CHARACTERIZATION OF THE VERY LOW CONTACT RESISTANCE ON HEAVILY BORON DOPED (113) CVD DIAMOND
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | NANOCOM ⊠|
| Authors | J. Voves, Alexandr Laposa, Z. Ć obĂĄĆ, P. Hazdra, VojtÄch PovolnĂœ |
| Institutions | Czech Academy of Sciences, Institute of Physics, Czech Technical University in Prague |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research characterizes ultra-low resistance ohmic contacts on heavily boron-doped (113) CVD diamond, a critical step for developing high-efficiency diamond power electronic devices.
- Core Achievement: Demonstrated specific contact resistance (RCsp) values around 10-6 Ω.cm2 on (113) BDD, reaching the resolution limit of the cTLM measurement setup used.
- Material Platform: Utilized (113) oriented epitaxial diamond layers, which provide superior surface morphology and lower roughness compared to standard (100) and (111) orientations, enhancing device performance.
- Contact System: Titanium/Gold (Ti/Au) contacts (10 nm Ti / 100 nm Au) were employed, confirming stable ohmic behavior and good thermal stability up to 700 °C annealing temperatures.
- Transport Mechanism: The low resistance is attributed to the high boron doping levels (up to 1021 cm-3), enabling efficient charge transfer primarily via field emission (tunneling).
- Validation Methodology: Experimental Circular Transmission Line Model (cTLM) data were rigorously corrected for large gap spacing (d/L ratio) and validated using both analytical models (Thermionic Field Emission/Field Emission) and Silvaco TCAD 2D simulations.
- Engineering Insight: TCAD simulations were necessary to quantify and account for measurement errors introduced by the finite resistivity of the metal layer, which becomes comparable to the highly conductive diamond sheet resistance.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Lowest Specific Contact Resistance (RCsp) | ~10-6 | Ω.cm2 | Achieved value, limited by measurement resolution. |
| Diamond Orientation | (113) | N/A | Epitaxial layer growth platform. |
| Boron Doping Concentration (Na) Range | 1019 to 1021 | cm-3 | Concentration in the BDD epilayer. |
| Ti Contact Layer Thickness | 10 | nm | Ohmic contact layer. |
| Au Capping Layer Thickness | 100 | nm | Used for thermal stability and capping. |
| Annealing Temperature | Up to 700 | °C | Post-metallization thermal treatment. |
| CVD Reactor Power | 700 | W | Microwave Plasma Enhanced CVD (MWPECVD). |
| CVD Pressure | 100 | mbar | Growth condition. |
| Methane Concentration (CH4) | 1 | % | Growth condition. |
| Inner Circle Radius (L) | 75 | ”m | cTLM pattern dimension. |
| Electrode Gap Spacing (d) Range | 10 to 75 | ”m | cTLM pattern dimension. |
| Diamond Relative Permittivity (Δr) | 5.5 | N/A | Used in analytical modeling [9]. |
| Hole Effective Mass (m*h) | 0.908 m0 | N/A | Used for field emission calculations [8]. |
| Valence Band Density of States (NV) | 1019 | cm-3 | At room temperature (300 K) [8]. |
| Calculated Barrier Height (Ίb) | 0.4 | eV | Consistent with experimental data at lower doping levels [11]. |
Key Methodologies
Section titled âKey Methodologiesâ- BDD Epitaxial Growth: Heavily boron-doped diamond layers were grown on (113) oriented substrates using a commercial Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) reactor (AX5010).
- Doping Control: Boron concentration (1019 to 1021 cm-3) was controlled by varying the B/C ratio in the gas phase from 100 to 2000 ppm.
- Surface Characterization: Surface morphology and layer thickness were determined using Atomic Force Microscopy (AFM) and cross-section Scanning Electron Microscopy (X-SEM).
- Electrical Material Characterization: Resistivity, carrier concentration, and mobility were measured at room temperature using the Hall effect.
- Contact Patterning: Circular Transmission Line Model (cTLM) patterns (L=75 ”m, d=10 to 75 ”m) were defined using laser lithography and wet chemical etching.
- Metallization and Annealing: Ti (10 nm) / Au (100 nm) contacts were evaporated onto an ozone-treated (113) surface and subsequently annealed at temperatures up to 700 °C.
- Resistance Measurement: Current-voltage (I-V) characteristics were measured using the Kelvin method with a Cascade Microtech M150 probing system.
- cTLM Data Correction: The total measured resistance (RT) was corrected using an analytical correction factor (C) to ensure linear behavior for large gap spacings (d), allowing accurate extraction of sheet resistance (Rsh) and transfer length (LT).
- Analytical Modeling: The specific contact resistance (RCsp) was modeled using the parallel combination of Thermionic Field Emission (TFE) and Field Emission (FE) models, incorporating image force barrier lowering and Fermi level position dependence on doping.
- TCAD Simulation: Silvaco TCAD 2D simulation was performed to estimate the measurement error associated with the finite resistivity of the Ti/Au metal layer, which deviates from the ideal assumption of zero metal resistance.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful demonstration of ultra-low contact resistance on (113) BDD is crucial for advancing diamond-based semiconductor technology in several high-demand sectors:
- High-Power Switching Devices: Fabrication of high-performance diamond power electronic devices (e.g., MOSFETs, Schottky diodes) requiring minimal ON-state resistance (RON) for maximum efficiency.
- High-Voltage Systems: Components for future high-voltage applications where diamondâs superior breakdown field is leveraged, requiring low contact resistance to manage high current densities.
- High-Temperature Electronics: Utilization of the thermally stable Ti/Au contact system (stable up to 700 °C) enables reliable operation in extreme environments or high-temperature processing stages.
- Advanced Semiconductor Manufacturing: Establishing the (113) orientation as a viable and superior platform for commercial diamond device fabrication due to its improved surface quality and resulting lower contact resistance compared to current industry standards ((100) or (111)).
View Original Abstract
The low resistance of ohmic contacts on diamond layers is important for the fabrication of diamond power electronic devices with fast switching capabilities for future high voltage applications.The low barrier height between the metal and diamond, high level of boron doping and annealing at elevated temperatures are the most critical parameters to reach the lowest contact resistivity.In this work, we report on titanium/gold ohmic contacts prepared on the heavily boron-doped (113) epitaxial diamond layers.The contact resistance has been characterized by the Circular Transmission Line Model (cTLM) structures.We used the analytical model of field enhanced emission, tunneling and the image force influence including Fermi level position dependence on the boron concentration for theoretical Ti/Au contact analysis and the Silvaco TCAD 2D simulation to estimate the measurement error associated with the nonzero metal resistance.We show that the resulting simulation values are consistent with the experimental results.