Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-09-16 |
| Journal | Nanophotonics |
| Authors | Jan Fait, M. Varga, Karel HruĹĄka, Alexander Kromka, Bohuslav Rezek |
| Institutions | Czech Academy of Sciences, Institute of Physics, Czech Technical University in Prague |
| Citations | 5 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel, two-step fabrication and tuning method for diamond photonic crystal (PhC) slabs, overcoming the challenge of achieving nanoscale precision in structuring.
- Core Innovation: Spectral tuning of PhC leaky modes is achieved by depositing a thin, SiV-rich nanocrystalline diamond (NCD) layer onto a pre-patterned PhC slab, increasing the effective refractive index (Neff) and red-shifting the modes.
- Performance Achievement: The method successfully shifted the PhC modes by more than 100 nm to spectrally overlap with the Silicon Vacancy (SiV) center Zero-Phonon Line (ZPL) at 738 nm.
- Extraction Enhancement: A maximum Photoluminescence (PL) intensity enhancement factor of nine was achieved for the SiV ZPL without resonant excitation.
- Sensing Configuration: The SiV centers are intentionally located in the thin surface tuning layer (~60 nm thick), making them highly sensitive to changes in the surrounding environment, ideal for biosensing and gas detection.
- Fabrication Advantage: This approach avoids the need for nanometer-scale precision during the initial Electron Beam Lithography (EBL) and Reactive Ion Etching (RIE) steps, simplifying the manufacturing process.
- Versatility: The tuning method is adaptable to other diamond optical centers (e.g., NV, GeV centers) and various photonic structures (e.g., PhC cavities, nanobeams, nanopillars).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Emission Line (ZPL) | 738 | nm | Silicon Vacancy (SiV) center |
| Maximum PL Enhancement Factor | ~9 | Dimensionless | Observed using NA 0.4 and 0.5 objectives |
| Spectral Shift Achieved | >100 | nm | Shifted TE0 mode from 622 nm (original) to 757 nm (tuned) |
| Tuning Layer Thickness (Target) | ~58 | nm | Estimated via RCWA simulation |
| Tuning Layer Thickness (Actual) | ~60 | nm | Measured after deposition |
| Original PhC Lattice Constant (L) | 390 | nm | Maintained constant during tuning |
| Original Column Diameter (d) | 215 | nm | Increased to 335 nm after tuning layer deposition |
| Original Total Thickness (t) | 160 | nm | Increased to 220 nm after tuning layer deposition |
| TE0 Mode Coupling Efficiency Ratio | 1.22 | Dimensionless | TE0 mode coupling is 1.22x higher than TM0 mode |
| Excitation Wavelength | 442 | nm | He-Cd laser used for PL measurements |
Key Methodologies
Section titled âKey MethodologiesâThe PhC slabs were fabricated using a two-step CVD process combined with EBL and RIE.
1. Substrate Preparation and Original Layer Growth (SiV-Free NCD)
Section titled â1. Substrate Preparation and Original Layer Growth (SiV-Free NCD)â- Substrate: Quartz, seeded via ultrasonic agitation in nanodiamond colloidal dispersion.
- Reactor: Linear antenna Microwave (MW) plasma system (pulsed regime).
- Original Layer CVD Parameters:
- Deposition Time (t): 19 h
- Pressure (p): 10 Pa
- H2 Flow: 200 sccm
- CH4 Flow: 5 sccm
- CO2 Flow: 20 sccm
- MW Power (P): 2 x 1.7 kW
- Surface Temperature (T): ~540 °C
- Resulting Thickness: ~160 nm
2. PhC Patterning (EBL and RIE)
Section titled â2. PhC Patterning (EBL and RIE)â- Goal: Fabricate PhC structure with leaky modes intentionally blue-shifted from the 738 nm SiV ZPL.
- Process:
- EBL used to pattern poly(methyl methacrylate) (PMMA) resist (~100 nm thick).
- Gold mask (~70 nm thick) evaporated via lift-off process.
- RIE performed using capacitively coupled O2/CF4 plasma to etch the NCD layer.
- Metal mask removed by wet etching.
3. Spectral Tuning Layer Deposition (SiV-Rich NCD)
Section titled â3. Spectral Tuning Layer Deposition (SiV-Rich NCD)â- Reactor: Focused MW plasma reactor (Aixtron P6) using an ellipsoidal cavity resonator.
- Si Source: Pieces of common intrinsic Si wafer placed near the sample, partially etched by plasma to incorporate SiV centers.
- Tuning Layer CVD Parameters:
- Deposition Time (t): 15 min
- Pressure (p): 6 kPa
- H2 Flow: 300 sccm
- CH4 Flow: 3 sccm
- Power (P): 3 kW
- Temperature (T): ~820 °C
- Growth Rate: ~4 nm/min (Fast growth rate inherent to the system)
- Resulting Thickness: ~60 nm
4. Post-Processing (Surface Termination)
Section titled â4. Post-Processing (Surface Termination)â- Treatment: Oxygen plasma treatment was performed as a final step.
- Effect: Improves the PL intensity of SiV centers located near the diamond surface by altering the surface termination.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology, focusing on enhanced light extraction and surface-near placement of color centers in cost-effective NCD PhC slabs, is highly relevant for:
- Quantum Sensing and Metrology:
- High-performance gas detection (using angular shift of leaky modes).
- Biosensing applications, leveraging the stability of diamond and the surface proximity of SiV centers.
- Magnetometry (if adapted for NV centers).
- Quantum Optics and Information Processing:
- Fabrication of high-efficiency single-photon sources (SPS) and quantum light sources.
- Cost-effective fabrication of 2D PhC slabs using large-scale methods (e.g., nanoimprint or nanosphere lithography) followed by nanoscale tuning.
- Advanced Photonic Devices:
- Improved light collection efficiency devices requiring high emission rates.
- Adaptation of the tuning method for single-crystal diamond structures like PhC cavities and nanobeams, where dimensional deviations are common.
View Original Abstract
Abstract The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.