Effect of Reactive Ion Etching on the Luminescence of GeV Color Centers in CVD Diamond Nanocrystals

At a Glance

Metadata	Details
Publication Date	2021-10-23
Journal	Nanomaterials
Authors	S. A. Grudinkin, Nikolay A. Feoktistov, Kirill Bogdanov, М. А. Баранов, В. Г. Голубев
Institutions	Ioffe Institute, ITMO University
Citations	8
Analysis	Full AI Review Included

Technical Analysis and Documentation: GeV$^-$ Color Centers in CVD Diamond

Executive Summary

This documentation analyzes the research on using Reactive Ion Etching (RIE) to enhance the optical properties of Germanium-Vacancy (GeV$^-$) color centers in nanodiamonds (NDs). The findings directly support the need for high-purity, low-strain diamond materials, a core offering of 6CCVD.

Core Achievement: Successful reduction of inhomogeneous spectral broadening of GeV$^-$ Zero-Phonon Lines (ZPLs) by removing highly defective, strained surface regions via RIE in oxygen plasma.
Material Optimization: RIE reduced the Full Width at Half Maximum (FWHM) of the diamond Raman line from ~7 cm⁻¹ to ~5.5 cm⁻¹, confirming a significant narrowing of the internal strain distribution.
Defect Mitigation: The etching process effectively eliminated $sp^2$-hybridized carbon defects localized on the ND surface, resulting in a lower broadband photoluminescence background.
Quantum Relevance: The ability to narrow the ZPL and resolve fine spectral structure at 80 K is critical for developing indistinguishable solid-state photon emitters required for quantum information technologies.
Strain Imaging: Analysis of the ZPL fine structure provides a novel optical method to image and analyze the distribution of local uniaxial strain fields within CVD nanodiamonds.
6CCVD Value Proposition: This research validates the necessity of high-quality material and precise post-processing, capabilities 6CCVD provides at the wafer scale using low-strain Single Crystal Diamond (SCD) substrates.

Technical Specifications

Parameter	Value	Unit	Context
Target Color Center	Negatively Charged Germanium-Vacancy (GeV$^-$)	N/A	Solid-state photon emitter
Zero-Phonon Line (ZPL) Wavelength	~602	nm	Measured at 300 K
Diamond Raman Band FWHM (As-Grown)	~7	cm⁻¹	Indicative of strain distribution
Diamond Raman Band FWHM (Etched)	~5.5	cm⁻¹	21% reduction post-RIE
Initial Nanodiamond Size	250-350	nm	HFCVD grown crystallites
Final Nanodiamond Size	< 200	nm	Post-RIE treatment
RIE Microwave Power	250	W	Frequency 2.45 GHz
RIE Substrate Temperature	500-600	°C	Oxygen-Nitrogen Plasma
RIE Working Pressure	10	Torr	Oxygen-Nitrogen mixture (20/80 vol.%)
Low Temperature Measurement	80	K	Used to resolve ZPL fine structure
High Spectral Resolution	0.03 (0.8)	nm (cm⁻¹)	Used for ZPL fine structure analysis
Neutral NV Center (NV$^0$) ZPL	~575	nm	Increased intensity observed post-RIE at 80 K

Key Methodologies

The fabrication and post-processing involved a two-step approach utilizing Hot Filament Chemical Vapor Deposition (HFCVD) followed by Reactive Ion Etching (RIE).

HFCVD Growth and GeV$^-$ Incorporation:
- Substrate Preparation: Silicon substrate seeded with detonation nanodiamonds for nucleation.
- Germanium Source: Bulk crystalline germanium placed on the substrate holder served as the solid-state source for Ge atoms.
- Growth Parameters: Tungsten coil temperature maintained at 2000-2200 °C. Working pressure set to 40 Torr.
- Gas Composition: Hydrogen flow rate of 500 sccm with a 2% methane concentration.
Reactive Ion Etching (RIE) Post-Processing:
- Purpose: Selective removal of defective, $sp^2$-induced surface regions.
- Gas Mixture: Oxygen-Nitrogen mixture (20/80 vol.%).
- Power and Frequency: Microwave power of 250 W at 2.45 GHz.
- Temperature and Pressure: Substrate temperature maintained at 500-600 °C; reactor working pressure set to 10 Torr.
- Duration: Etching duration of diamond particles was approximately 15 minutes.
Characterization:
- Micro-Raman/PL: Measured in backscattering geometry using a Renishaw “InVia” spectrometer.
- Excitation: 488 nm laser focused to a ~2 µm spot.
- Cryogenic Setup: Linkam THMS 600 used for 80 K measurements.

6CCVD Solutions & Capabilities

The research highlights that minimizing lattice strain and surface defects is paramount for realizing high-performance quantum emitters. 6CCVD specializes in providing the high-quality, low-defect diamond substrates and precision processing required to scale this research from nanodiamond ensembles to integrated quantum devices.

Applicable Materials

To replicate or extend this research onto a scalable platform, 6CCVD recommends materials optimized for minimal intrinsic strain and high purity:

Optical Grade Single Crystal Diamond (SCD): Our high-purity SCD is the ideal host material for Group IV color centers (GeV$^-$ or SiV$^-$). It offers superior crystalline quality and ultra-low residual strain compared to nanodiamond ensembles, ensuring the narrowest possible ZPL linewidths for quantum applications.
Boron-Doped Diamond (BDD) Substrates: For applications requiring electrical control or sensing, BDD can be utilized as a conductive platform for integration, with precise doping levels controlled during the MPCVD growth process.

Customization Potential

The paper utilized RIE to achieve defect removal and size reduction. 6CCVD offers comprehensive post-processing capabilities essential for device integration:

Research Requirement	6CCVD Capability	Specification & Advantage
Precision Etching/Shaping	Advanced Plasma Etching & Laser Cutting	We offer custom etching services to create microstructures, waveguides, or precisely size plates/wafers, replicating the defect-removal benefits of RIE but on bulk SCD/PCD.
Wafer Scale Production	Large-Area PCD/SCD Plates	We supply plates and wafers up to 125mm (PCD) and large-area SCD, enabling scalable fabrication of quantum devices, moving beyond the limitations of nanodiamond handling.
Surface Quality	Ultra-Smooth Polishing	SCD surfaces polished to Ra < 1nm and inch-size PCD polished to Ra < 5nm, minimizing surface defects that contribute to strain and non-radiative recombination.
Electrical Integration	Custom Metalization	In-house deposition of Au, Pt, Pd, Ti, W, and Cu contacts for electrical readout, strain tuning (as referenced in related literature), or thermal management.
Custom Thickness	Flexible Thickness Control	SCD and PCD layers available from 0.1µm to 500µm, allowing researchers to select the optimal thickness for specific photonic integration or sensing requirements.

Engineering Support

6CCVD’s in-house PhD team provides authoritative professional support for advanced diamond projects:

Strain Engineering: We assist clients in selecting materials and post-growth treatments (e.g., high-pressure, high-temperature annealing) to minimize or intentionally engineer local strain fields, which is critical for spectral alignment of GeV$^-$ emitters.
Defect Control: Consultation on optimizing growth parameters (temperature, gas mixture, pressure) for deterministic creation and control of Group IV color centers (GeV$^-$ and SiV$^-$) in low-defect environments.
Integration Expertise: Support for integrating diamond materials into hybrid photonic structures, bio-sensing platforms, and quantum computing architectures.

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

View Original Abstract

The negatively charged germanium-vacancy GeV− color centers in diamond nanocrystals are solid-state photon emitters suited for quantum information technologies, bio-sensing, and labeling applications. Due to the small Huang-Rhys factor, the GeV−-center zero-phonon line emission is expected to be very intensive and spectrally narrow. However, structural defects and the inhomogeneous distribution of local strains in the nanodiamonds result in the essential broadening of the ZPL. Therefore, clarification and elimination of the reasons for the broadening of the GeV− center ZPL is an important problem. We report on the effect of reactive ion etching in oxygen plasma on the structure and luminescence properties of nanodiamonds grown by hot filament chemical vapor deposition. Emission of GeV− color centers ensembles at about 602 nm in as-grown and etched nanodiamonds is probed using micro-photoluminescence and micro-Raman spectroscopy at room and liquid nitrogen temperature. We show that the etching removes the nanodiamond surface sp2-induced defects resulting in a reduction in the broad luminescence background and a narrowing of the diamond Raman band. The zero-phonon luminescence band of the ensemble of the GeV− centers is a superposition of narrow lines originated most likely from the GeV− center sub-ensembles under different uniaxial local strain conditions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano11112814

References

2019 - Quantum Nanophotonics with Group IV Defects in Diamond [Crossref]
2019 - Colour Centre Generation in Diamond for Quantum Technologies [Crossref]
2016 - Quantum Nanophotonics in Diamond [Crossref]
2019 - Synthesis, Properties, and Applications of Fluorescent Diamond Particles
2021 - Quantum Computer Based on Color Centers in Diamond [Crossref]
2018 - Fluorescent Nanodiamonds: Past, Present, and Future [Crossref]
2017 - Vacancy-Impurity Centers in Diamond: Prospects for Synthesis and Applications [Crossref]
2020 - Building Blocks for Quantum Network Based on Group-IV Split-Vacancy Centers in Diamond [Crossref]
2019 - Fiber-Optic Quantum Thermometry with Germanium-Vacancy Centers in Diamond [Crossref]
2019 - Bottom up Engineering of Single Crystal Diamond Membranes with Germanium Vacancy Color Centers [Crossref]