Peculiarities of high electric field conduction in p-type diamond

At a Glance

Metadata	Details
Publication Date	2016-04-11
Journal	Applied Physics Letters
Authors	V. Mortet, David Trémouilles, J. Bulı́ř, Pavel Hubı́k, Luděk Heller
Institutions	Laboratoire d’Analyse et d’Architecture des Systèmes, Centre National de la Recherche Scientifique
Citations	7
Analysis	Full AI Review Included

Technical Analysis and Commercial Solutions for High Electric Field Conduction in p-Type Diamond

Reference: Peculiarities of high electric field conduction in p-type diamond (Mortet et al.) Subject: Investigation of electrical properties and reversible impurity impact ionization avalanche breakdown in Boron-Doped CVD diamond using Transmission-Line Pulse (TLP) method.

Executive Summary

This research validates the critical potential of Boron-Doped Diamond (BDD) epitaxial layers for next-generation high-power electronic devices, specifically demonstrating stable, reversible avalanche breakdown through impurity impact ionization.

Core Achievement: Observation of the S-shape current-voltage (I-V) characteristic, signifying differential negative resistance and complete ionization of neutral boron impurities in p-type diamond.
Mechanism Verified: The breakdown is confirmed to be a diamond-bulk electrical phenomenon (impurity impact ionization) rather than thermal self-heating or air arcing, by utilizing high-speed (100 ns) TLP measurements.
Performance Metrics: Critical electric breakdown fields were consistently observed between 128 and 214 kV.cm^-1, depending on acceptor concentration.
Material Necessity: Successful replication relies fundamentally on high-quality, ultra-smooth (< 1 nm R_RMS) SCD substrates for low-defect epitaxial growth and precise control over boron acceptor concentration.
Engineering Implication: The documented high current density (up to 2 MA.cm^-2) and high power dissipation (~100 W post-breakdown) confirm BDD’s robust potential for use in switches, limiters, and high-frequency power devices operating above the typical diamond freeze-out temperature range.
6CCVD Advantage: 6CCVD provides the necessary high-purity Single Crystal Diamond (SCD) substrates and highly controlled Boron-Doped Diamond (BDD) epitaxial growth required to replicate and scale these high-field devices.

Technical Specifications

The following table summarizes the critical material, processing, and performance parameters extracted from the study, demonstrating the requirements for engineering these high-field BDD devices.

Parameter	Value	Unit	Context
Epitaxial Layer Thickness	2	µm	Boron-doped p-type layer
Substrate Orientation & Material	(100)	N/A	Synthetic HPHT Ib SCD (Sumicrystal UP)
Surface Roughness (R_RMS)	< 1	nm	Required for both substrate and epitaxial layer
TLP Pulse Width	100	ns	Used for quasi-static I-V characterization
TLP Rise/Fall Time	1	ns	Ensures minimal thermal effects
Critical Electric Field (Min)	128	kV.cm^-1	Heaviest doping (Sample 1: 3 x 10¹⁹ cm^-3)
Critical Electric Field (Max)	214	kV.cm^-1	Lightest doping (Sample 3: 1 x 10¹⁹ cm^-3)
Acceptor Concentration Range ([B])	1 x 10¹⁹ to 3 x 10¹⁹	cm^-3	Studied doping range
Carrier Mobility (Max)	286	cm².V^-1.s^-1	Lightest doping (Sample 3)
Activation Energy (E_A) Range	210 - 265	meV	Dependent on doping level
Ohmic Contact Structure	Ti/Au	N/A	Evaporated and annealed at 450 °C
Electrode Gap (d) Range	4 to 40	µm	Device geometry tested
Maximum Post-Breakdown Current Density	~ 2	MA.cm^-2	Measured in highly conductive region 5
Critical Voltage Temp. Dependence (V_c)	V_c ~ T^-1.3	N/A	Consistent with classic impurity impact ionization

Key Methodologies

The robust determination of high electric field conduction relied on a tightly controlled fabrication and measurement sequence focused on eliminating parasitic effects, such as thermal self-heating and air breakdown.

Substrate Preparation:
- Synthetic Ib (100) SCD substrates were re-polished using scaife techniques to achieve sub-surface damage removal and an ultra-smooth finish (R_RMS < 1 nm).
- Substrates were extensively cleaned: hot sulphuric acid/potassium nitrate oxidizing mixture, followed by ultrasonic cleaning in acetone and isopropyl alcohol.
- In-situ plasma cleaning: Substrates were etched in H₂/O₂ plasma for 10 min prior to growth.
MPCVD Epitaxial Growth:
- MW PECVD using a Seki Diamond Systems AX5010 reactor.
- Parameters: 1% CH₄ in H₂ mixture, 100 mbar pressure, 550 W microwave power.
- Doping: Trimethylboron precursor used to achieve acceptor concentrations between 1 x 10¹⁹ and 3 x 10¹⁹ cm^-3.
- Temperature: High substrate temperature maintained between 1000 °C and 1100 °C.
Device Fabrication:
- Device patterning via Reactive Ion Etching (RIE) using an Al mask defined by mask-less photolithography. Etch chemistry was Ar, O₂, CF₄, and He mixture (10:40:1:1 in volume).
- Ohmic contacts (Ti/Au) were deposited via evaporation (Edwards Auto 500 Vacuum System).
- Contacts were annealed at 450 °C for 30 min in vacuum to ensure low resistance ohmic performance.
TLP Electrical Characterization:
- Quasi-static I-V characteristics measured using the Transmission-Line Pulsing (TLP) technique (100 ns pulses, 1 ns edges) to suppress thermal effects.
- A 510 Ω surface mount resistance was placed in series with the tested samples (inter-electrode gaps 4 to 40 µm) to limit the current post-breakdown.
- Measurements utilized a 6 GHz bandwidth oscilloscope for accurate time-domain analysis of voltage and current pulses.

6CCVD Solutions & Capabilities

This study confirms diamond’s suitability for extreme power and high-field applications, which demands the highest grade of material engineering. 6CCVD is uniquely positioned to supply the materials and processing required to replicate and advance this research into commercial prototypes.

Applicable Materials

To replicate the reversible impact ionization avalanche breakdown demonstrated, researchers require highly controlled, high-quality p-type epitaxial diamond.

6CCVD Material Recommendation	Specification Match	Commercial Advantage
Heavy Boron-Doped (BDD) SCD Epitaxial Layers	Required B acceptor concentration (10¹⁹ cm^-3 range) for high-field conduction.	Precise, repeatable doping control in the bulk layer thickness (up to 500 µm capability).
Optical/Electronic Grade (100) SCD Substrates	Low-defect, re-polished substrates essential for R_RMS < 1 nm epitaxial interfaces.	Standard substrates available up to 125 mm diagonal; superior in-house polishing (Ra < 1 nm SCD).
High Purity Polycrystalline (PCD) Wafers	Suitable for large-area power devices where SCD cost is prohibitive.	6CCVD PCD available up to 125 mm diameter with superior polishing (Ra < 5 nm inch-size PCD).

Customization Potential

The experimental setup relied on highly precise device geometries and specific metal contacts. 6CCVD offers complete customization services to meet these exacting specifications:

Dimensional Control: The devices used inter-electrode gaps from 4 to 40 µm. 6CCVD provides custom laser cutting and shaping of wafers up to 125 mm, allowing researchers to design and test specific device geometries (e.g., custom micro-bar structures, variable electrode distances).
Precision Polishing: The material used required R_RMS < 1 nm to minimize surface scattering effects. 6CCVD guarantees electronic grade polishing (Ra < 1 nm for SCD) across production-scale wafers, ensuring reproducible electrical performance.
Advanced Metalization: The study utilized Ti/Au ohmic contacts, which is a core capability of 6CCVD. We offer deposition of a comprehensive range of metals—including Au, Pt, Pd, Ti, W, and Cu—in single or multi-layer stacks, tailored for specific ohmic or Schottky requirements.

Engineering Support

The relationship between breakdown field, acceptor concentration, and temperature is complex, requiring deep material expertise.

6CCVD’s in-house PhD engineering team specializes in modeling and manufacturing CVD diamond materials for extreme environments. We offer consultation services specifically focused on optimizing Boron concentration profiles and selecting the appropriate substrate (SCD vs. PCD) for high-field switching and surge protection projects.
We can assist in integrating custom metalization schemes and packaging solutions (crucial for dissipating the 100 W power levels observed post-breakdown) into TLP-tested devices.

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

View Original Abstract

The electrical properties of chemical vapour deposited p-type epitaxial diamond layers are studied in high electric field conditions. The quasi-static current-voltage characteristics have been measured using transmission-line pulse method with 100 ns pulses. Reproducible impurity impact ionization avalanche breakdown occurs at a critical electrical field in the range of 100-200 kV cm−1 depending on the acceptor concentration and temperature, leading to complete ionisation of neutral impurities. The current-voltage characteristics exhibit an S-shape with the bi-stable conduction characteristic of impurity impact ionisation.