Electroluminescence from a diamond device with ion-beam-micromachined buried graphitic electrodes

At a Glance

Metadata	Details
Publication Date	2015-01-06
Journal	Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Authors	J. Forneris, A. Battiato, D. Gatto Monticone, Federico Picollo, Giampiero Amato
Institutions	Istituto Nazionale di Fisica Nucleare, Sezione di Torino, National Interuniversity Consortium for the Physical Sciences of Matter
Citations	16
Analysis	Full AI Review Included

Technical Documentation: Electroluminescence from Buried Graphitic Electrodes in SCD Diamond

This document analyzes the electrical excitation of color centers in Single Crystal Diamond (SCD) via charge injection through buried graphitic electrodes, a technique highly relevant to the development of integrated quantum emitters. This research demonstrates the unique synergy between focused ion beam micro-machining and high-purity Chemical Vapor Deposition (CVD) diamond materials supplied by 6CCVD.

Executive Summary

This research successfully demonstrates Electroluminescence (EL) in high-quality CVD Single Crystal Diamond (SCD) using innovative buried electrodes fabricated by Deep Ion Beam Lithography (DIBL).

Material Foundation: The device relies on a detector-grade, intrinsic CVD SCD film grown on an HPHT substrate, ensuring the necessary purity for high-performance color centers.
Fabrication Technique: Conductive graphitic channels were written 3 µm below the diamond surface using 1.8 MeV He⁺ microbeam lithography, followed by high-temperature annealing.
Electrical Excitation: EL was achieved by exploiting current flow (associated with avalanche breakdown, > 200 V bias) between non-rectifying graphitic electrodes spaced by 10 µm.
Color Center Identification: Spectroscopic analysis confirmed strong EL emission from key defects, including the neutral Nitrogen-Vacancy (NV⁰) center (ZPL @ 575 nm) and A-band lattice dislocations.
Novel Emitters: The study highlights the successful electrical excitation of sharp-emission, low-phonon-sideband He-related defects (ZPLs @ 536.3 nm and 560.5 nm).
Application Relevance: This method confirms a scalable path toward fabricating electrically-driven, integrated single-photon emitters, crucial for advancing quantum optics and quantum cryptography devices.

Technical Specifications

Key material, processing, and performance parameters extracted from the research paper.

Parameter	Value	Unit	Context
Material Base	SCD (Type-Ib HPHT Substrate)	N/A	Detector-grade CVD single-crystal diamond
CVD Film Thickness	~40	µm	Intrinsic diamond homoepitaxial layer
Substrate Dimensions	4 x 4 x 0.4	mm³	Commercial starting material
Ion Beam Species	1.8 MeV	He⁺	Used for Deep Ion Beam Lithography (DIBL)
Ion Fluence	1.5 x 10¹⁷	cm^-2	Minimum required to exceed graphitization threshold
Electrode Depth	~3	µm	Below the diamond surface (Bragg’s peak location)
Inter-Electrode Gap	10	µm	Spacing of the buried graphitic channels
Annealing Process	> 900	°C	2 hours in vacuum (converts amorphized regions to graphite)
EL Turn-On Voltage	> 200	V	Corresponds to typical currents of ~100 nA
EL Mapping Bias Voltage	250	V	Voltage used for spatial mapping
NV⁰ Zero-Phonon Line (ZPL)	575	nm	Neutrally-charged Nitrogen-Vacancy center
He-Related ZPL (Sharp Peaks)	536.3, 560.5	nm	Appealing photophysical properties (low phonon sidebands)
A-Band Peak Center	435	nm	Broad peak attributed to lattice dislocations

Key Methodologies

The fabrication of the electroluminescent device relied on precise material selection and controlled ion-beam processing.

Sample Preparation: Growth of a ~40 µm thick intrinsic CVD single-crystal diamond film on a commercial 4x4x0.4 mm³ Type-Ib HPHT substrate.
Masking: A slowly thinning copper mask was deposited on the surface to accurately control the depth of the MeV ion Bragg’s peak.
Graphitic Channel Writing: Deep Ion Beam Lithography (DIBL) was performed using a scanning 1.8 MeV He⁺ microbeam (spot size ~10 µm) at a high fluence (1.5 x 10¹⁷ cm^-2). This creates amorphized channels approximately 3 µm deep.
Graphitization & Damage Recovery: The implanted sample was thermally annealed (2 hours, in vacuum, T > 900 °C) to convert the amorphized channels into nanocrystalline graphite electrodes.
External Contacts: Wire-bonding pads were formed by depositing 80 nm thick Cr/Al circular contacts (150 µm diameter) connected to the buried channels endpoints.
Characterization: Electroluminescence (EL) was excited by applying high voltage bias (up to 250 V) across the 10 µm inter-electrode gap, utilizing the resulting current flow (avalanche breakdown).
Optical Mapping: EL emission was spatially mapped using a confocal optical microscopy setup (100x objective, N.A. = 0.9) connected to a SPAD photon counter.

6CCVD Solutions & Capabilities

This research highlights the need for specialized CVD diamond material and precision fabrication techniques, aligning perfectly with 6CCVD’s core offerings for quantum and photonic applications.

Research Requirement	6CCVD Solution & Capability	Advantage for Replication/Extension
High-Purity Insulating Substrate	Optical Grade SCD (Single Crystal Diamond). Ultra-low nitrogen content (high intrinsic purity).	Essential starting material for ensuring high quantum efficiency of engineered color centers (NV, Si-V) and minimal parasitic luminescence.
Custom Thickness & Dimensions	Wafers/plates up to 125mm (PCD) or custom-cut SCD. Thickness control: SCD films from 0.1 µm up to 500 µm; Substrates up to 10mm.	Provides the necessary in-house flexibility to supply the specific 4x4 mm² dimensions and the required SCD film thickness (e.g., 40 µm) needed to precisely locate the DIBL Bragg peak.
Advanced Interconnects	Custom Metalization Services: Internal deposition capabilities for Au, Pt, Pd, Ti, W, and Cu.	Facilitates the integration of external electronics, allowing researchers to skip outsourcing the critical 80 nm Cr/Al (or alternative low-resistance) contact deposition steps.
Post-Processing Surface Quality	Precision Polishing: Achieves surface roughness Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.	Guarantees the necessary high-quality optical surface required for high Numerical Aperture (N.A. = 0.9) confocal microscopy light collection and maximum photon extraction efficiency.
Quantum Emitter Engineering	Boron-Doped Diamond (BDD) Capabilities. Custom BDD films and plates are available.	While this paper used intrinsic diamond, BDD provides an alternative route for charge injection, crucial for maximizing EL efficiency and controlling the charge state of NV centers (NV^- vs NV⁰).

Engineering Support

6CCVD specializes in providing high-purity CVD diamond optimized specifically for quantum applications. Our in-house PhD team offers comprehensive consultation on optimizing material selection, including nitrogen and silicon doping control, which is essential for maximizing the density and stability of electrically excitable defects like NV and Si-V centers utilized in this research. We help engineers define the optimal starting material to ensure device scalability and performance reliability.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.nimb.2014.12.036