Electrical stimulation of non-classical photon emission from diamond color centers by means of sub-superficial graphitic electrodes

At a Glance

Metadata	Details
Publication Date	2015-10-29
Journal	Scientific Reports
Authors	Jacopo Forneris, Paolo Traina, Daniele Gatto Monticone, Giampiero Amato, Luca Boarino
Institutions	Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Rudjer Boskovic Institute
Citations	27
Analysis	Full AI Review Included

Technical Analysis: Electrical Stimulation of Non-Classical Photon Emission in MPCVD Diamond

This documentation analyzes the research paper detailing the fabrication and characterization of single-crystal diamond (SCD) devices utilizing sub-superficial graphitic electrodes for the electrical stimulation of single-photon emitters (color centers). This methodology validates MPCVD diamond as a robust platform for integrated, electrically-driven quantum light sources.

Executive Summary

Application Focus: Demonstrates the feasibility of electrical stimulation (Electroluminescence, EL) of isolated diamond color centers for creating compact, solid-state, on-demand single-photon sources (SPS) crucial for quantum communication.
Material Basis: Experiments utilized high-purity, Type-IIa Single-Crystal CVD Diamond (“Detector Grade,” N < 5 ppb, B < 1 ppb) as the insulating host material.
Novel Fabrication: Conductive graphitic electrodes were fabricated ~3 µm below the diamond surface using focused 6 MeV C³⁺ ion microbeam writing, followed by high-temperature vacuum annealing (950 °C).
Electrical Performance: Device operation showed a significant current injection threshold at V_a ~ 150 V, transitioning into a stable, high-current (up to 30 µA) regime governed by Poole-Frenkel conduction.
Quantum Verification: Non-classical light emission was confirmed from isolated electroluminescent spots via second-order autocorrelation measurements, achieving a zero-delay coincidence value (C_N(0)) of 0.51 ± 0.01.
Strategic Advantage: This technique simplifies device fabrication compared to complex p-i-n junction methods, enabling precise, localized electrical addressing of defects (likely NV⁰ centers) at predetermined depths and locations.

Technical Specifications

The following hard data points were extracted from the device fabrication and performance analysis:

Parameter	Value	Unit	Context
Substrate Material	Type-IIa Single Crystal CVD Diamond	-	”Detector Grade”
Nominal N Concentration	< 5	ppb	Substitutional Nitrogen
Nominal B Concentration	< 1	ppb	Substitutional Boron
Ion Beam Species	C³⁺	-	Used for electrode writing
Ion Beam Energy	6	MeV	High energy ion implantation
Ion Fluence (Target)	~4 x 10¹⁶	cm^-2	Required for graphitization threshold
Electrode Burial Depth	~3	µm	Below the diamond surface
Electrode Spacing	~10	µm	Gap between parallel electrodes
Electrode Dimensions	10 x 200	µm²	Width x Length
Annealing Temperature	950	°C	Vacuum, 2 hours
Critical Voltage Threshold (V_a)	~150	V	Onset of high-current injection / EL
Maximum Applied Bias	240	V	Used for EL spectroscopy
Maximum Current (High Regime)	~30	µA	Observed at +200 V bias
Non-Classical Emission (g²(0))	0.51 ± 0.01	-	Normalized zero-delay coincidence
Observed ZPL (NV⁰)	575	nm	Zero Phonon Line (PL Spectrum)
Observed EL Peaks	565, 580	nm	Attributed to interstitial/vacancy defects
Autocorrelation Width (α^-1)	143 ± 5	ns	Characteristic temporal width

Key Methodologies

The experiment successfully combined high-energy ion implantation, high-temperature thermal processing, and advanced nanofabrication techniques to create the electroluminescent device:

Material Selection: Use of type-IIa single-crystal CVD diamond characterized by extremely low concentrations of nitrogen and boron (sub-ppb range).
Graphitic Electrode Definition (Ion Microbeam): Focused 6 MeV C³⁺ ion beam was raster-scanned along linear paths to introduce radiation-induced structural damage ~3 µm below the surface.
Graphitization: The highly damaged channels were converted into conductive, sub-superficial graphitic electrodes by annealing the sample in vacuum at 950 °C for 2 hours.
Surface Cleanup: Conductive surface residues were removed via oxidation (air, 400 °C, 30 min) and oxygen plasma exposure (30 min).
Contact Exposure (FIB): A 30 keV Ga⁺ Focused Ion Beam (FIB) was used to mill trenches, exposing the ends of the buried graphitic channels at the diamond surface.
Metalization: A 60 nm thick Ag layer was deposited through a patterned mask onto the exposed channel endpoints to facilitate external wire-bonding and current injection.
Characterization: Electrical current-voltage (I-V) characteristics, photoluminescence (PL) mapping (532 nm excitation), electroluminescence (EL) mapping (215 V bias), and Hanbury Brown and Twiss interferometry were performed to verify single-photon emission.

6CCVD Solutions & Capabilities

6CCVD provides the ultra-high purity materials and precision engineering services necessary to replicate, optimize, and scale the production of electrically-stimulated quantum light sources described in this research.

Applicable Materials

To replicate and extend this research, 6CCVD recommends materials optimized for quantum applications:

Optical Grade Single Crystal Diamond (SCD): Required for achieving the low background noise and efficient defect incorporation necessary for SPS. Our high-purity SCD minimizes intrinsic defects and substitutional nitrogen/boron (<1 ppb available upon request), providing a clean host lattice for targeted color center generation (e.g., NV, SiV, GeV).
Substrates for Integration: SCD plates/wafers are available up to 500 µm thickness (standard) and substrates up to 10 mm, ensuring ample depth for MeV ion implantation and subsequent surface integration of optics.

Customization Potential

The experimental design relies heavily on precise geometry, deep implantation, and specialized contacts. 6CCVD directly supports these requirements:

Device Requirement	6CCVD Capability	Research Impact & Optimization
High-Precision Geometry	Custom Dimensions & Laser Cutting: We provide wafers/plates up to 125 mm (PCD) and offer micron-resolution laser shaping and dicing services.	Facilitates the creation of complex electrode arrays (as suggested in the Discussion) and precise alignment features for microbeam lithography.
Optical Interface Quality	Ultra-Smooth Polishing: Achieved surface roughness of R_a < 1 nm (SCD).	Essential for minimizing light scattering losses and maximizing the efficiency of integrated photonics, such as solid immersion lenses (SILs) or nanowires (as referenced in the paper).
Conductive Contacts	Custom Metalization: We offer internal deposition of standard stacks including Ti/Pt/Au, W, Cu, and Pd. While the paper used Ag, 6CCVD can provide optimized refractory or precious metal stacks for superior adhesion and lower resistance ohmic contact on FIB-exposed graphitic regions.	Ensures reliable, low-resistance interfaces crucial for stable, high-voltage operation (>200 V) and long device lifetimes (>200 hours stability demonstrated).
Material Scale-Up	Large-Area MPCVD Production: Our capability to grow large-area SCD wafers enables the transition from lab-scale prototypes to industrial arrays of quantum devices.	Supports the parallel fabrication of elaborated electrode arrays with sub-micrometric resolution.

Engineering Support

6CCVD’s in-house PhD team provides specialized engineering support for solid-state quantum projects. We assist clients with:

Material Selection: Guiding researchers on the optimal purity and crystal orientation for specific color center incorporation (e.g., maximizing NV⁰ or SiV yield via controlled doping or implantation).
Post-Processing Optimization: Advising on thermal annealing recipes crucial for graphitization recovery and defect charge state control, replicating the essential 950 °C vacuum treatment.
Integrating Fabrication Steps: Consulting on how to integrate high-energy implantation (MeV) and subsequent contact definition (FIB/metalization) onto the SCD platform efficiently.

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/srep15901