GaN-based lateral diode with nanocrystalline diamond passivation layer
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-01-01 |
| Journal | Acta Physica Sinica |
| Authors | Zeyang Ren, SONG Songyuan, Tao Zhang, CHEN Heyuan, Yao Li |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Nanocrystalline Diamond Passivation for GaN SBDs
Section titled âTechnical Documentation & Analysis: Nanocrystalline Diamond Passivation for GaN SBDsâ6CCVD Material Science Analysis of âGaN-based lateral diode with nanocrystalline diamond passivation layerâ
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the use of Nanocrystalline Diamond (NCD) grown via Microwave Plasma Chemical Vapor Deposition (MPCVD) as a superior passivation and thermal management layer for GaN Schottky Barrier Diodes (SBDs).
- Core Value Proposition: NCD passivation drastically improves the thermal stability and suppresses current collapse in high-power GaN devices, addressing a critical bottleneck in power electronics.
- Thermal Performance: NCD-passivated SBDs (Device A) achieved thermal failure resistance up to 7.5 W/mm, significantly exceeding the 4 W/mm limit of conventional SiN-passivated devices (Device B).
- Thermal Resistance Reduction: The NCD layer reduced the effective thermal resistance (Rth) from 8.73 K·mm·W-1 (SiN) to 7.37 K·mm·W-1, confirming enhanced heat spreading near the junction.
- Current Collapse Suppression: Dynamic pulse testing showed NCD devices maintained excellent electrical stability, exhibiting only 2.6% current density degradation (compared to 99.9% degradation for SiN devices).
- Material Specification: The NCD film was grown to a thickness of 380-450 nm with a controlled grain size of 330-380 nm using a low-temperature MPCVD process (650 °C).
- Application Potential: This work is the first reported application of NCD passivation for thermal management in GaN power diodes, validating the strategy for non-HEMT power device architectures.
Technical Specifications
Section titled âTechnical SpecificationsâHard data extracted from the research paper comparing NCD (Device A) and SiN (Device B) performance.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NCD Film Thickness | 380-450 | nm | Measured via SEM cross-section |
| NCD Grain Size | 330-380 | nm | Measured via SEM surface morphology |
| NCD Growth Temperature | 650 | °C | Low-temperature MPCVD process |
| NCD Thermal Resistance (Rth) | 7.37 | K·mm·W-1 | Device A (NCD) |
| SiN Thermal Resistance (Rth) | 8.73 | K·mm·W-1 | Device B (SiN) |
| Max Output Power Density (NCD) | 7.5 | W/mm | Before thermal failure (Device A) |
| Max Output Power Density (SiN) | 4 | W/mm | Before thermal failure (Device B) |
| Current Collapse Degradation (NCD) | 2.6 | % | At -20 V DC bias, 2.5 V pulse |
| Current Collapse Degradation (SiN) | 99.9 | % | At -20 V DC bias, 2.5 V pulse |
| Forward Turn-On Voltage (Von) - NCD | 0.725 | V | Static forward characteristic (Device A) |
| Reverse Breakdown Voltage (VBR) - NCD | -164 | V | Limited by etching damage |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied heavily on precise MPCVD growth parameters and complex multi-step etching processes.
- Substrate & Epitaxy: Si-based AlGaN/GaN heterostructure (6-inch wafer) was used, featuring a 200 nm GaN channel and a 25 nm Al0.25Ga0.75N barrier layer.
- Ohmic Contact Formation: Ti/Al/Ni/Au multi-layer metal stack (20 nm/150 nm/50 nm/100 nm) deposited via Electron Beam Evaporation (EBE), followed by 835 °C annealing in pure N2.
- SiN Buffer Layer: A 50 nm SiN layer was deposited via ICP-CVD at 130 °C to protect the AlGaN/GaN interface from the high-energy hydrogen plasma during subsequent NCD growth.
- NCD Seeding: NCD seed suspension was applied via spin coating (1000 r/min for 10 s).
- MPCVD NCD Growth Recipe:
- Temperature: 650 °C
- Microwave Power: 3.2 kW
- Pressure: 135 mbar (1 mbar = 100 Pa)
- Gas Flows (Standard Conditions): H2 (300 mL/min), CH4 (12 mL/min), N2 (0.05 mL/min)
- Duration: 15 minutes
- Anode Etching (NCD Removal): A multi-step ICP dry etching process was used, including CF4-based etching (300 W/50 W) using a 100 nm SiN hard mask, followed by pure O2 ICP etching (600 W/300 W) to remove the NCD film over the anode region.
- Schottky Anode: Ni/Au metalization (20 nm/200 nm) deposited via EBE.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD specializes in providing the high-quality MPCVD diamond materials necessary to replicate and advance this critical research in GaN thermal management. Our capabilities directly address the material requirements and processing challenges outlined in this study.
Applicable Materials for GaN Integration
Section titled âApplicable Materials for GaN IntegrationâThe NCD film utilized in this study is a form of Polycrystalline Diamond (PCD). 6CCVD offers specialized PCD materials optimized for semiconductor integration:
- Thin-Film PCD (Nanocrystalline/Microcrystalline): We supply high-purity PCD films grown via MPCVD, ideal for direct deposition or integration onto GaN/SiC/Si substrates, matching the requirements for Device A passivation.
- Optical Grade SCD/PCD: For applications requiring diamond substrates for high-power Diamond-on-GaN architectures, our materials offer the highest intrinsic thermal conductivity (> 2000 W·m-1·K-1).
Customization Potential & Manufacturing Support
Section titled âCustomization Potential & Manufacturing Supportâ| Requirement from Paper | 6CCVD Capability | Technical Advantage |
|---|---|---|
| NCD Thickness (380-450 nm) | Custom SCD/PCD thickness from 0.1 ”m up to 500 ”m. | Allows researchers to precisely tune the NCD layer thickness for optimal thermal spreading and stress management. |
| Wafer Size (2 cm x 2 cm samples) | Custom plates/wafers up to 125 mm (PCD). | Supports scaling the NCD passivation strategy from R&D samples to commercial, inch-size GaN wafers. |
| Complex Metalization | Internal metalization capability: Au, Pt, Pd, Ti, W, Cu. | We provide pre-metalized diamond layers or custom metal stacks (e.g., Ti/Al/Ni/Au) to simplify device fabrication and ensure robust ohmic/Schottky contacts. |
| Surface Quality | SCD polishing to Ra < 1 nm; Inch-size PCD polishing to Ra < 5 nm. | Essential for minimizing Thermal Boundary Resistance (TBR) when integrating diamond as a substrate or heat spreader. |
| MPCVD Expertise | In-house PhD engineering team specializing in MPCVD growth recipes. | Our team can assist with material selection and process optimization (e.g., controlling grain size, purity, and stress) to achieve the specific thermal and electrical properties required for high-performance GaN SBDs. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team can assist with material selection and optimization for similar GaN Power Diode and HEMT projects. We provide consultation on:
- Optimizing diamond film properties (grain size, stress, and purity) to maximize thermal conductivity while maintaining low interface trap density for current collapse mitigation.
- Designing custom diamond substrates or films for integration via direct growth or bonding techniques.
- Selecting appropriate metalization schemes for robust, high-temperature operation.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Thermal accumulation under high output power density is one of the key bottlenecks faced by GaN-based power devices. The nanocrystalline diamond (NCD) passivation layer strategy plays a crucial role in improving heat dissipation in high-power GaN devices, while the existing studies focus on GaN-based HEMT. In this study, nanocrystalline diamond films with a thickness of 380-450 nm are grown on Si-based AlGaN/GaN heterostructure materials using a microwave plasma chemical vapor deposition (MPCVD) system. Consequently, lateral Schottky barrier diode devices with NCD passivation are fabricated, and their electrical and thermal properties are investigated. The results show that the DC forward characteristics of the NCD passivated diodes are essentially the same as those of devices without NCD passivation. Moreover, dynamic voltage tests indicate that the NCD passivation layer significantly mitigates current collapse in GaN devices at high frequencies. Under a -20 V DC bias and a pulse voltage of 2.5 V, the current density degradation of NCD passivated devices is only 2.6%, whereas devices without diamond passivation almost completely degrade. Thermal imaging microscopy under varying DC power levels shows that thermal failure occurs at an output power density of approximately 4 W/mm for conventional devices, while NCD passivated devices can reach around 7.5 W/mm. The electrical degradation behaviour of NCD passivated device is also tested under long-time reverse bias. This work demonstrates for the first time the application of nanocrystalline diamond passivation to thermal management of GaN-based power diodes, and clearly demonstrates the potential of this strategy in non-HEMT power device applications.