Engineering quantum-coherent defects - The role of substrate miscut in chemical vapor deposition diamond growth
At a Glance
Section titled âAt a Glanceâ| 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 | Stanford University, University of California, Santa Barbara |
| Citations | 13 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research establishes a critical link between substrate miscut angle and the engineering of coherent Nitrogen-Vacancy (NV) center ensembles in Chemical Vapor Deposition (CVD) diamond, crucial for quantum applications.
- Optimal Miscut Range: An optimal miscut angle range of 0.66° < θ < 1.16° is identified for engineering coherent NV ensembles while preserving the desired step-flow growth mode.
- Miscut Controls Key Parameters: Substrate miscut is shown to linearly control the diamond growth rate and the bulk nitrogen incorporation density, consistent with step-edge dependent growth.
- Hillock Defect Control: The density of flat-topped hillock defects is found to be inversely proportional to the miscut angle. A quantitative model predicts a critical angle (θc) of 1.9(2)° above which hillock nucleation is suppressed.
- Enhanced Nitrogen Localization: Nitrogen incorporation is significantly enhanced (up to 30 times) at hillock defects compared to the bulk layer, opening a pathway for templating localized, high-density NV ensembles.
- Coherence Quality: NV centers localized within hillock defects exhibit good coherence, with an ESR linewidth (Î = 3 MHz) similar to single NV centers in the bulk layer, suggesting hillocks do not inherently compromise spin quality.
- Growth Mode Transition: Miscuts above ~1.66° cause the growth to transition into an undesirable step-bunching regime, resulting in surface roughening and anisotropic defects.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal Miscut Angle Range | 0.66 to 1.16 | degrees (°) | Range for coherent NV ensemble engineering. |
| Critical Miscut Angle (θc) | 1.9(2) | degrees (°) | Angle where hillock nucleation is suppressed. |
| Step Velocity (vs) | ~100 | pm/s | Calculated step velocity, constant across studied miscuts. |
| Hillock Formation Time (TH) | ~100 | ms | Time required for a hillock to stabilize against step suppression. |
| Hillock Density (Doped, θ=0°) | 1.5(5) x 106 | cm-2 | Normalized density (ĎH0) for 15N enriched sample. |
| Nitrogen Enhancement at Hillocks | Up to ~30 | times | Relative increase of 15N counts at hillock sites (SIMS). |
| NV Linewidth (Hillock Defects) | 3 | MHz | Linewidth (Î) measured via Optically Detected ESR (OD-ESR). |
| Electron Irradiation Energy | 145 | keV | Used to create vacancies for NV formation. |
| Electron Irradiation Fluence | ~1017 | e-/cm2 | Total fluence applied post-growth. |
| Substrate RMS Roughness | < 200 | pm | Initial polishing quality of the multi-angle substrate. |
| Growth Rate Regime | < 10 | nm/hr | Slow growth rate regime used for high-quality doping. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized homoepitaxial plasma-enhanced CVD on a specialized substrate, followed by post-growth processing and advanced characterization.
- Substrate Preparation: A single diamond substrate was polished to feature five discrete regions with miscut angles ranging from 0.16° to 1.66°. The surface quality was high (RMS roughness < 200 pm).
- CVD Conditions: Growth was performed at a constant temperature of 800°C and a pressure of 25 torr in the slow growth rate regime (< 10 nm/hr).
- Buffer Layer Growth (3 hours): An undoped buffer layer was grown using 0.1 sccm of 99.999% 12C enriched methane.
- Doped Layer Growth (6 hours): The nitrogen-doped layer was grown using 0.1 sccm isotopically purified methane and 5 sccm of 98% 15N enriched nitrogen.
- Cap Layer Growth (4 hours): The sample was capped with an undoped layer using 0.1 sccm isotopically purified methane.
- NV Creation: Post-growth, the diamond was irradiated with 145 keV electrons (fluence ~ 1017 e-/cm2) to create vacancies, followed by annealing in Ar/H gas at 800°C for 8 hours.
- Characterization:
- Growth Rate/Depth: Secondary Ion Mass Spectrometry (SIMS) measured 13C depletion to determine layer thickness (d0).
- Nitrogen Distribution: SIMS measured 15N concentration depth profiles and spatially resolved 15N maps to confirm localization at hillocks.
- Surface Morphology: Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to quantify hillock density and surface roughness.
- Spin Properties: Scanning Confocal Microscopy and Optically Detected Electron Spin Resonance (OD-ESR) were used to measure NV center density and coherence linewidth (Î).
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to precisely control NV density, localization, and coherence via substrate engineering is critical for scaling quantum technologies based on solid-state defects.
- Quantum Sensing (Ensemble-Based): Enables the reliable production of dense, homogeneous, and coherent NV ensembles required for high-sensitivity magnetometry, electrometry, and thermometry.
- Quantum Networks and Computing: Provides a method for engineering coherent, near-surface NV centers, which are essential for coupling spins to external quantum elements like photons and phonons.
- Diamond Device Fabrication: Control over miscut ensures high surface quality and morphology, which is necessary for maintaining high quality factors in diamond photonic and phononic cavities used in spin-photon and spin-phonon coupling schemes.
- Localized Defect Templating: The enhanced nitrogen incorporation at hillock defects offers a novel technique for templating highly localized, high-density NV ensembles, potentially useful for creating addressable arrays or integrated quantum circuits.
- Advanced Material Synthesis: Provides a robust, bottom-up method for controlling lattice quality and dopant density simultaneously in homoepitaxial CVD diamond films.
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