantee SCD surface roughness (Ra) < 1 nm, exceeding the < 200 pm RMS requirement of the paper, ensuring optimal surface quality for subsequent fabrication steps (e.g., photonic cavities).

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond quantum defects. We offer comprehensive consultation services to assist researchers and engineers in similar projects:

Material Selection for NV Engineering: Our experts can guide the selection of optimal miscut angles and doping concentrations to achieve specific NV density targets (e.g., high-density ensembles via hillock templating or low-density single NV layers).
Process Optimization: We provide technical support on how material properties (purity, miscut, surface termination) interact with post-processing steps like electron irradiation and annealing, critical for maximizing NV yield and coherence.
Custom Characterization: We can integrate specific characterization requirements (e.g., SIMS compatibility, specific thickness tolerances) into the material production workflow.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The engineering of defects in diamond, particularly nitrogen-vacancy (NV)\ncenters, is important for many applications in quantum science. A materials\nscience approach based on chemical vapor deposition (CVD) growth of diamond and\nin-situ nitrogen doping is a promising path toward tuning and optimizing the\ndesired properties of the embedded defects. Herein, with the coherence of the\nembedded defects in mind, we explore the effects of substrate miscut on the\ndiamond growth rate, nitrogen density, and hillock defect density, and we\nreport an optimal angle range between 0.66{\deg} < {\theta} < 1.16{\deg} for\nthe purposes of engineering coherent ensembles of NV centers in diamond. We\nprovide a model that quantitatively describes hillock nucleation in the\nstep-flow regime of CVD growth, shedding insight on the physics of hillock\nformation. We also report significantly enhanced incorporation of nitrogen at\nhillock defects, opening the possibility for templating\nhillock-defect-localized NV center ensembles for quantum applications.\n

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0029715