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6CCVD Research

Vertical Diamond p-n Junction Diode with Step Edge Termination Structure Designed by Simulation

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-08-26
JournalMicromachines
AuthorsGuangshuo Cai, Caoyuan Mu, Jiaosheng Li, Liuan Li, Shaoheng Cheng
InstitutionsJilin University, State Key Laboratory of Superhard Materials
Citations4
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

The research details the simulation and optimization of a vertical diamond p-n junction diode (PND) utilizing a hybrid edge termination (ET) structure to maximize breakdown voltage (VBD) and performance metrics.

  • Core Value Proposition: A novel hybrid structure combining a shallow Step Mesa ET with a Junction Termination Extension (JTE) effectively suppresses electric field crowding at the junction edge, which is the primary cause of premature breakdown in conventional diamond PNDs.
  • Performance Achievement: The optimized device achieved a VBD of 2100 V and an Ron of 0.411 mΩ·cm2, resulting in a Baliga’s Figure of Merit (BFOM) of 12.87 GW/cm2.
  • Structural Optimization: The optimal Step ET parameters were determined to be a width (W) of 1.0 ”m and a depth (D) of 0.5 ”m.
  • JTE Mechanism: High JTE doping (2 x 1022 cm-3) was critical. This high concentration ensured the depletion regions formed by the JTE overlapped with the main p-n junction depletion region, leading to a highly uniform electric field distribution across the drift layer.
  • Fabrication Consideration: The shallow step mesa approach (D < 1 ”m) was chosen over deep etching (D = 3 ”m, VBD = 1400 V) to balance high performance with the practical difficulties of deep etching hard, high-atomic-density diamond.
  • Comparison: The optimized hybrid device VBD (2100 V) is significantly higher than the conventional PND (900 V) and the simple Step ET PND (1200 V), moving closer to the theoretical ideal parallel-plane limit (3000 V).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Optimized Breakdown Voltage (VBD)2100VStep ET (W=1.0, D=0.5 ”m) + JTE (2 x 1022 cm-3)
On-Resistance (Ron)0.411mΩ·cm2Optimized device
Baliga’s Figure of Merit (BFOM)12.87GW/cm2Optimized device
Turn-On Voltage (Von)5.5VOptimized device
Simulation Temperature (T)550KUsed to ensure effective dopant ionization and low resistance
Critical Breakdown Field (Ec)6MV/cmSimulation parameter for diamond
Drift Layer Thickness (p-)5”mBase structure thickness
Drift Layer Doping (p-)1.5 x 1015cm-3Lightly doped layer
Cathode/Anode Doping (n+/p+)2.5 x 1020 / 2 x 1020cm-3Heavily doped contact layers
Optimal JTE Doping Concentration2 x 1022cm-3Required for depletion region overlap
Diamond Bandgap (Eg)5.5eVMaterial property
Thermal Conductivity (k)22W/(cm·K)Material property
Electron Mobility (Room T)4500cm2/(V·s)Material property

Key Methodologies

Section titled “Key Methodologies”

The device optimization was performed using Silvaco TCAD software (Version 5.0.10.R) focusing on structural and doping parameter variations.

  1. Device Structure Definition: A vertical PND structure was established: 500 nm p+ substrate, 5 ”m p- drift layer, and 500 nm n+ top layer.
  2. Physical Model Implementation: Key models were added to account for diamond’s unique properties: common phonon-assisted tunneling, Parallel-Electric-Field-dependent mobility, Selberherr’s ionization, and incomplete ionization.
  3. Thermal Calibration: The simulation temperature was set to 550 K (277 °C). This high temperature was necessary to overcome the large activation energies of diamond dopants (Acceptor Ea = 0.36 eV, Donor Ed = 0.57 eV) and ensure effective ionization, resulting in stable, low Ron.
  4. Simple Step ET Optimization: The width (W) and depth (D) of the simple step mesa were varied (e.g., (0.5, 0.5), (0.5, 1), (1, 0.5), (1, 1) ”m/”m). The optimal simple step (W=0.2 ”m, D=0.5 ”m) achieved a VBD of 1200 V.
  5. Hybrid JTE Integration: A p-n junction-based JTE was introduced onto the step mesa structure to further enhance VBD by expanding the depletion region laterally.
  6. JTE Doping Optimization: JTE doping concentration was varied from low (3 x 1018 cm-3) to high (2 x 1022 cm-3). High doping was found necessary to create a strong enough depletion effect to merge with the main p-n junction depletion region.
  7. Final Parameter Selection: The optimal hybrid structure was identified as W=1.0 ”m, D=0.5 ”m, combined with a JTE doping of 2 x 1022 cm-3, yielding the maximum VBD of 2100 V.

Commercial Applications

Section titled “Commercial Applications”

The development of high-performance vertical diamond PNDs with optimized edge termination structures is critical for next-generation power electronics and devices operating in extreme environments.

  • High-Power Switching Devices: Used in high-voltage applications where low static power loss (due to conductivity modulation) and high current handling capability are required, such as in smart grids and industrial motor drives.
  • High-Frequency/High-Power RF: Diamond’s exceptional thermal conductivity (22 W/(cm·K)) and high carrier mobility make these devices ideal for high-power microwave and radio frequency (RF) applications where heat dissipation is critical.
  • Harsh Environment Electronics: Suitable for use in extreme conditions (high temperature, strong radiation) found in aerospace, deep-sea exploration, and nuclear monitoring equipment.
  • Deep Ultraviolet (UV) Detectors: Leveraging diamond’s large bandgap (5.5 eV) and exciton binding energy (80 meV) for high-intensity, room-temperature UV detection, potentially for specialized sensing or sterilization equipment.
  • Power Conversion Systems: The high BFOM achieved (12.87 GW/cm2) indicates superior efficiency for high-voltage power converters and inverters.
View Original Abstract

In this paper, diamond-based vertical p-n junction diodes with step edge termination are investigated using a Silvaco simulation (Version 5.0.10.R). Compared with the conventional p-n junction diode without termination, the step edge termination shows weak influences on the forward characteristics and helps to suppress the electric field crowding. However, the breakdown voltage of the diode with simple step edge termination is still lower than that of the ideal parallel-plane one. To further enhance the breakdown voltage, we combine a p-n junction-based junction termination extension on the step edge termination. After optimizing the structure parameters of the device, the depletion regions formed by the junction termination extension overlap with that of the p-n junction on the top mesa, resulting in a more uniform electric field distribution and higher device performance.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2014 - Diamond Schottky barrier diode for high-temperature, high-power, and fast switching applications [Crossref]
  2. 2014 - 600 V Diamond Junction Field-Effect Transistors Operated at 200 °C [Crossref]
  3. 2014 - Diamond Metal-Semiconductor Field-Effect Transistor With Breakdown Voltage Over 1.5 kV [Crossref]
  4. 2002 - High carrier mobility in single-crystal plasma-deposited diamond [Crossref]
  5. 2011 - ZnO-Microrod/p-GaN Heterostructured Whispering-Gallery-Mode Microlaser Diodes [Crossref]
  6. 2002 - An effective high-voltage termination for SiC planar pn junctions for use in high-voltage devices and UV detectors
  7. 2022 - TCAD Analysis of O-Terminated Diamond m-i-p+ Diode Characteristics Dependencies on Surface States CNL and Metal-Induced Gap States [Crossref]
  8. 2016 - Temperature dependent simulation of diamond depleted Schottky PIN diodes [Crossref]
  9. 2009 - Rectifying properties and photoresponse of CVD diamond p(i)n-junctions [Crossref]

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