Diamond Schottky diodes operating at 473 K

At a Glance

Metadata	Details
Publication Date	2017-07-03
Journal	EPE Journal
Authors	Richard Monflier, Karine Isoird, Alain Cazarré, Josiane Tasselli, Alexandra Servel
Institutions	Laboratoire d’Analyse et d’Architecture des Systèmes, Centre National de la Recherche Scientifique
Citations	2
Analysis	Full AI Review Included

6CCVD Technical Documentation: High-Temperature Diamond Schottky Diodes

Reference Publication: Diamond Schottky diodes operating at 473 K (Monflier et al.) Subject Area: High-Power, High-Temperature Wide Band Gap Electronics

Executive Summary

This paper successfully demonstrates the reliable operation of p-type Boron-Doped (BDD) MPCVD diamond Schottky diodes at elevated temperatures (up to 473 K / 200 °C). These results confirm diamond’s superior potential for extreme environment power electronics compared to SiC or GaN.

High-Temperature Functionality: Vertical and pseudo-vertical diamond Schottky diodes exhibited robust operation up to 473 K (200 °C).
Performance Metrics: Achieved current densities exceeding 1000 A/cm² at 473 K for pseudo-vertical structures.
Reproducibility: Demonstrated high functionality rates: 75% (Vertical Diodes) and 97% to 100% (Pseudo-Vertical Diodes) across tested batches.
Leakage Control: Maintained ultra-low reverse leakage current (< 10⁻⁷ A/cm²) up to 50 V reverse bias, predicting high breakdown capability.
Material Optimization Needed: Performance is currently limited by the high series resistance of the P⁻ drift layer and inadequate doping concentration in the P⁺ contact layer (targeting 10¹⁹ cm⁻³), highlighting the need for highly controlled, thick BDD layer growth.
Processing Validation: Successful integration of standard metal stacks (Ti/Pt/Au ohmic, Ni/Au Schottky) stable under elevated temperature operation.

Technical Specifications

Key performance data and physical parameters extracted from the vertical and pseudo-vertical diamond Schottky diodes.

Parameter	Value (Vertical Diode)	Value (Pseudo-Vertical Diode, 100 µm)	Unit	Context
Operating Temperature (T)	473 (200 °C)	473 (200 °C)	K	Stable, High Functionality
Max Forward Current Density	488	> 1000	A/cm²	At 473 K, 10 V bias
Reverse Leakage Current Density	< 10⁻⁷	< 10⁻⁷	A/cm²	At 50 V reverse bias
Measured Breakdown Voltage (BV)	N/A	190	V	Pseudo-Vertical Diode (100 µm)
Simulated Breakdown Voltage (BV)	1600	510	V	2D Simulated Schottky Diode
Series Resistance (R_S)	193	N/A	Ω	At 473 K, significant reduction from 296 K (934 Ω)
Schottky Barrier Height (Φ_B)	1.38	2.09	eV	Measured at 473 K
Non-Ideality Factor (n)	1.77	1.24	N/A	Lower factor attributed to dominant thermionic emission

Material & Structure Parameters

Layer	Doping Concentration ([B])	Thickness	Unit	Context
P⁺ Layer (Substrate/Contact)	1.10¹⁹ - 5.10¹⁹	480	µm	Vertical Diode structure
P⁻ Layer (Drift)	1.10¹⁵ - 5.10¹⁵	8	µm	Vertical Diode structure
Pseudo-Vertical P⁻ Layer	1.4.10¹⁶	10	µm	Determined by C(V) measurements

Key Methodologies

The devices utilized p-type Boron-Doped CVD diamond grown via MPCVD. The fabrication process focuses on achieving stable ohmic and Schottky contacts suitable for high-temperature operation.

1. Material Growth and Structure

Base Material: P-type Boron-Doped CVD diamond films (SCD implied for vertical structure control).
Structure: Two primary geometries were tested:
- Vertical Diodes: P⁻ layer (8 µm) grown on a heavily doped P⁺ substrate (480 µm).
- Pseudo-Vertical Diodes: P⁻ layer (10 µm) grown on a P⁺ layer (22 µm) on a non-conductive substrate.
Dopant: Boron (p-type). High activation energy (0.37 eV) necessitates elevated temperatures (473 K) for optimal carrier activation.

2. Metallization and Contact Formation

Ohmic Contacts (P⁺ Layer):
- Stack: Ti (50 nm) / Pt (50 nm) / Au (500 nm).
- Annealing: Performed at 723 K (450 °C) for 30 minutes to ensure stable, low-resistance contact.
- Note: The authors emphasize the need to optimize ohmic contact processes to reduce electrical contact resistivity on the P⁺ layer (doped around 10¹⁹ cm⁻³).
Schottky Contacts (P⁻ Layer):
- Stack: Ni (50 nm) / Au (450 nm).
- Note: The paper suggests a new surface treatment and annealing step could be beneficial to improve the metal/diamond interface quality and adhesion stability.

3. High-Temperature Electrical Testing

Measurements: Current-Voltage (I-V) characteristics were recorded across a temperature range (296 K to 473 K).
Reverse Bias: Leakage current density measurements were conducted up to 50 V.
C(V) Analysis: Capacitance-Voltage measurements (at 5 MHz) were used to extract the doping concentration of the unintentionally doped P⁻ layer.
Breakdown Testing: Performed under vacuum at room temperature.

6CCVD Solutions & Capabilities

The challenges highlighted in this research—optimizing heavy boron doping, achieving ultra-low layer resistance, ensuring precise layer thickness control, and stable high-temperature metal contacts—are directly addressed by 6CCVD’s specialized MPCVD capabilities.

Applicable Materials

To replicate or advance the high-power density diamond diodes demonstrated in this work, 6CCVD offers the following optimized materials:

6CCVD Material Solution	Specification Match	Technical Advantage for Replication
Heavy Boron-Doped SCD (BDD)	P⁺ Layer (10¹⁹ cm⁻³)	Optimized recipes for high-concentration, uniform Boron doping, directly resolving the low P⁺ doping/high resistance limitation cited in the paper.
Unintentionally Doped SCD	P⁻ Drift Layer (10¹⁵ cm⁻³)	High-purity single crystal diamond (SCD) for stable drift layers, maximizing thermal conductivity (20 W·cm⁻¹·K⁻¹) and breakdown field (10 MV·cm⁻¹).
SCD Substrates (Thick)	Vertical Device Substrate	Custom substrate thicknesses up to 10 mm, suitable for vertical device architectures requiring thick, highly conductive base layers (480 µm P⁺ layer requirement is easily met).

Customization Potential

6CCVD provides the necessary engineering control and post-processing capabilities essential for producing reliable diamond power devices:

Precision Layer Control: The vertical diode architecture requires a thin P⁻ drift layer (8 µm) on a thick P⁺ substrate (480 µm). 6CCVD guarantees thickness uniformity and control for SCD layers from 0.1 µm up to 500 µm, crucial for precise resistance and breakdown voltage tuning.
Advanced Surface Preparation: The paper notes limitations due to interface quality (high charge density at the Schottky contact). 6CCVD offers Ra < 1 nm polishing for SCD wafers to minimize surface defects, providing an ideal template for subsequent metal deposition and improving the barrier height uniformity.
Custom Metalization Stacks: The Ti/Pt/Au and Ni/Au stacks used are standard capability. 6CCVD provides in-house e-beam and sputter deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to rapidly iterate on contact metallurgy to improve adhesion and stability at high operating temperatures (up to 723 K processing).
Custom Dimensions and Patterning: Diode fabrication (100 µm diameter/square elements) requires precise patterning. 6CCVD supports custom laser cutting and shaping of diamond wafers (up to 125 mm diameter) for specific device geometries.

Engineering Support

Diamond electronics presents complex fabrication challenges, particularly concerning doping control and interfacial stability. 6CCVD’s in-house PhD team specializes in CVD growth kinetics and material characterization.

Our experts can assist researchers in optimizing the Boron doping profiles needed to achieve the low series resistance required for high-current density power devices.
We offer consultation on material selection (SCD vs. PCD) and surface pre-treatment protocols necessary to improve metal adhesion and reduce interface traps for high-temperature Schottky diodes and similar Wide Band Gap Power Conversion projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1080/09398368.2017.1388625