Optical Pump–Terahertz Probe Diagnostics of the Carrier Dynamics in Diamonds

At a Glance

Metadata	Details
Publication Date	2023-12-26
Journal	Materials
Authors	V. V. Bulgakova, P. A. Chizhov, A. А. Ushakov, P. V. Ratnikov, Yuri Goncharov
Institutions	MIREA - Russian Technological University, Moscow Institute of Physics and Technology
Citations	2
Analysis	Full AI Review Included

Optical Pump-Terahertz Probe Diagnostics of Carrier Dynamics in Diamonds: 6CCVD Technical Analysis

This document analyzes the research on photoinduced carrier dynamics in diamond composites for ultrafast Terahertz (THz) applications, providing technical specifications and outlining how 6CCVD’s advanced MPCVD diamond capabilities can support and extend this critical research area.

Executive Summary

Application Focus: The study validates diamond and novel diamond-silicon composites as high-performance substrates for Large-Aperture Photoconductive Antennas (LAPCAs) and ultrafast flexible THz wave modulation.
Novel Material Achievement: A two-step Microwave Plasma Chemical Vapor Deposition (MPCVD) process successfully created a Polycrystalline Diamond (PCD) composite embedding 100 nm-2 µm silicon microparticles.
Ultrafast Dynamics: The Si-diamond composite exhibited dual photocarrier relaxation dynamics, featuring an exceptionally fast component (t_sifast = 4 ± 0.5 ps).
Performance Comparison: This fast relaxation time is several times shorter than those observed in traditional High-Pressure High-Temperature (HPHT) Boron-doped (17-55 ps) or Nitrogen-doped (10-25 ps) diamond samples.
Mechanism: The ultrafast dynamics are attributed to efficient charge carrier transport and separation occurring at the silicon-diamond interface, delaying recombination.
6CCVD Value Proposition: 6CCVD specializes in custom MPCVD growth, defect engineering (BDD, N-doping), and composite fabrication necessary to optimize these ultrafast diamond materials for next-generation THz devices.

Technical Specifications

The following hard data points were extracted from the experimental results concerning carrier dynamics and material properties:

Parameter	Value	Unit	Context
Fast Carrier Lifetime (t_sifast)	4 ± 0.5	ps	Si-diamond composite (Ultrafast component)
Slow Carrier Lifetime (t_sislow)	220 ± 100	ps	Si-diamond composite (Delayed recombination)
N-Doped Lifetime (t_100ppm)	10 ± 1	ps	HPHT Diamond (100 ppm N)
B-Doped Lifetime (t_1ppm)	17 ± 1	ps	HPHT Diamond (1 ppm B)
THz Probing Range	0.3 - 3	THz	Corresponding to 1.2 meV to 12.4 meV photon energy
Pump Excitation Wavelength	800 / 400	nm	Fundamental / Second Harmonic
Optical Fluence Range Tested	60 to 170	µJ/cm²	Linear dependence observed in this range
PCD Film Total Thickness	19	µm	CVD Polycrystalline Diamond
Si Particle Size Range	100 nm - 2	µm	Embedded in PCD matrix

Key Methodologies

The Si-diamond composite was fabricated using a specialized two-step MPCVD process to achieve precise material layering and particle encapsulation.

Substrate Preparation: Silicon <100> substrate (10 × 10 mm) was seeded using nanodiamond particles (3-7 nm) with a zeta potential >+50 mV to establish nucleation centers.
First PCD Layer Growth: A 15 µm thick Polycrystalline Diamond (PCD) layer was grown via MPCVD (2.45 GHz, 4.5 kW power).
Intermediate Layer Application: Milled silicon microparticles (100 nm-2 µm) suspended in Dimethylsulfoxide (DMSO) were spin-coated onto the PCD surface (3000 rpm).
Second PCD Layer Growth: A 4 µm thick PCD layer was grown via MPCVD to completely encapsulate the Si microparticles within the diamond matrix, resulting in a total film thickness of 19 µm.
CVD Growth Parameters: The process utilized a fixed total gas flow of 500 sccm, a high Methane (CH₄) content of 4% in Hydrogen (H₂), 75 Torr pressure, and a substrate temperature of 840 °C.
Membrane Formation: The silicon substrate was partially removed via chemical etching (HF:HNO₃, 3:1 mixture at 40 °C) to isolate the diamond membrane.
OPTP Measurement: Carrier dynamics were measured using an Optical Pump-Terahertz Probe setup employing a Ti:Sapphire laser (800 nm, 40-150 fs pulse duration, 1 kHz repetition rate).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the custom diamond materials and engineering services required to replicate, optimize, and scale the high-performance THz modulation platform demonstrated in this research.

Research Requirement	6CCVD Applicable Materials & Services	Technical Relevance & Sales Advantage
Composite Material Synthesis	Custom PCD & Substrate Integration: 6CCVD offers specialized MPCVD growth recipes for embedding foreign materials (e.g., Si micro/nanoparticles, metals) within PCD or SCD matrices.	Enables the development of novel diamond-based heterostructures and composites for tailored charge transport dynamics and ultrafast switching.
Polycrystalline Diamond (PCD) Substrates	Large-Area PCD Wafers: We supply high-quality PCD plates up to 125 mm in diameter, suitable for scaling LAPCA fabrication.	Provides the necessary large-aperture, high-breakdown-threshold substrates required for high-power THz generation.
Thin Film and Membrane Fabrication	Precision Thickness Control: PCD and SCD films available from 0.1 µm to 500 µm. We manage the full process, including controlled substrate removal, to yield robust diamond membranes.	Critical for applications requiring minimal material volume, such as MEMS, pressure sensors, or optimized THz transmission windows.
Carrier Lifetime Engineering	Boron-Doped Diamond (BDD): 6CCVD offers highly controlled Boron-Doped Diamond (BDD) via MPCVD, allowing precise tuning of defect density and carrier lifetime, essential for optimizing THz modulator speed and efficiency.	Achieve specific, repeatable relaxation times (e.g., 10 ps to 100s of ps) by controlling the concentration of dopants and defects, surpassing the limitations of HPHT materials.
Surface Quality and Integration	Advanced Polishing and Metalization: Polishing services achieve Ra < 5 nm for inch-size PCD. We offer in-house metalization (Au, Pt, Ti, W, Cu) for electrode integration.	Ensures low optical scattering losses for OPTP experiments and provides necessary electrical contacts for functional LAPCA devices.
Global Supply Chain	Global Shipping (DDU/DDP): We provide reliable, insured global shipping options to ensure timely delivery of sensitive materials to research facilities worldwide.	Facilitates seamless material acquisition for international research collaborations.

6CCVD’s in-house PhD team can assist with material selection and custom growth parameter development for similar ultrafast THz modulation and photoconductive antenna projects.

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

View Original Abstract

Diamond is a promising material for terahertz applications. In this work, we use a non-invasive optical pump-terahertz probe method to experimentally study the photoinduced carrier dynamics in doped diamond monocrystals and a new diamond-silicon composite. The chemical vapor deposited diamond substrate with embedded silicon microparticles showed two photoinduced carrier lifetimes (short lifetime on the order of 4 ps and long lifetime on the order of 200 ps). The short lifetime is several times less than in boron-doped diamonds and nitrogen-doped diamonds which were grown using a high temperature-high pressure technique. The observed phenomenon is explained by the transport of photoexcited carriers across the silicon-diamond interface, resulting in dual relaxation dynamics. The observed phenomenon could be used for ultrafast flexible terahertz modulation.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17010119

References

2020 - Real-time terahertz imaging with a single-pixel detector [Crossref]
2021 - Functional THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces [Crossref]
2021 - High-power portable terahertz laser systems [Crossref]
2019 - Broadband THz to NIR up-converter for photon-type THz imaging [Crossref]
2016 - Intense THz pulses with large ponderomotive potential generated from large aperture photoconductive antennas [Crossref]
2021 - Intense terahertz generation from photoconductive antennas [Crossref]
2020 - An overview of terahertz antennas [Crossref]