Mobility Models Based on Forward Current-Voltage Characteristics of P-type Pseudo-Vertical Diamond Schottky Barrier Diodes

At a Glance

Metadata	Details
Publication Date	2020-06-18
Journal	Micromachines
Authors	Min-Woo Ha, Ogyun Seok, Hojun Lee, Hyun Ho Lee
Institutions	Korea Electrotechnology Research Institute, Myongji University
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: P-type Pseudo-Vertical Diamond SBDs

Executive Summary

This research validates the critical role of hole mobility modeling in optimizing the performance of p-type pseudo-vertical diamond Schottky Barrier Diodes (SBDs) for high-power switching applications.

High Performance Achieved: Numerical simulations, optimized using the Empirical Mobility Model, demonstrated exceptional performance metrics suitable for replacing Si and SiC devices.
Key Metrics: The optimized device achieved a low specific on-resistance (R_on,sp) of 6.8 mΩ·cm², a high breakdown voltage (V_B) of 1190 V, and a high Figure-of-Merit (FOM) of 210 MW/cm².
Material Requirement: The device relies on high-quality, low-doped p-type diamond (N_a = 10¹⁵ cm^-3) for the 4.6 µm drift layer to maximize V_B.
Mobility Model Insight: The Lombardi CVT model proved essential for high-field simulations, as it accurately accounts for mobility degradation caused by electric field concentration, particularly at the Schottky contact edge.
Geometric Optimization: Performance was highly dependent on the p- drift layer thickness (t_drift) and the cathode contact length (l_cathode), confirming the need for precise material dimensioning.
6CCVD Value Proposition: The successful replication and extension of this research requires ultra-high-quality, custom-thickness, Boron-Doped Diamond (BDD) wafers and precision metalization, all available through 6CCVD’s MPCVD capabilities.

Technical Specifications

Parameter	Value	Unit	Context
Specific On-Resistance (R_on,sp)	6.8	mΩ·cm²	Optimized device performance (Empirical Model)
Breakdown Voltage (V_B)	1190	V	Optimized device performance
Figure-of-Merit (FOM)	210	MW/cm²	Calculated as V_B² / R_on,sp
Forward Voltage Drop (V_f)	1.77	V	@ 100 A/cm², 300 K (Empirical Model)
P- Drift Layer Thickness (t_drift)	4.6	µm	Optimized geometry for V_B
P- Drift Layer Doping (N_a)	10¹⁵	cm^-3	Low doping concentration
Hole Saturation Velocity (v_sat)	2.7 x 10⁷	cm/s	Fixed simulation parameter
Schottky Contact Material	Platinum (Pt)	N/A	Used for cathode contact
Metal Work Function (Φ_m)	5.65	eV	Platinum contact parameter
Built-in Potential	1.1	V	@ 300 K
Operating Temperature Range	200 - 500	K	Range tested for mobility models

Key Methodologies

The study utilized the Silvaco Atlas numerical simulation tool to investigate the forward I-V characteristics and breakdown voltage of the p-type pseudo-vertical diamond SBD.

Device Structure: A pseudo-vertical SBD geometry was defined, featuring a p- drift layer (t_drift) and a highly doped p+ layer on a diamond substrate.
Material Parameters: Standard diamond semiconductor parameters were fixed, including a wide band gap of 5.5 eV and a room temperature density of states in the valence band of 5 x 10¹⁹ cm^-3.
Doping Control: The p- drift layer doping concentration (N_a) was set to a low value of 10¹⁵ cm^-3 to ensure a high breakdown voltage capability.
Schottky Contact: Platinum (Pt) was selected for the Schottky contact (cathode) due to its high metal work function (5.65 eV), resulting in a Schottky barrier height of 1.35 eV.
Mobility Model Comparison: Four distinct hole mobility models were applied and compared to assess their impact on V_f and R_on,sp:
- Constant Mobility: Dependent only on acoustic phonon scattering due to temperature.
- Analytic Mobility: Dependent on temperature and doping concentration.
- Lombardi CVT: Dependent on concentration, voltage, temperature, and crucial for modeling electric field-dependent mobility degradation.
- Empirical Mobility: Based on external experimental results (Volpe et al.), providing the best fit for low-field operation.
Geometric Optimization: The device performance was systematically analyzed by varying the p- drift layer thickness (t_drift) from 3.0 µm to 6.0 µm and the Schottky contact length (l_cathode) from 0.5 µm to 3.0 µm to maximize V_B while minimizing R_on,sp.

6CCVD Solutions & Capabilities

This research highlights the need for precision-engineered, high-quality diamond materials to realize next-generation power devices. 6CCVD is uniquely positioned to supply the required materials and services to replicate and advance this work.

Applicable Materials

The high breakdown voltage (1190 V) and low R_on,sp achieved in this study depend critically on the quality and precise doping of the diamond drift layer.

Research Requirement	6CCVD Material Solution	Technical Advantage
P-type Drift Layer (N_a = 10¹⁵ cm^-3)	Lightly Boron-Doped Diamond (BDD)	Ultra-low defect density SCD/PCD ensures high carrier mobility and minimizes leakage current, crucial for achieving high V_B.
High Quality Substrate (p+)	Heavy Boron-Doped Diamond (BDD)	Available as highly conductive substrates (up to 10mm thick) to minimize series resistance in the vertical current path.
High Surface Quality	Optical Grade SCD	Polishing capability to Ra < 1nm ensures minimal surface roughness, critical for reliable metalization and minimizing scattering effects.

Customization Potential for Power Device Fabrication

The simulation results emphasize that device performance is highly sensitive to geometric parameters (t_drift and l_cathode) and contact metallurgy. 6CCVD offers full customization to meet these stringent requirements:

Custom Thickness Control: The optimized drift layer thickness of 4.6 µm is well within 6CCVD’s standard SCD/PCD thickness range (0.1 µm to 500 µm). We provide precise thickness control necessary for V_B tuning.
Precision Metalization: The device requires a Platinum (Pt) Schottky contact. 6CCVD offers internal, high-purity metalization services, including Pt, Au, Ti, Pd, W, and Cu, tailored to specific contact geometries and adhesion requirements.
Large Area PCD: While this study focused on a small pseudo-vertical structure, 6CCVD can supply Polycrystalline Diamond (PCD) wafers up to 125mm in diameter, enabling scaling for commercial high-power modules.
Precision Patterning: Custom laser cutting and patterning services are available to define the precise cathode length (l_cathode = 2.0 µm) and overall device dimensions required for optimal current density and depletion region control.

Engineering Support

The comparison of mobility models (Analytic vs. Lombardi CVT vs. Empirical) demonstrates the complexity of simulating diamond power devices. 6CCVD’s in-house PhD engineering team specializes in diamond material science and device physics.

Application Expertise: We provide consultation on material selection (SCD vs. PCD, doping levels, and defect management) for high-power switching, high-temperature electronics, and high-frequency applications.
Mobility Enhancement: Our team can assist researchers in selecting the optimal diamond growth parameters (MPCVD recipe) to maximize hole mobility, directly impacting the achievable R_on,sp and V_f.

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

View Original Abstract

Compared with silicon and silicon carbide, diamond has superior material parameters and is therefore suitable for power switching devices. Numerical simulation is important for predicting the electric characteristics of diamond devices before fabrication. Here, we present numerical simulations of p-type diamond pseudo-vertical Schottky barrier diodes using various mobility models. The constant mobility model, based on the parameter μconst, fixed the hole mobility absolutely. The analytic mobility model resulted in temperature- and doping concentration-dependent mobility. An improved model, the Lombard concentration, voltage, and temperature (CVT) mobility model, considered electric field-dependent mobility in addition to temperature and doping concentration. The forward voltage drop at 100 A/cm2 using the analytic and Lombard CVT mobility models was 2.86 and 5.17 V at 300 K, respectively. Finally, we used an empirical mobility model based on experimental results from the literature. We also compared the forward voltage drop and breakdown voltage of the devices, according to variations in p- drift layer thickness and cathode length. The device successfully achieved a low specific on-resistance of 6.8 mΩ∙cm2, a high breakdown voltage of 1190 V, and a high figure-of-merit of 210 MW/cm2.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi11060598

References

2002 - High Carrier Mobility in Single-Crystal Plasma-Deposited Diamond [Crossref]
2016 - Optimal drift region for diamond power devices [Crossref]
2016 - Diamond field-effect transistors for RF power electronics: Novel NO2 hole doping and low-temperature deposited Al2O3 passivation [Crossref]
2020 - Degradation of forward current density with increasing blocking voltage in diamond Schottky-pn diodes [Crossref]
2019 - Performance Improved Vertical Diamond Schottky Barrier Diode with Fluorination-Termination Structure [Crossref]
2016 - Inversion channel diamond metal-oxide-semiconductor with normally-off characteristics [Crossref]
2020 - Effect of Annealing Temperature on Performances of Boron-Doped Diamond Metal-Semiconductor Field-Effect Transistors [Crossref]
2020 - High temperature (300 °C) ALD grown Al2O3 on hydrogen terminated diamond: Band offset and electrical properties of the MOSFETs [Crossref]
2019 - Polishing, preparation and patterning of diamond for device applications [Crossref]
2020 - An Enhancement-Mode Hydrogen-Terminated Diamond Field-Effect Transistor with Lanthanum Hexaboride Gate Material [Crossref]