Active and fast charge-state switching of single NV centres in diamond by in-plane Al-Schottky junctions

At a Glance

Metadata	Details
Publication Date	2016-11-16
Journal	Beilstein Journal of Nanotechnology
Authors	Christoph Schreyvogel, V. M. Polyakov, Sina Burk, Helmut Fedder, Andrej Denisenko
Institutions	University of Stuttgart, Leipzig University
Citations	8
Analysis	Full AI Review Included

Technical Analysis and Documentation: Fast Charge-State Switching of NV Centers in Diamond

Executive Summary

This research demonstrates a critical advance in solid-state quantum technology by achieving active and ultra-fast control over the charge state of single nitrogen-vacancy (NV) centers in diamond.

Ultra-Fast Control: Achieved high-frequency charge-state switching between all three NV states (NV⁺, NV⁰, NV⁻) on timescales as fast as τ < 10 ns, corresponding to a maximum switching frequency of >100 MHz.
Methodology: Utilizes a planar, two-dimensional aluminum (Al) Schottky-diode structure fabricated on a hydrogen-terminated (H-terminated) intrinsic MPCVD diamond surface.
Mechanism: Applying bias potential modulates the Fermi-level position relative to the NV charge transition levels via band bending in the depletion region.
Material Foundation: Success relies on high-purity, homoepitaxially grown intrinsic diamond material created via MWPECVD (Microwave Plasma Enhanced Chemical Vapor Deposition).
Quantum Application: The realized high-speed switching is three orders of magnitude faster than the hyperfine interaction rate (2.66 kHz), making this technology vital for high-fidelity quantum registers, long-lifetime storage using ¹³C atoms, and single-photon emitters for quantum communication.
Scalability: The planar diode architecture provides a scalable platform for addressing individual NV centers in larger quantum circuitry arrays.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Substrate Type	Ib (100)	N/A	Used as base for homoepitaxial growth
Epitaxial Layer Thickness	300	µm	Intrinsic, high-purity SCD grown via MWPECVD
Nitrogen Implantation Energy	5	keV	Used for creating near-surface NV centers
Mean NV Center Depth	8.2	nm	Critical for surface interaction and coupling
Nitrogen Ion Dose	10⁸	ions/cm²	Resulted in 10⁶-10⁷ cm⁻² NV sheet density
NV Formation Annealing	800	°C	2 hours in vacuum
Switching Transition	NV⁻ → NV⁺ or NV⁰ → NV⁺	N/A	Fastest discharge time constant, τ < 10 ns
Maximum Switching Frequency	>100	MHz	Theoretical max based on fastest transition
Charging Transition (NV⁺ → NV⁻)	≈1	MHz	Limited by T₁ ≈ 50 ns, T₂ ≈ 330 ns
Metal Contact Thickness	200	nm	Al (Schottky) and Au (Ohmic)
Applied Switching Potential	±15 to ±20	V	Used to drive charge state modulation
Excitation Laser	520	nm	Continuous wave (cw) green laser for PL detection
Diode Contact Dimensions	1 x 0.3	mm²	In-plane Schottky diode geometry

Key Methodologies

The experiment relies on precision fabrication, combining advanced MPCVD growth with controlled surface modification and metal deposition:

Intrinsic SCD Growth: A thick, high-ppurity intrinsic diamond epilayer (300 µm) was grown homoepitaxially onto a Type Ib (100) substrate using a MWPECVD reactor.
Surface Preparation & Termination: The epi-layer was mechanically polished to a surface roughness of Ra < 5 nm, followed by wet chemical cleaning to achieve Oxygen-termination (O-termination).
Near-Surface NV Creation: Nitrogen ions were implanted at 5 keV (resulting in 8.2 nm mean depth) with a dose of 10⁸ ions/cm² to create the required defect density.
Annealing: The sample was annealed at 800 °C in vacuum for 2 hours to promote vacancy mobility and the formation of stable NV centers.
2D Hole Channel Formation: The diamond surface was treated with a pure Hydrogen plasma (H-termination) in the MWPECVD reactor to induce a two-dimensional hole accumulation layer below the surface.
Schottky Diode Fabrication: Standard photolithography and thermal evaporation techniques were used to deposit 200 nm thick metal contacts: Aluminum (Al) for the Schottky contact (570 meV barrier height) and Gold (Au) for the Ohmic contact.
Channel Isolation: The conductive channel region was protected with photoresist while the surrounding surface was intentionally re-terminated via oxygen plasma (O-termination) to isolate the active device area.

6CCVD Solutions & Capabilities

This research validates the critical role of high-purity, expertly processed MPCVD diamond in achieving breakthrough speeds necessary for quantum technologies. 6CCVD is uniquely positioned to supply and engineer the core material components and advanced device structures required to replicate and scale this fast charge-state switching technology.

Applicable Materials

To replicate the high-fidelity charge state switching described, researchers require ultra-low-defect material suitable for subsequent precision implantation and surface modification.

Optical Grade SCD: 6CCVD Single Crystal Diamond (SCD) wafers are provided with intrinsic, high-purity layers up to 500 µm thickness, essential for creating the required 2D hole channel stability and isolating the NV centers from bulk defects.
High-Purity Substrates: We provide Type Ib or Type IIa (100) substrates necessary for homoepitaxial growth of the intrinsic diamond required for the MWPECVD process used in this paper.

Customization Potential

The success of the Schottky diode structure depends critically on precise metal contacts and well-controlled surface termination processes. 6CCVD provides comprehensive engineering services to support these requirements:

Research Requirement	6CCVD Custom Capability	Benefit to Quantum Device Engineering
Custom Metal Stacks (Al/Au)	In-house Metalization: Deposition of Au, Ti, Pt, Pd, W, and Cu. We can readily implement the required Al/Au stack thickness (200 nm) or alternative contacts (e.g., Ti/Pt/Au for enhanced adhesion/stability).	Rapid prototyping and fabrication of complex in-plane quantum devices and electrodes.
Planar Diode Geometry	Custom Dimensions & Laser Cutting: Plates/wafers up to 125mm (PCD) or custom-cut SCD samples. We utilize high-precision laser cutting for specific device geometries (like the 1 mm x 300 µm contacts) used in this work.	Enables scaling from small research samples (3 x 3 mm³) to full wafer-level quantum array manufacturing.
Ultra-Smooth Surface	Advanced Polishing: Our SCD material is polished to an industry-leading surface roughness of Ra < 1 nm, far surpassing the quality often required for sensitive near-surface quantum defects (8.2 nm depth used here).	Minimizes surface-related noise and degradation effects on near-surface NV centers, improving coherence and charge-state stability.
Passivation/Stability	Surface Engineering Support: Expertise in material handling and preparation for H-termination processes required to generate the essential 2D hole channel.	Assists researchers in implementing stable passivation techniques (like Al₂O₃ ALD film coverage mentioned in the paper) to mitigate device degradation during cycling.

Engineering Support

6CCVD’s in-house team of PhD material scientists and technical engineers is available to assist customers with projects related to NV charge state control and solid-state quantum registers. We specialize in optimizing MPCVD growth recipes to match the stringent purity and thickness specifications needed for near-surface defect creation and stable electrical/optical manipulation of single quantum emitters.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of critical components worldwide.

View Original Abstract

In this paper, we demonstrate an active and fast control of the charge state and hence of the optical and electronic properties of single and near-surface nitrogen-vacancy centres (NV centres) in diamond. This active manipulation is achieved by using a two-dimensional Schottky-diode structure from diamond, i.e., by using aluminium as Schottky contact on a hydrogen terminated diamond surface. By changing the applied potential on the Schottky contact, we are able to actively switch single NV centres between all three charge states NV + , NV 0 and NV − on a timescale of 10 to 100 ns, corresponding to a switching frequency of 10-100 MHz. This switching frequency is much higher than the hyperfine interaction frequency between an electron spin (of NV − ) and a nuclear spin (of 15 N or 13 C for example) of 2.66 kHz. This high-frequency charge state switching with a planar diode structure would open the door for many quantum optical applications such as a quantum computer with single NVs for quantum information processing as well as single 13 C atoms for long-lifetime storage of quantum information. Furthermore, a control of spectral emission properties of single NVs as a single photon emitters - embedded in photonic structures for example - can be realized which would be vital for quantum communication and cryptography.

Tech Support

Original Source

DOI: https://doi.org/10.3762/bjnano.7.165