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	Myongji University, Korea Electrotechnology Research Institute
Citations	7
Analysis	Full AI Review Included

Executive Summary

This study presents numerical simulations of p-type pseudo-vertical Diamond Schottky Barrier Diodes (SBDs) to optimize forward current-voltage (I-V) characteristics and breakdown voltage (BV) for power switching applications.

Core Value Proposition: Diamond SBDs offer superior performance (wide band gap, high critical field, high thermal conductivity) compared to Si and SiC for high-power, high-temperature electronics.
Mobility Model Impact: Four hole mobility models (Constant, Analytic, Lombardi CVT, Empirical) were compared, showing that the choice of model significantly affects simulated performance metrics (Vf and R_on,sp).
Lombardi CVT Limitation: The Lombardi CVT model, which accounts for electric field dependence, predicted severe mobility degradation and resulted in the highest forward voltage drop (Vf = 5.17 V at 300 K).
Empirical Model Suitability: The Empirical mobility model, based on experimental results from the literature, was deemed the most suitable for low-field numerical simulation, yielding a Vf of 1.77 V at 300 K.
Optimized Performance: The optimized device structure (4.6 µm drift layer, 2.0 µm cathode length) achieved a low Specific On-Resistance (R_on,sp) of 6.8 mΩ·cm².
High Figure-of-Merit (FOM): The device demonstrated a high BV of 1190 V, resulting in an exceptional Figure-of-Merit (FOM = BV²/R_on,sp) of 210 MW/cm².

Technical Specifications

Parameter	Value	Unit	Context
Semiconductor Material	Diamond (p-type)	N/A	Single-crystal CVD
Band Gap (E_g)	5.5	eV	Material property
Thermal Conductivity	22	W/cm/K	Highest of any material on Earth
Critical Breakdown Field	> 10	MV/cm	Enables thin drift layers
p- Drift Layer Doping (N_a)	10¹⁵	cm^-3	Used for high BV design
p- Drift Layer Thickness (t_drift)	4.6	µm	Optimized geometry
Schottky Contact Metal	Platinum (Pt)	N/A	Metal Work Function (Φ_m) = 5.65 eV
Schottky Barrier Height (Φ_b)	1.35	eV	Calculated/Simulated
Hole Saturation Velocity (v_sat)	2.7 x 10⁷	cm/s	Fixed simulation parameter
Target Current Density (J_f)	100	A/cm²	Used for V_f extraction
Optimized Specific On-Resistance (R_on,sp)	6.8	mΩ·cm²	Empirical model, 300 K
Optimized Forward Voltage Drop (V_f)	1.77	V	Empirical model, 300 K, 100 A/cm²
Optimized Breakdown Voltage (BV)	1190	V	t_drift = 4.6 µm
Figure-of-Merit (FOM)	210	MW/cm²	(BV)² / R_on,sp
Analytic Mobility R_on,sp	17.5	mΩ·cm²	At 300 K
Lombardi CVT R_on,sp	40.8	mΩ·cm²	At 300 K (Highest resistance)

Key Methodologies

The study utilized the Silvaco Atlas numerical simulation tool to model the electrical characteristics of the p-type diamond pseudo-vertical SBD.

Device Definition: The structure was defined using fixed material parameters for diamond, including a band gap of 5.5 eV, affinity of 1.5 eV, and a p- drift layer doping concentration (N_a) of 10¹⁵ cm^-3.
Schottky Contact: Platinum (Pt) was used for the Schottky contact (cathode) with a metal work function of 5.65 eV, resulting in a Schottky barrier height of 1.35 eV.
Mobility Model Implementation: Four distinct hole mobility models were implemented and compared to assess their influence on I-V characteristics:
- Constant Model: Mobility (µ_p) fixed absolutely at 300 K (e.g., 2000 cm²/Vs) and scaled only by temperature (T^-1.5 dependence).
- Analytic Model: Accounts for temperature and doping concentration dependence, considering acoustic phonon and ionized impurity scattering.
- Lombardi CVT Model: An improved model considering temperature, doping concentration, and the perpendicular electric field (voltage), leading to mobility degradation in high-field regions (e.g., near the Schottky contact edge).
- Empirical Model: Based on experimental results from Volpe et al., incorporating temperature and doping dependence, suitable for low on-current density simulation.
Breakdown Simulation: The reverse characteristics were modeled using Selberherr’s impact ionization model, with fitting parameters modified to ensure the breakdown field satisfied the 10 MV/cm requirement for parallel-plane diamond SBDs.
Geometric Optimization: Forward voltage drop (V_f) and breakdown voltage (BV) were systematically analyzed by varying the p- drift layer thickness (t_drift: 3.0 to 6.0 µm) and the Schottky contact (cathode) length (l_cathode: 0.5 to 3.0 µm).

Commercial Applications

Diamond power devices, due to their extreme material properties (high BV, low R_on,sp, high thermal conductivity), are positioned to replace conventional Si and SiC devices in demanding applications.

High-Power Switching Systems: Ideal for applications requiring high energy conversion efficiency and low power loss, such as industrial motor drives and large-scale power converters.
Electric Grid Infrastructure: Suitable for high-voltage DC (HVDC) transmission and smart grid components where high breakdown voltage (> 1 kV) and reliability are critical.
Aerospace and Defense: Used in systems requiring robust, high-temperature electronics that must operate reliably in harsh environments without complex cooling systems.
Automotive Power Electronics: Potential use in electric vehicle (EV) charging systems and power management units where high efficiency and compact size are essential.
High-Frequency Inverters/Rectifiers: The low specific on-resistance enables high current handling with minimal resistive losses, improving the performance of high-frequency power supplies.

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

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