Optical activation and detection of charge transport between individual colour centres in diamond

At a Glance

Metadata	Details
Publication Date	2021-10-22
Journal	Nature Electronics
Authors	Artur Lozovoi, Harishankar Jayakumar, Damon Daw, György Vizkelethy, Edward S. Bielejec
Institutions	Sandia National Laboratories, Flatiron Health (United States)
Citations	54
Analysis	Full AI Review Included

Technical Documentation & Analysis: Charge Transport in Diamond NV Centers

This document analyzes the research paper “Optical activation and detection of charge transport between individual color centers in room-temperature diamond” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond capabilities, driving sales to researchers and engineers in quantum technology.

Executive Summary

The research successfully demonstrates controlled charge transport between individual, spatially separated Nitrogen-Vacancy (NV) centers in high-purity diamond, validating a critical mechanism for solid-state quantum computing and sensing.

Core Achievement: Articulation of confocal fluorescence microscopy and magnetic resonance protocols to induce and probe charge transport between discrete, engineered NV centers in bulk diamond.
Material Foundation: Experiments relied on electronic-grade Type 2a Single Crystal Diamond (SCD) with ultra-low intrinsic nitrogen concentration ($\le 5$ ppb) to minimize background defects.
NV Engineering: NV centers were precisely engineered $\sim 9-10$ µm deep using high-energy (20 MeV) focused $^{14}$N ion implantation, ensuring observations were free from surface effects.
Carrier Filtering: A spin-to-charge conversion (SCC) protocol was implemented as a carrier source filter, confirming that over 75% of trapped carriers originated from the source NV.
Giant Cross-Section: The observed hole capture cross-section ($\sigma_h \approx 3\times10^{-3}$ µm²) is orders of magnitude greater than typical ensemble values, attributed to unscreened Coulomb potentials in the high-purity lattice.
Quantum Bus Validation: The results open prospects for using free carriers as a quantum bus to mediate effective interactions between paramagnetic defects, supporting the development of solid-state quantum chips.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Diamond Substrate Purity	$\le 5$	ppb	Intrinsic Nitrogen concentration (Type 2a)
Ion Implantation Species	$^{14}$N	N/A	Used to create NV centers
Ion Implantation Energy	20	MeV	Focused ion beam from tandem accelerator
Implantation Depth (Source NV)	$\sim 10$	µm	Deep implantation to avoid surface effects
Implantation Depth (Target NV)	$\sim 9$	µm	Deep implantation to avoid surface effects
Inter-Defect Distance ($d$) Range	2.5 to 9.5	µm	Range tested for inverse square dependence
Experimental Hole Capture Cross Section ($\sigma_h$)	$\sim 3\times10^{-3}$	µm²	Observed value, orders of magnitude greater than ensemble
Onsager Trapping Radius ($r_t$)	$\sim 10$	nm	Calculated for room temperature
Green Excitation Wavelength	520	nm	Primary laser for photo-ionization (Source Park)
Readout Wavelength	594	nm	Low-power laser for charge-state preserving readout
Maximum Applied Electric Field ($E$)	$\approx 120$	mV µm^-1	Achieved via 60 V across 500 µm electrode gap
Annealing Temperature (Max)	1200	°C	Final step in six-step protocol for NV conversion

Key Methodologies

The experiment relied on precise material engineering and advanced optical control protocols:

Substrate Preparation: Electronic-grade Type 2a diamond (2×2×0.2 mm³) with intrinsic N concentration $\le 5$ ppb was used to ensure minimal background defects.
NV Center Engineering: A focused 20 MeV $^{14}$N ion beam was used to implant ions $\sim 10$ µm deep into the crystal, followed by a six-step annealing protocol culminating at 1200 °C to convert the implanted nitrogen into NV centers.
Surface Cleaning: The sample underwent a 1-hour tri-acid mixture treatment (nitric, sulfuric, perchloric) to remove graphite and impurities and provide oxygen termination.
Confocal Microscopy: A home-built confocal microscope with an oil-immersion objective (NA=1.3) was used, achieving diffraction-limited illumination ($\sim 0.5$ µm spot diameter).
Multi-Wavelength Excitation: Three continuous wave (CW) diode lasers (520 nm, 632 nm, 594 nm) were combined and pulsed for precise control over NV ionization, recombination, and readout.
Charge Transport Protocol: The ‘source’ NV was subjected to prolonged 520 nm excitation (Park) to generate carriers, and the resulting charge state change in the ‘target’ NV (separated by $d$) was monitored via 594 nm fluorescence readout.
Spin-to-Charge Conversion (SCC): MW excitation (2.87 GHz) was applied simultaneously with 520 nm and 632 nm lasers to selectively filter carriers originating from the source NV’s spin state, enabling high-fidelity carrier source identification.
External Field Application: Omega-shaped strip-line antennas were patterned onto the substrate to apply external electric fields, testing control over carrier transport dynamics.

6CCVD Solutions & Capabilities

This research highlights the critical need for ultra-high-purity, precisely engineered diamond substrates. 6CCVD is uniquely positioned to supply the necessary materials and customization services to replicate, extend, and commercialize this work.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Ultra-High Purity Substrates (Type 2a, N $\le 5$ ppb)	Optical Grade Single Crystal Diamond (SCD)	6CCVD guarantees intrinsic nitrogen concentration below 5 ppb, providing the pristine lattice required to achieve stable, isolated NV centers and observe unscreened Coulomb potential effects.
Deep Implantation Depth ($\sim 10$ µm)	Thick SCD Substrates (up to 500 µm)	We supply SCD wafers up to 500 µm thick, providing ample material depth for high-energy ion implantation necessary to place NV centers far from surface charge instabilities. Substrates up to 10 mm are available upon request.
High-Resolution Optical Access (NA=1.3)	Precision Polishing (Ra < 1 nm)	Our SCD wafers feature ultra-smooth surfaces (Ra < 1 nm), minimizing scattering and ensuring optimal optical coupling for high-NA objectives used in confocal microscopy and ODMR experiments.
Custom Electrode Patterning (MW Antenna, E-Field Control)	Integrated Metalization Services	6CCVD offers in-house deposition of standard metals (Ti, Pt, Au, Pd, W, Cu). We can pattern custom strip-line antennas or electrode geometries directly onto the diamond surface, facilitating external electric field control and microwave delivery.
Scalability and Custom Dimensions	Large Area PCD Wafers (up to 125 mm)	For scaling up quantum chip prototypes, 6CCVD provides Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, polished to Ra < 5 nm, suitable for large-scale integration of quantum devices.
Advanced Charge Control	Boron-Doped Diamond (BDD) Capabilities	For experiments requiring specific charge reservoir control or p-type doping, 6CCVD supplies custom Boron-Doped Diamond (BDD) films and substrates, enabling tailored electronic properties.

Engineering Support

The observed “giant” capture cross-sections and the successful use of carriers as a quantum bus are highly relevant for next-generation quantum technologies. 6CCVD’s in-house PhD team can assist with material selection for similar Solid-State Quantum Sensing and Quantum Information Processing projects, ensuring optimal substrate purity, orientation, and surface termination for advanced defect engineering.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41928-021-00656-z