Hole injection contribution to transport mechanisms in metal/p−/p++ and metal/oxide/p−/p++ diamond structures
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2015-08-06 |
| Journal | physica status solidi (a) |
| Authors | Pierre Muret, David Eon, Aboulaye Traoré, Aurélien Maréchal, Julien Pernot |
| Institutions | Université Grenoble Alpes, Centre National de la Recherche Scientifique |
| Citations | 5 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Hole Injection in Diamond Heterostructures
Section titled “Technical Documentation & Analysis: Hole Injection in Diamond Heterostructures”This document analyzes the research paper “Hole injection contribution to transport mechanisms in metal/p-/p++ and metal/oxide/p-/p++ diamond structures” to highlight the critical material requirements and demonstrate how 6CCVD’s MPCVD diamond capabilities can support and advance this high-power electronics research.
Executive Summary
Section titled “Executive Summary”The analyzed research confirms the superior performance of vertical diamond power devices (Schottky diodes and MOS structures) utilizing a lightly doped (p-) layer stacked on a heavily boron-doped (p++) layer.
- Core Value Proposition: Efficient hole injection from the p++ layer into the p- layer significantly reduces specific resistance and forward losses, overcoming the limitation of incomplete boron acceptor ionization at room temperature.
- Performance Metrics: The optimized heterostructures achieved high current densities (> 1 kA/cm2) while maintaining exceptional reverse breakdown voltages (1.4 kV to 2 kV) and breakdown fields (> 7.7 MV/cm).
- Critical Design Parameter: Device operation is freed from temperature dependence and incomplete ionization limitations when the lightly doped p- layer thickness is sufficiently thin (typically < 2 µm).
- Specific Resistance Reduction: Hole injection resulted in a decrease of specific resistance by a factor larger than ten compared to predictions based on thermodynamic equilibrium concentration.
- Material Requirements: Success hinges on the precise control of doping concentration (from 5 x 1015 B/cm3 to 4 x 1020 B/cm3) and sub-micron layer thickness, capabilities central to 6CCVD’s MPCVD expertise.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the analysis of the fabricated diamond heterostructures:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Band Gap (EG) | 5.45 | eV | Intrinsic Property |
| Thermal Conductivity | 22 | W·cm-1·K-1 | Intrinsic Property |
| Breakdown Field (FBD) | > 7.7 | MV/cm | Demonstrated in p- layers |
| Reverse Breakdown Voltage | 1.4 to 2 | kV | Achieved in optimized p-/p++ stacks |
| Lightly Doped Layer (p-) Thickness | 1.3 | µm | Schottky Diode Structure |
| Lightly Doped Layer (p-) Concentration | 5 x 1015 | B/cm3 | Required for high voltage |
| Heavily Doped Layer (p++) Thickness | 0.2 | µm | Hole Injection Reservoir |
| Heavily Doped Layer (p++) Concentration | (2 - 4) x 1020 | B/cm3 | Exceeds metallic conductivity limit |
| Specific Resistance (Rs) | < 1 | Ω·cm2 | At room temperature (without injection effect) |
| Ideality Factor (n) | 1.07 (300 K) down to 1.04 (600 K) | N/A | Near-perfect Schottky junction |
| Homogeneous Barrier Height (ΦBhom) | 0.97 ± 0.02 | V | Zr/Oxidized Diamond Interface |
| Operating Current Density | > 1 | kA/cm2 | Forward bias operation |
Key Methodologies
Section titled “Key Methodologies”The experimental success relies on precise control over the epitaxial growth and subsequent device fabrication steps, particularly concerning doping and layer thickness.
- Epitaxial Growth: Diamond heterostructures (p-/p++ stacks) were grown epitaxially on Ib (HPHT) substrates, confirming the necessity of high-quality Single Crystal Diamond (SCD) material.
- Doping Profile Engineering:
- A heavily Boron-Doped (p++) layer (0.2 µm thick, 2-4 x 1020 B/cm3) was grown first to act as the hole injection reservoir.
- A lightly Boron-Doped (p-) layer (1.3 µm thick, 5 x 1015 B/cm3) was grown subsequently to bear the high reverse voltage.
- Schottky Diode Fabrication: Zirconium (Zr) metalization was applied to the oxidized diamond surface, followed by annealing at 450 °C to establish the Schottky contact.
- MOS Structure Fabrication: Aluminum (Al) was deposited on a 25 nm thick Al2O3 oxide layer, which was placed on a p-/p++ stack (p- layer 500 nm thick, 3 x 1017 B/cm3).
- Numerical Validation: Finite elements software (COMSOL Multiphysics) was used to simulate the valence band top and quasi-Fermi level profiles, confirming the transition from depletion to accumulation regime near the interface under forward bias.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate, optimize, and scale the vertical power devices described in this research. Our capabilities directly address the critical requirements for precise doping, thickness control, and custom metalization.
Applicable Materials
Section titled “Applicable Materials”To replicate or extend this research into high-power vertical devices, 6CCVD recommends the following materials:
- Single Crystal Diamond (SCD) Substrates: Required for high-quality homoepitaxial growth of the p-/p++ stack, ensuring the low defectivity necessary to achieve breakdown fields > 7.7 MV/cm.
- Heavy Boron Doped Diamond (BDD) Layers: Essential for the p++ injection layer. 6CCVD provides BDD layers with concentrations up to the metallic limit (approaching 1021 B/cm3), guaranteeing the temperature-independent hole reservoir required for efficient injection.
- Lightly Doped SCD Epitaxial Layers: We supply the lightly doped p- drift layers (5 x 1015 B/cm3 range) with the necessary low background impurity levels for high-voltage operation.
Customization Potential
Section titled “Customization Potential”| Requirement from Research Paper | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Precise Layer Thickness | SCD Thickness Control (0.1 µm - 500 µm) | We guarantee sub-micron precision for both the p++ injection layer (0.2 µm) and the p- drift layer (1.3 µm), enabling researchers to fine-tune the optimal thickness (< 2 µm) for minimal forward losses. |
| Custom Metalization Stacks | In-House Metalization (Au, Pt, Pd, Ti, W, Cu) | While Zr and Al were used in the study, 6CCVD offers custom metal stacks (e.g., Ti/Pt/Au) tailored for specific Schottky barrier heights or Ohmic contacts, streamlining device fabrication and testing. |
| Scaling for Commercialization | Custom Dimensions (Plates/wafers up to 125 mm PCD) | Our ability to supply large-area Polycrystalline Diamond (PCD) or large-area SCD substrates allows for the scaling of these high-performance vertical structures into commercial high-power modules. |
| Surface Quality | Polishing (Ra < 1 nm for SCD) | Ultra-smooth surfaces are critical for reliable interface formation (metal/diamond or oxide/diamond), minimizing interface inhomogeneities (σφ) and ensuring near-ideal ideality factors (n ≈ 1.07). |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in MPCVD growth recipes and material characterization. We can assist engineers and scientists with material selection, doping profile design, and thickness optimization for similar vertical power device projects, ensuring the material stack meets the stringent requirements for high breakdown voltage and low specific resistance demonstrated in this paper.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Heterostructures such as Schottky diodes and metal/oxide/ semiconductor structures are the building blocks of diamond electronic devices. They are able to carry large current densities, up to several kA cm , if a heavily boron‐doped layer (p ) is included in the semiconducting stack, thus affording a metallic reservoir of mobile holes close to the lightly doped layer (p ). In this work, hole injection effects are evidenced experimentally in the two previously mentioned devices and also simulated numerically. Although the potential barrier height at metal/semiconductor interfaces is a fundamental parameter, a more general approach consists in defining the current density from the product of an effective velocity and carrier concentration at interface. In accordance with experimental results, such a view permits to describe both depletion and accumulation regimes, which indeed can exist at the metallic or oxide interface, and to take into account the increase of the hole concentration above the thermal equilibrium one in the p layer. The lower the temperature, the larger is this second effect. For sufficiently thin p layers, typically below 2 m, this effect frees device operation from the limitation due to incomplete ionization of acceptors and allows a strong decrease of the specific resistance and forward losses while preserving breakdown voltages in the range of 1.4-2 kV.