Diamond p-Type Lateral Schottky Barrier Diodes With High Breakdown Voltage (4612 V at 0.01 mA/Mm)

At a Glance

Metadata	Details
Publication Date	2023-08-31
Journal	IEEE Electron Device Letters
Authors	Zhuoran Han, C. Bayram
Institutions	University of Illinois Urbana-Champaign
Citations	26
Analysis	Full AI Review Included

Executive Summary

This analysis summarizes the fabrication and performance of diamond p-type lateral Schottky Barrier Diodes (SBDs) designed for high-power electronics.

Record Breakdown Voltage: The SBD achieved a stable reverse breakdown voltage (V_br) of 4612 V, measured at a leakage current density less than 0.01 mA/mm. This is among the highest reported V_br for p-type diamond SBDs.
Field Plate Effectiveness: The integration of a 300 nm Al₂O₃ field plate (FP) was critical, increasing the V_br from 1159 V (without FP) to 4612 V (with FP). TCAD simulations confirmed the FP reduced the peak electric field near the Schottky contact edge by 56%.
Lateral Configuration: The device utilizes a lateral configuration, allowing V_br scaling by adjusting the anode-cathode distance (80 µm) without requiring challenging thick drift layer growth necessary for vertical devices.
High Rectification and Temperature Stability: Both diodes exhibited a high rectifying ratio (greater than 10⁷) at room temperature. At 200 °C, the forward current density increased significantly to 5.39 mA/mm (at 40 V), demonstrating high-temperature operation capability.
Specific On-Resistance (R_ON): The R_ON was measured at 527 Ω-cm² (with FP). While high compared to theoretical limits, this is attributed primarily to space charge limited conduction (SCLC) due to the lightly doped drift layer and incomplete dopant ionization.

Technical Specifications

Parameter	Value	Unit	Context
Peak Breakdown Voltage (V_br)	4612	V	With Al₂O₃ Field Plate (FP)
V_br (Baseline)	1159	V	Without Al₂O₃ FP
Leakage Current Density (J_L)	< 0.01	mA/mm	Stable up to 4612 V
Specific On-Resistance (R_ON)	527	Ω-cm²	With FP
Rectifying Ratio	> 10⁷	N/A	At room temperature (RT)
Schottky Barrier Height (SBH)	1.02 ± 0.01	eV	Mo/Diamond contact
Specific Ohmic Contact Resistance (R_c)	1.25 ± 0.98 x 10^-4	Ω-cm²	Ti/Pt/Au contact
Peak Forward Current Density (J_F)	5.39	mA/mm	At 40 V forward bias, 200 °C
Drift Layer Thickness (t)	2	µm	p^- layer
Drift Layer Doping ([B])	< 8 x 10¹⁵	cm^-3	p^- layer
Ohmic-Schottky Distance (d)	80	µm	Lateral separation
Field Plate Dielectric Constant (k)	8.63 ± 0.07	N/A	As-deposited Al₂O₃
Surface Roughness (RMS)	7.5	nm	Epitaxial layer

Key Methodologies

The diamond p-type lateral SBDs were fabricated using Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) and standard cleanroom microfabrication techniques.

Epitaxial Growth:
- A 2 µm p^- drift layer (Boron concentration [B] < 8 x 10¹⁵ cm^-3) was grown on a 3 x 3 mm² Type Ib (100) HPHT diamond substrate.
- A 200 nm p⁺ layer ([B] ~ 3 x 10²⁰ cm^-3) was selectively grown to define the ohmic contact region.
Ohmic Contact Formation:
- Metal stack: Ti (30 nm) / Pt (30 nm) / Au (100 nm) deposited via e-beam evaporation.
- Annealing: Thermal annealing performed at 450 °C in an Argon (Ar) ambient for 50 minutes.
Field Plate Deposition:
- Material: 300 nm Al₂O₃ deposited via e-beam evaporation.
- Purpose: Al₂O₃ was chosen for its high dielectric constant (k ≈ 8.63) to reduce electric field strength and provide a large band offset.
Surface Termination:
- The exposed diamond surface was treated with ozone at room temperature for 1.5 hours to achieve a stable oxygen termination prior to Schottky contact deposition.
Schottky Contact Deposition:
- Metal stack: Mo (50 nm) / Pt (50 nm) / Au (100 nm) deposited via e-beam evaporation.

Commercial Applications

The demonstrated high breakdown voltage and high-temperature capability of diamond SBDs position this technology for use in extreme environment and high-efficiency power systems.

High-Voltage Power Conversion:
- Power Grids and Substations: Diamond SBDs can replace silicon or SiC diodes in high-voltage DC-DC converters and rectifiers, offering lower losses due to diamond’s superior critical electric field (E_B).
- Electric Vehicles (EVs) and Charging Infrastructure: Used in high-power fast chargers and onboard power electronics where high V_br and thermal stability are critical for compact, efficient designs.
Aerospace and Defense:
- Extreme Environment Electronics: Diamond’s high thermal conductivity (k) and wide bandgap (E_G) allow operation at high temperatures (demonstrated 200 °C) and high radiation environments without significant degradation.
Pulsed Power Systems:
- The high V_br makes these devices suitable for applications requiring rapid switching and handling of large voltage spikes, such as radar and directed energy systems.
Industrial Motor Drives:
- High-efficiency motor control systems requiring robust power switching components capable of handling high voltages and high junction temperatures.

View Original Abstract

Diamond p-type lateral Schottky barrier diodes (SBDs) with a 2-μm-thick drift layer are fabricated with and without Al2O3 field plates. Schottky contacts composed of Mo (50 nm) / Pt (50 nm) / Au (100 nm) showed a barrier height of 1.02 ± 0.01 eV and ohmic contacts of Ti (30 nm) / Pt (30 nm) / Au (100 nm) achieved a specific ohmic contact resistance of 1.25 ± 0.98 × 10-4 Ω-cm2. Their forward and reverse bias characteristics are studied in detail. Both SBDs, with and without Al2O3 field plates, exhibit rectifying ratios larger than 107 at room temperature, and a peak current density of 5.39 mA/mm under 40 V forward bias at 200 °C. The leakage current density at room temperature is stable at approximately 0.01 mA/mm for both diodes. The SBD without the Al2O3 field plate exhibited a breakdown voltage of 1159 V, while the SBD with the Al2O3 field plate is stable under a reverse voltage of 4612 V, which is higher than many diamond SBDs previously reported.

Tech Support

Original Source

DOI: https://doi.org/10.1109/led.2023.3310910