Optical–Microwave Pump–Probe Studies of Electronic Properties in Novel Materials
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-10-09 |
| Journal | physica status solidi (b) |
| Authors | Sándor Kollarics, András Bojtor, Kristóf Koltai, Bence G. Márkus, K. Holczer |
| Institutions | HUN-REN Centre for Energy Research, École Polytechnique Fédérale de Lausanne |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Broadband Microwave-Optical Spectroscopy using MPCVD Diamond
Section titled “Technical Documentation & Analysis: Broadband Microwave-Optical Spectroscopy using MPCVD Diamond”This document analyzes the requirements and achievements of the research paper “Optical-microwave pump-probe studies of electronic properties in novel materials” and maps them directly to the advanced material solutions provided by 6CCVD.
Executive Summary
Section titled “Executive Summary”The research successfully demonstrates the utility of combined microwave-optical pump-probe methods (ODMR and µ-PCD) for analyzing quantum spin centers and charge carrier dynamics, leveraging broadband Coplanar Waveguides (CPW) built on high dielectric substrates.
- Core Achievement: Development of two high-sensitivity spectrometers (ODMR and µ-PCD) utilizing CPW structures, overcoming the bandwidth limitations inherent in traditional microwave resonators.
- Material Validation: Successful ODMR mapping of Nitrogen-Vacancy (NV) centers in Type-II single crystal diamond, confirming diamond’s role as a critical platform for quantum sensing.
- Performance Metrics: The CPW design achieved efficient microwave coupling, demonstrating a power-to-magnetic field conversion factor comparable to a high Q-factor resonator (Q ≈ 4000).
- Broadband Operation: The CPW enabled frequency-swept ODMR experiments across a wide range (2.6 GHz to 3.2 GHz), essential for resolving complex spin transitions.
- Material Requirement: The methodology relies fundamentally on high-purity, precisely dimensioned Single Crystal Diamond (SCD) substrates, which 6CCVD specializes in manufacturing.
- Cryogenic Capability: The CPW setup was successfully integrated into a cryostat, confirming the viability of the diamond platform for low-temperature quantum and semiconductor studies (down to 77 K).
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental setup and results, highlighting the precision required for successful replication and extension of this research.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Sample Dimensions | 3 x 3 x 0.3 | mm | Single crystal Type-II |
| ODMR Excitation Wavelength | 532 | nm | Continuous Wave (CW) Laser |
| µ-PCD Excitation Wavelength | 527 | nm | Pulsed Laser |
| µ-PCD Pulse Energy | 150 | µJ | Used for charge carrier excitation |
| External Magnetic Field (Max) | 1.2 | T | Applied during ODMR measurements |
| ODMR Frequency Range (Map) | 2.6 - 3.2 | GHz | Demonstrated broadband operation |
| CPW Gap Separation | 250 | µm | Critical dimension for waveguide design |
| CPW Total Width | 6 | mm | Total dimension of the waveguide |
| MW Power to B-Field Conversion | 0.88 x 10-8 | T2/W | Achieved by the CPW structure |
| Equivalent Q-factor (CPW) | 4000 | Dimensionless | Comparison to classical resonators |
| Cryostat Vacuum Level | 10-6 | mbar | Required for cryogenic measurements |
Key Methodologies
Section titled “Key Methodologies”The experimental success hinges on precise material preparation and the integration of the diamond substrate into the custom CPW structure.
ODMR Spectroscopy on NV Centers in Diamond
Section titled “ODMR Spectroscopy on NV Centers in Diamond”- Material Selection: High-purity, single crystal Type-II diamond (3 x 3 x 0.3 mm) was used as the substrate for NV center studies.
- NV Center Creation: The diamond was processed via high-pressure high-temperature (HPHT) treatment, followed by 100 MeV electron irradiation (fluence 1017 e-/cm2) and subsequent annealing at 1000 °C to create stable NV centers.
- Microwave Delivery: Microwaves were fed into a 50 Ω terminated CPW via an amplifier (40 dB gain) to ensure efficient coupling to the NV centers in the diamond.
- Detection Scheme: Luminescence was collected and focused onto a spectrograph equipped with a photomultiplier tube and InGaAs detector, with the signal processed by a lock-in amplifier synchronized to the MW chopping frequency.
Microwave Detected Photoconductivity Decay (µ-PCD)
Section titled “Microwave Detected Photoconductivity Decay (µ-PCD)”- Sample Integration: A phosphorus-doped silicon wafer was placed directly onto the CPW structure.
- Carrier Excitation: A pulsed 527 nm laser (1 kHz repetition rate, 1.7 µs pulse width) was used to generate non-equilibrium charge carriers.
- MW Probing: A microwave oscillator probed the sample, and the reflected waves were processed through a directional coupler and a custom MW bridge (including a magic tee and phase shifter) to nullify DC reflection.
- Signal Acquisition: The resulting RF signal was amplified (15 dB gain), downconverted by an IQ mixer, and digitized by a 200 MHz bandwidth oscilloscope, triggered by the laser pulse, allowing for time-resolved decay analysis.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research demonstrates a critical need for high-quality, customized diamond substrates for advanced quantum and spintronics applications. 6CCVD is uniquely positioned to supply the necessary materials and fabrication services to replicate and extend this work.
Applicable Materials
Section titled “Applicable Materials”To replicate the high-sensitivity ODMR experiments and ensure optimal performance for CPW integration, the following 6CCVD material is required:
- Optical Grade Single Crystal Diamond (SCD): Required for its high purity, low strain, and excellent optical transparency (critical for 532 nm excitation and luminescence collection). 6CCVD supplies SCD optimized for post-growth processing (e.g., electron irradiation or ion implantation) necessary for creating high-coherence NV centers.
- Boron-Doped Diamond (BDD): For researchers extending the µ-PCD methodology to diamond, 6CCVD offers BDD films (PCD or SCD) with tunable conductivity, ideal for studying charge carrier dynamics and recombination in diamond itself.
Customization Potential
Section titled “Customization Potential”The success of the CPW structure relies on precise dimensions and potential metalization for low-loss contacts. 6CCVD offers comprehensive customization services:
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Custom Dimensions | Plates/wafers up to 125 mm (PCD) and custom SCD plates. | We can supply the exact 3 x 3 x 0.3 mm SCD dimensions used, or larger substrates up to 10 mm thick, ensuring compatibility with custom CPW designs. |
| Surface Preparation | Polishing to Ra < 1 nm (SCD) and Ra < 5 nm (PCD). | Ultra-smooth surfaces minimize optical scattering losses and ensure high-quality interface contact for CPW deposition. |
| CPW Contact Integration | In-house Custom Metalization services. | We offer deposition of standard CPW contact stacks (Au, Pt, Pd, Ti, W, Cu) directly onto the diamond substrate, streamlining the fabrication process for microwave engineers. |
| Thickness Control | SCD and PCD films from 0.1 µm up to 500 µm. | Precise control over substrate thickness is essential for optimizing microwave field confinement and coupling efficiency in the quasi-TEM mode of the CPW. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in the material science of diamond for quantum applications. We can assist researchers with:
- Material Selection: Determining the optimal nitrogen concentration and crystal orientation for maximizing NV center yield and coherence time in similar Quantum Sensing and Spintronics projects.
- Integration Consultation: Advising on the best practices for metalization and surface preparation to ensure robust, low-loss integration of CPW structures onto diamond substrates for broadband microwave delivery.
- Global Logistics: Offering global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Combined microwave-optical pump-probe methods are emerging to study the quantum state of spin qubit centers and the charge dynamics in semiconductors. A major hindrance is the limited bandwidth of microwave irradiation/detection circuitry which can be overcome with the use of broadband coplanar waveguides (CPWs). The development and performance characterization of two spectrometers is presented as follows: an optically detected magnetic resonance spectrometer (ODMR) and a microwave‐detected photoconductivity measurement. In the first method, light serves as detection and microwaves excite the investigated medium, whereas in the second, the roles are interchanged. The performance is demonstrated by measuring ODMR maps on the nitrogen‐vacancy (NV) center in diamond and time‐resolved photoconductivity in p ‐doped silicon. The results demonstrate both an efficient coupling of the microwave irradiation to the samples as well as an excellent sensitivity for minute changes in sample conductivity.