Silicon-vacancy color centers in phosphorus-doped diamond

At a Glance

Metadata	Details
Publication Date	2020-03-09
Journal	Diamond and Related Materials
Authors	Assegid M. Flatae, S. Lagomarsino, Florian Sledz, Navid Soltani, Shannon S. Nicley
Institutions	Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, University of Florence
Citations	24
Analysis	Full AI Review Included

Executive Summary

This study successfully demonstrates the creation and optical characterization of Silicon-Vacancy (SiV) color centers in phosphorus-doped (n-type) single-crystal diamond, paving the way for electrically driven quantum devices.

Core Achievement: First observation of single-photon emission (SPE) from SiV centers in P-doped diamond, confirmed by an anti-bunching measurement (g²(0) = 0.3).
Integration Advantage: Utilizing n-type diamond allows for simpler device architectures, such as Schottky diodes, for electrical excitation, avoiding the complexity of p-i-n junctions.
Background Suppression: The critical challenge of fluorescence background (due to doping, nitrogen, and ion damage) was significantly suppressed, enabling high spectral quality SPE.
Critical Parameter: Nitrogen concentration in the P-doped diamond is the most critical factor; it must be maintained below 1 ppb in the technical gases during CVD growth.
Methodology: SiV centers were created via Si-ion implantation (fluences 10⁷-10¹⁴ cm^-2) into MWPECVD-grown P-doped diamond films, followed by high-vacuum annealing (1200 °C).
Optimal Conditions: Single-photon emitters were obtained at low Si-ion implantation fluences (~10⁷ cm^-2), where clustering of SiV centers is minimized.

Technical Specifications

Parameter	Value	Unit	Context
SiV Excited-State Lifetime	1.0	ns	Measured in low-fluence implanted region (Sample A)
Single-Photon Purity (g²(0))	0.3	Dimensionless	Measured under pulsed excitation (must be < 0.5 for SPE)
SiV Zero-Phonon Line (ZPL)	~737	nm	Room temperature emission peak
Measured Photon Count Rate (I_∞)	1.576 ± 0.035 x 10³	cps	Background corrected count rate at saturation
Corrected Photon Count Rate	~4 x 10⁵	cps	Estimated maximum rate accounting for light trapping/setup efficiency
Si-Ion Implantation Fluence (SPE)	~10⁷	cm^-2	Fluence required to achieve well-separated single emitters
Si-Ion Implantation Depth	< 200	nm	Shallow implantation achieved using Al metal foils
SiV FWHM (Single Emitter)	7.6	nm	Full-width at half-maximum of the ZPL
Required N₂ Concentration	< 1	ppb	Target nitrogen impurity level in CVD growth gases
Annealing Temperature	1200	°C	High-vacuum (~10^-7 mbar) activation of SiV centers

Key Methodologies

The SiV color centers were created in P-doped single-crystal diamond films grown via Microwave Plasma-Enhanced Chemical Vapor Deposition (MWPECVD).

1. Diamond Growth (MWPECVD)

Substrates: High-Pressure High-Temperature (HPHT) diamond, primarily (111) oriented.
Dopant Source: Phosphine (PH₃).
Reactors: In-house built 2.45 GHz MWPECVD reactor (Sample A) or ASTeX PDS17 reactor (Samples B, C).
Gas Composition and Parameters:

Sample	PH₃/CH₄ Ratio	CH₄ Concentration (in H₂)	Deposition Temperature	Pressure
A	4300 ppm (Constant)	0.09 %	940 °C	160 Torr
C	5000 ppm (Constant)	0.15 %	1000 °C	140 Torr
B	0 to 20000 ppm (Gradient)	0.15 %	1000 °C	140 Torr

Purity Control: H₂ and CH₄ gases were filtered to less than 1 ppb (9 N) purity to minimize nitrogen incorporation, which is crucial for background suppression.

2. SiV Center Creation

Implantation System: 3 MeV Tandetron accelerator (HVEE 860 Negative Sputter Ion Source).
Ion Species: Si-ions (Si⁺, Si²⁺, Si³⁺) accelerated in the MeV range.
Energy Control: Aluminum (Al) metal foils were used to decrease the ion energy to a few tens of keV, ensuring shallow implantation (expected depth ≤ 200 nm).
Fluence Range: Samples were implanted with five fluences ranging from ~10⁷ cm^-2 to ~10¹⁴ cm^-2.
Activation Annealing: Post-implantation annealing was performed in a custom designed furnace at 1200 °C under high-vacuum conditions (~10^-7 mbar) to activate the SiV centers.

3. Optical Characterization

Measurement Setup: Homemade confocal microscopy setup.
SPE Verification: Hanbury-Brown Twiss interferometer used to measure the 2^nd order intensity autocorrelation function g²(t).
Background Analysis: Background sources (primarily Nitrogen-Vacancy (NV) centers) were investigated using multiple laser excitations (532 nm, 647 nm, 656 nm, 690 nm). Background was found to increase with implantation fluence.

Commercial Applications

The successful integration of SiV quantum emitters into n-type diamond facilitates the development of electrically driven quantum photonic devices, offering significant advantages in scalability and integration.

Quantum Computing: Provides a scalable solid-state platform for quantum bits (qubits) and quantum memory components operating at room temperature.
Quantum Communication and Cryptography: Enables the creation of efficient, room-temperature single-photon sources (SPS) crucial for secure communication lines (Quantum Key Distribution, QKD).
Integrated Quantum Photonics: The ability to use simpler Schottky diode configurations (instead of complex p-i-n junctions) facilitates the monolithic integration of quantum emitters with diamond-based electronics and waveguides.
Precision Sensing: High-quality color centers can be used for precision measurements below the shot-noise limit, relevant for magnetic and temperature sensing.
Diamond Semiconductor Devices: Advances in high-purity, P-doped n-type diamond growth (required for low background) directly benefit the development of high-power, high-frequency diamond electronics.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.diamond.2020.107797

References

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