Optical and electronic properties of sub-surface conducting layers in diamond created by MeV B-implantation at elevated temperatures

At a Glance

Metadata	Details
Publication Date	2016-06-13
Journal	Journal of Applied Physics
Authors	L. H. Willems van Beveren, Rong Liu, H.C. Bowers, Kumaravelu Ganesan, Brett C. Johnson
Institutions	Western Sydney University, The University of Melbourne
Citations	14
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Fluence Boron Implantation in Diamond

Executive Summary

This research successfully demonstrates the creation of highly conductive, sub-surface boron-doped layers in single-crystal diamond (SCD) using high-energy ion implantation combined with dynamic and high-temperature annealing. This methodology is critical for advanced diamond electronics and quantum applications requiring precise, deep doping profiles.

High Doping Achieved: Peak Boron concentration reached 1 x 10²² B cm^-3 (6 at.%), significantly exceeding typical solubility limits in CVD growth.
Graphitization Prevention: Dynamic annealing during 2 MeV B-implantation at 600°C successfully inhibited graphitization, preserving the diamond lattice integrity.
Lattice Recovery: Post-implantation High Temperature Annealing (HTA) at 1300°C removed remaining point defects, confirmed by Raman spectroscopy.
High Activation: Room Temperature (RT) Hall measurements showed carrier densities up to 3.37 x 10²¹ cm^-3, indicating a high activation fraction (33.7% for Plate B), well above the Metal-Insulator-Transition (MIT) critical limit.
Precise Profile Control: The buried conductive layer was tightly controlled, measuring approximately 100 nm thick at a depth of 1.37 µm, with negligible boron diffusion during HTA.
Device Integration: Robust, low-resistance electrical contacts were achieved using laser milling and back brazing, enabling precise van der Pauw characterization.

Technical Specifications

The following hard data points were extracted from the experimental results and simulations (Table I and text):

Parameter	Value	Unit	Context
Implantation Energy	2	MeV	Boron ions
Implantation Temperature	600	°C	Dynamic annealing
Post-Implant Annealing (HTA)	1300	°C	Vacuum, 10-15 minutes
Plate B Fluence (Dose)	1 x 10¹⁷	B cm^-2	Highest concentration sample
Projected Range (R_p)	1.37	µm	Depth of buried layer
Sheet Thickness (t_s)	~100	nm	Full Width Half Maximum (FWHM)
Peak B Concentration (Plate B)	1 x 10²²	B cm^-3	Equivalent to 6 at.%
RT Resistivity (Plate B, $\rho$_xx)	0.47 x 10^-3	Ω-cm	Sub-surface layer
RT Carrier Density (Plate B, n_3D)	3.37 ± 0.5 x 10²¹	cm^-3	Exceeds MIT critical density
RT Mobility (Plate B, $\mu$)	3.89 ± 0.5	cm²V^-1s^-1	Room temperature
Low T Mobility (Plate B, 4K, $\mu$)	57.9 ± 3.7	cm²V^-1s^-1	Significant increase at low temperature
Activation Energy (Plate B)	1.5 ± 0.1	meV	Extracted from Arrhenius plot (100K to RT)

Key Methodologies

The fabrication and characterization process relied on precise control over implantation conditions and post-processing steps to manage lattice damage and dopant activation.

Material Preparation: Type IIa (100) single-crystal diamond plates were used as the starting material.
Hot Ion Implantation: 2 MeV Boron ions were implanted at an elevated temperature (600°C) to promote in-situ dynamic annealing, preventing the formation of irreversible graphitic phases.
Surface Cleaning: Post-implantation, plates were subjected to Bristol acid boiling to remove any residual surface graphitization.
High Temperature Annealing (HTA): Samples were annealed in vacuum at 1300°C for 10-15 minutes to activate the substitutional boron ions and recover the diamond lattice structure from implantation damage.
Device Patterning: A van der Pauw square configuration was patterned onto the plates, requiring four electrodes with a 500 µm contact spacing.
Contact Fabrication: Robust, low-resistance electrical contacts to the buried sub-surface layer were achieved using a specialized laser milling and back brazing process.
Characterization:
- Structural: Raman and Photoluminescence (PL) spectroscopy (532 nm excitation) were used to quantify lattice damage and defect removal (e.g., NV centers, split-interstitials).
- Doping Profile: Dynamic Secondary Ion Mass Spectrometry (SIMS) was used to map the B concentration profile and confirm the projected range (R_p) and sheet thickness (t_s).
- Electronic: Low-temperature Hall and magnetoresistance measurements (down to 4 K and 120 mK) were performed using a cryogen-free dilution refrigerator to extract carrier density, mobility, and resistivity.

6CCVD Solutions & Capabilities

This research highlights the critical need for ultra-high-quality diamond substrates to minimize compensating defects (like nitrogen) and maximize carrier mobility in heavily doped structures. 6CCVD is uniquely positioned to supply the foundational materials and custom processing required to replicate and advance this work, particularly in the pursuit of diamond-based superconductivity and high-power electronics.

Applicable Materials for Replication and Extension

The paper concludes that reducing nitrogen content (from ppm to ppb) would significantly reduce compensation doping and scattering. 6CCVD offers the ideal solution:

6CCVD Material	Description	Application Relevance
Electronic Grade SCD	Ultra-low nitrogen content (< 5 ppb). High crystalline purity, Type IIa.	Directly addresses the paper’s conclusion. Essential for minimizing compensation effects and maximizing carrier mobility in high-fluence implantation studies.
Optical Grade SCD	High purity, suitable for general MeV implantation studies where optical transparency is required.	Excellent starting material for high-energy implantation and subsequent optical characterization (Raman/PL).
Boron-Doped Diamond (BDD)	SCD or PCD doped in-situ during growth (up to 10²¹ cm^-3).	Ideal for comparative studies against implantation methods, or for creating multi-layer structures (e.g., highly conductive BDD seed layers).

Customization Potential for Device Fabrication

The fabrication process described requires precise material dimensions, deep etching (laser milling), and specialized metal contacts—all core capabilities of 6CCVD.

Custom Dimensions and Substrates: 6CCVD provides Single Crystal Diamond (SCD) plates in custom dimensions and orientations (e.g., (100) used in the study). We offer thicknesses from 0.1 µm up to 500 µm, and substrates up to 10 mm thick, ensuring compatibility with high-energy MeV implantation equipment.
Advanced Polishing: To ensure uniform implantation and high-quality surface analysis (SIMS, Raman), 6CCVD guarantees SCD polishing with Ra < 1 nm.
Integrated Metalization Services: The paper required robust, low-resistance contacts via brazing. 6CCVD offers in-house custom metalization stacks (e.g., Ti/Pt/Au, Ti/W/Cu) tailored for specific contact requirements, including ohmic contacts to heavily p-type doped layers, eliminating the need for external brazing processes.
Precision Patterning: We offer laser cutting and micro-machining services to define precise device geometries, such as the van der Pauw squares or Hall bar structures, necessary for accurate electronic transport measurements.

Engineering Support

6CCVD’s in-house PhD material science team specializes in the growth and characterization of doped and high-purity diamond. We can assist researchers and engineers with material selection for similar High-Fluence Ion Implantation projects, ensuring the optimal substrate purity and orientation are chosen to achieve desired carrier activation and mobility targets.

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

View Original Abstract

Boron implantation with in-situ dynamic annealing is used to produce highly conductive sub-surface layers in type IIa (100) diamond plates for the search of a superconducting phase transition. Here, we demonstrate that high-fluence MeV ion-implantation, at elevated temperatures avoids graphitization and can be used to achieve doping densities of 6 at. %. In order to quantify the diamond crystal damage associated with implantation Raman spectroscopy was performed, demonstrating high temperature annealing recovers the lattice. Additionally, low-temperature electronic transport measurements show evidence of charge carrier densities close to the metal-insulator-transition. After electronic characterization, secondary ion mass spectrometry was performed to map out the ion profile of the implanted plates. The analysis shows close agreement with the simulated ion-profile assuming scaling factors that take into account an average change in diamond density due to device fabrication. Finally, the data show that boron diffusion is negligible during the high temperature annealing process.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4953583

References

2008 - Constraints on Tc for superconductivity in heavily boron-doped diamond [Crossref]
2004 - Superconductivity in diamond [Crossref]
2004 - Dependence of the superconducting transition temperature on the doping level in single-crystalline diamond films [Crossref]
2004 - Superconductivity in diamond thin films well above liquid helium temperature [Crossref]
2007 - Superconducting properties of homoepitaxial CVD diamond [Crossref]
2009 - Superconductivity in CVD diamond films [Crossref]
2010 - Critical concentrations of superconductor to insulator transition in (111) and (001) CVD boron-doped diamond [Crossref]
2006 - Superconductivity and low temperature electrical transport in B-doped CVD nanocrystalline diamond [Crossref]
2015 - Signature of high Tc around 25 K in high quality superconducting diamond [Crossref]
2008 - Absence of superconductivity in boron-implanted diamond [Crossref]