Hybrid Group IV Nanophotonic Structures Incorporating Diamond Silicon-Vacancy Color Centers

At a Glance

Metadata	Details
Publication Date	2015-12-22
Journal	Nano Letters
Authors	Jingyuan Linda Zhang, Hitoshi Ishiwata, Thomas M. Babinec, Marina Radulaski, Kai Müller
Institutions	Université Claude Bernard Lyon 1, Justus-Liebig-Universität Gießen
Citations	49
Analysis	Full AI Review Included

Technical Documentation & Analysis: Hybrid Group IV Nanophotonic Structures for SiV^- Quantum Emitters

This document analyzes the requirements and achievements detailed in the research paper, focusing on the synthesis and fabrication of high-quality Silicon-Vacancy (SiV^-) color centers in diamond nanostructures. It highlights how 6CCVD’s advanced Microwave Plasma Chemical Vapor Deposition (MPCVD) capabilities directly support the replication and scaling of this critical quantum technology.

Executive Summary

Core Achievement: Successful synthetic incorporation of high-quality negatively charged Silicon-Vacancy (SiV^-) color centers into diamond nanostructures via MPCVD, eliminating the need for post-growth ion implantation or annealing.
Material Systems: Demonstration of two device architectures: Hybrid diamond-SiC structures (nanowires and microdomes) and Monolithic all-diamond nanopillar arrays grown homoepitaxially on bulk diamond substrates.
Quantum Performance: Monolithic all-diamond nanopillars exhibit narrow linewidths (FWHM 28.3 GHz / 117 µeV) and small inhomogeneous broadening at 5 K, critical requirements for quantum computation and networking.
Doping Control: SiV^- centers were vertically positioned within a thin (~10 nm) diamond layer at a chosen depth, offering precise control over emitter location.
Growth Method: Utilized molecular diamond seeds (diamondoids) for nucleation and high-purity MPCVD growth, incorporating Si atoms diffused from nearby SiC plasma etching.
Device Scaling Potential: The demonstrated low strain and narrow linewidths in monolithic structures open opportunities for large arrays of individually addressable quantum emitters for quantum simulations and solid-state quantum memory.

Technical Specifications

The following table summarizes the key material and performance parameters achieved in the fabrication of SiV^- nanophotonic structures.

Parameter	Value	Unit	Context
SiV^- Zero Phonon Line (ZPL)	738	nm	Room Temperature PL emission peak
Low Temperature Operation	5	K	Required for observing four distinct, unstrained SiV^- lines
Monolithic Film Thickness	70	nm	Homoepitaxial SiV^- doped diamond layer
SiV^- Vertical Control	~10	nm	Thickness of the SiV^- doped layer at chosen depth
Nanopillar Diameter (Smallest)	115 - 130	nm	Used for g⁽²⁾(t) measurements
Nanopillar Height	150	nm	Monolithic all-diamond structures
FWHM (150 nm pillar, strongest transition)	28.3 (or 0.0513)	GHz (nm)	Corresponds to 117 µeV
Mean Lifetime (τ₁)	1.177 ± 0.064	ns	Comparable to single SiV^- centers in bulk diamond
Estimated SiV^- Doping Density	5×10¹⁵	cm^-3	Estimated density in 130 nm nanopillars
Spectrometer Resolution Limit	4.04	GHz	Limits measured linewidth of PL measurements

Key Methodologies

The research relies heavily on precise MPCVD control and advanced nanofabrication techniques.

CVD Growth Recipe (SiV^- Doping)

Substrate Preparation: Bulk 4H-SiC, 3C-SiC(100) thin films on Si(100), or Bulk Diamond (Type Ib) used as substrates.
Surface Functionalization: Substrate exposed to O₂ plasma (400 mTorr, 100 W, 5 min) to generate an oxide layer (2-5 nm).
Seeding: Substrate soaked in toluene solution containing 1mM 7-dichlorophosphoryl[1(2,3)4]pentamantane (a diamondoid seed).
Nucleation Step (MPCVD):
- Gas Mixture: H₂: 5 sccm, CH₄: 10 sccm, Ar: 90 sccm.
- Temperature/Power: 450 °C substrate temperature, 300 W microwave power.
- Pressure/Time: 23 Torr, ~20 min.
Growth Step (MPCVD):
- Gas Mixture: H₂: 300 sccm, CH₄: 3-7.5 sccm (1-2.5% CH₄ in H₂).
- Temperature/Power: 830 °C substrate temperature, 1300 W microwave power.
- Pressure: 30 Torr.
- Si Incorporation: SiV^- centers are incorporated during growth via diffusion of Si atoms from the plasma etching of the SiC substrate (or SiC placed near the diamond substrate for homoepitaxy).

Nanofabrication Sequence (Monolithic Nanopillars)

Homoepitaxial Growth: 70 nm SiV^- doped diamond film grown on bulk diamond.
Adhesion Layer: 5 nm HfO₂ deposited via Atomic Layer Deposition (ALD) to facilitate metal adhesion.
Mask Definition: Electron-beam lithography (EBL) using bilayer positive resist PMMA.
Hard Mask Evaporation: Gold (Au) evaporated onto the patterned resist.
Lift-off: PMMA and excess metal removed.
Pattern Transfer: Inductively Coupled Plasma (ICP) Reactive Ion Etching (RIE) used to transfer the nanopillar array pattern into the diamond film, etching past the SiV^- layer.
Mask Removal: Gold hard mask and HfO₂ adhesion layer removed using wet etching (gold etch and piranha clean).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity, custom diamond materials and advanced fabrication services required to replicate and advance this research in quantum photonics. Our expertise in MPCVD thin films ensures the low strain and high material quality necessary for stable SiV^- centers.

Applicable Materials

To achieve the low strain and high optical quality demonstrated in the monolithic nanopillar arrays, 6CCVD recommends the following materials:

6CCVD Material	Specification	Application Context
Optical Grade SCD	High Purity (Type IIa equivalent), N < 1 ppb.	Ideal substrate for low-strain homoepitaxial growth of SiV^- films, minimizing inhomogeneous broadening.
Custom SCD Thin Films	Thickness: 0.1 µm to 500 µm (e.g., 70 nm specified in paper).	Precise control over the thickness of the SiV^- doped layer for optimal emitter positioning and device integration.
PCD Substrates	Plates/wafers up to 125 mm diameter.	For scaling hybrid SiC/diamond structures or large-area monolithic arrays beyond typical bulk SCD sizes.

Customization Potential

6CCVD’s in-house capabilities directly address the specific material and fabrication requirements of this nanophotonics research:

Custom Dimensions: We supply high-purity SCD substrates and films in custom sizes, supporting wafer-scale processing up to 125 mm (PCD) or large-area SCD plates, enabling scaling of nanopillar arrays.
Precise Thickness Control: We guarantee the required 70 nm film thickness (or thinner/thicker films) with high uniformity, essential for controlling the vertical position of the SiV^- layer.
Advanced Metalization Stacks: The paper utilized an Au/HfO₂ hard mask stack. 6CCVD offers internal metalization services including Au, Pt, Pd, Ti, W, and Cu deposition, allowing researchers to define custom hard masks or electrical contacts directly on the diamond film. We can replicate the HfO₂ adhesion layer requirement.
Surface Preparation: We provide ultra-smooth polishing (Ra < 1 nm for SCD) necessary for subsequent high-resolution electron-beam lithography (EBL) and low-defect homoepitaxial growth.

Engineering Support

6CCVD’s in-house PhD team specializes in defect engineering and quantum material integration. We offer consultation services to assist researchers in:

SiV^-/NV^- Integration: Optimizing MPCVD recipes for controlled, low-strain incorporation of SiV^- or NV^- centers during growth, crucial for achieving single-emitter isolation (as the paper noted the need to reduce doping density below 5×10¹⁵ cm^-3).
Nanophotonic Fabrication: Advising on material selection (e.g., substrate orientation, surface termination) to improve yield and quality during subsequent nanofabrication steps like EBL and ICP RIE etching of diamond nanopillars.
Strain Management: Selecting optimal diamond growth parameters and substrate types to minimize lattice mismatch and strain-induced spectral shifting, particularly relevant for hybrid diamond-SiC projects.

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

View Original Abstract

We demonstrate a new approach for engineering group IV semiconductor-based quantum photonic structures containing negatively charged silicon-vacancy (SiV(-)) color centers in diamond as quantum emitters. Hybrid diamond-SiC structures are realized by combining the growth of nano- and microdiamonds on silicon carbide (3C or 4H polytype) substrates, with the subsequent use of these diamond crystals as a hard mask for pattern transfer. SiV(-) color centers are incorporated in diamond during its synthesis from molecular diamond seeds (diamondoids), with no need for ion-implantation or annealing. We show that the same growth technique can be used to grow a diamond layer controllably doped with SiV(-) on top of a high purity bulk diamond, in which we subsequently fabricate nanopillar arrays containing high quality SiV(-) centers. Scanning confocal photoluminescence measurements reveal optically active SiV(-) lines both at room temperature and low temperature (5 K) from all fabricated structures, and, in particular, very narrow line widths and small inhomogeneous broadening of SiV(-) lines from all-diamond nanopillar arrays, which is a critical requirement for quantum computation. At low temperatures (5 K) we observe in these structures the signature typical of SiV(-) centers in bulk diamond, consistent with a double lambda. These results indicate that high quality color centers can be incorporated into nanophotonic structures synthetically with properties equivalent to those in bulk diamond, thereby opening opportunities for applications in classical and quantum information processing.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acs.nanolett.5b03515