Schottky Barrier Diodes Based on Freestanding Polycrystalline Diamond Membranes

At a Glance

Metadata	Details
Publication Date	2025-10-23
Journal	Advanced Electronic Materials
Authors	Dmitry Shinyavskiy, Chenyu Wang, L. J. Suter, Matthias Muehle, Jung‐Hun Seo
Institutions	University at Buffalo, State University of New York, Fraunhofer USA
Analysis	Full AI Review Included

Technical Documentation & Analysis: Vertical Schottky Barrier Diodes on Freestanding PCD Membranes

This document analyzes the research demonstrating vertical Schottky barrier diodes fabricated on freestanding Polycrystalline Diamond Membranes (PCDm). The findings validate the use of MPCVD PCD as a scalable, high-performance wide-bandgap semiconductor platform, directly aligning with 6CCVD’s core material and processing capabilities.

Executive Summary

Novel Architecture: First successful demonstration of vertical Schottky barrier diodes utilizing freestanding, transferable Polycrystalline Diamond Membranes (PCDm).
Performance Benchmark: Achieved an excellent On/Off ratio of ≈10³ and a high breakdown field of 0.25 MV cm⁻¹, surpassing previously reported values for PCD-based Schottky diodes.
Surface-Selective Contacting: The vertical architecture leverages the intrinsic structural asymmetry of the PCDm, enabling distinct contact optimization:
- Schottky contact (Mo) on the high-quality, large-grain, high sp³ growth surface.
- Ohmic contact (Ti/Au) on the smoother, sp²-rich nucleation (bottom) surface.
Material Basis: Devices were fabricated using a 3.5 µm thick, boron-doped PCD film grown via Microwave Plasma-Enhanced Chemical Vapor Deposition (MPECVD).
Scalability and Integration: The freestanding PCDm format addresses limitations of conventional thin-film PCD by enabling dual-side processing and facilitating easy heterogeneous integration for next-generation, cost-effective power electronics.

Technical Specifications

The following hard data points were extracted from the electrical and morphological characterization of the vertical PCDm Schottky diodes:

Parameter	Value	Unit	Context
Material Type	Boron-Doped PCD	N/A	Freestanding Membrane (PCDm)
PCDm Thickness (Final)	3.5	µm	Optimized for vertical transport
Breakdown Field (V_BR)	0.25	MV cm⁻¹	Measured at 20 °C (Highest reported for PCD)
On/Off Ratio (+5V)	≈10³ (1027.10 Avg)	N/A	Measured at 20 °C, demonstrating strong rectification
Schottky Barrier Height (Φ_B)	1.06	eV	Extracted via Richardson plot
Built-in Potential (V_bi)	0.98	V	Extracted from C-V measurements (100 kHz)
Ideality Factor (n)	1.47	N/A	Measured at 20 °C (Suggests thermionic emission dominance)
Sheet Resistance (R_s)	37	Ω/	Bottom surface (Ti/Au ohmic contact)
Contact Resistance (R_c)	27	Ω	Bottom surface (Ti/Au ohmic contact)
Top Surface Roughness (RMS)	≈98	nm	High crystallinity, large grains (≈1200 nm)
Bottom Surface Roughness (RMS)	≈5.5	nm	Smoother nucleation surface, small grains (≈500 nm)
Schottky Metal	Molybdenum (Mo)	N/A	Cathode (200 nm thick)
Ohmic Metal	Titanium/Gold (Ti/Au)	N/A	Anode (10/150 nm thick)

Key Methodologies

The fabrication of the vertical PCDm Schottky diode relies on precise MPCVD growth, advanced etching, and dual-side processing techniques:

PCD Film Growth: Boron-doped PCD thin film synthesized via Microwave Plasma-Enhanced Chemical Vapor Deposition (MPECVD) on (100) Si/SiO₂ wafers.
Masking and Patterning: A bi-layer metal etching mask (Cr/Ni) was deposited via photolithography to define the membrane structure.
PCD Etching: Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE) using a gas mixture of O₂ and CF₄ (4:1 ratio) was employed to etch the PCD layer.
Membrane Release: The underlying sacrificial SiO₂ layer was removed using 49% Hydrofluoric Acid (HF), resulting in the release of the freestanding PCD membrane (PCDm).
Transfer and Flip: The PCDm was flip-transferred onto a temporary SU-8-coated Si substrate using micro-transfer printing, exposing the bottom (nucleation) surface.
Bottom Surface Preparation: A brief 1 min RIE-ICP etching step was performed on the bottom surface to remove residual Si, achieving the final 3.5 µm thickness.
Ohmic Contact (Anode): Ti/Au (10/150 nm) was deposited on the bottom (sp²-rich) surface via electron-beam evaporation, confirmed to form a good ohmic contact (R_s = 37 Ω/).
Schottky Contact (Cathode): 200 nm Molybdenum (Mo) was deposited on the top (sp³-rich) growth surface using a shadow mask and sputtering system.

6CCVD Solutions & Capabilities

The successful fabrication of high-performance vertical PCD diodes requires precise control over material properties, thickness, doping, and metalization—all core competencies of 6CCVD. We are uniquely positioned to supply the materials and services necessary to replicate, scale, and advance this research.

Applicable Materials

To replicate or extend this research, the following 6CCVD materials are required:

Heavy Boron-Doped Polycrystalline Diamond (BDD): Essential for achieving the low sheet resistance (R_s = 37 Ω/) required for efficient ohmic contact formation on the nucleation side. Our MPCVD process ensures precise, uniform boron incorporation.
Optical Grade PCD: While the paper focused on electronic properties, the high crystalline quality of the growth surface (high sp³ content) is analogous to our high-quality PCD films, suitable for both electronic and optoelectronic applications (e.g., solar-blind photodetectors).

Customization Potential

6CCVD’s in-house manufacturing capabilities directly address the specific dimensional and processing requirements demonstrated in this vertical device architecture:

Research Requirement	6CCVD Capability	Technical Advantage
Custom Thickness (3.5 µm)	SCD/PCD Thickness Control: We routinely grow films from 0.1 µm up to 500 µm thick, ensuring precise replication of the 3.5 µm PCDm layer.	Guarantees accurate control over the vertical carrier transport path and electric field distribution.
Large-Area Scalability	PCD Wafers up to 125 mm: We offer PCD plates and wafers up to 125 mm in diameter, enabling industrial-scale fabrication far beyond the small membranes used in the study.	Facilitates the transition of this vertical architecture into commercial, large-area power electronics platforms.
Advanced Metalization	Custom Dual-Side Metalization: We offer internal deposition of all metals used (Ti, Au, Mo) plus Pt, Pd, W, and Cu. We support dual-side patterning and deposition for vertical devices.	Eliminates the need for external processing steps, ensuring high-quality, clean interfaces critical for both the Mo Schottky contact and the Ti/Au ohmic contact.
Surface Engineering	Ultra-Low Roughness Polishing: We provide polishing services to achieve Ra < 5 nm on inch-size PCD. We can specifically tailor the nucleation surface (bottom side) roughness for optimal metal adhesion and ohmic performance.	Ensures the necessary smooth surface (Ra ≈ 5.5 nm) for reliable metal-semiconductor interface formation, crucial for high-performance vertical diodes.

Engineering Support

The successful fabrication of these vertical devices hinges on managing the asymmetric properties of the PCD film (sp³-rich growth side vs. sp²-rich nucleation side). 6CCVD’s in-house PhD team specializes in wide-bandgap material science and can provide expert consultation on:

Material Selection: Optimizing Boron-Doped PCD growth parameters (doping concentration, grain structure) to maximize breakdown field and minimize series resistance.
Vertical Architecture Design: Assisting engineers with material selection and processing recipes for similar high-power electronic devices and solar-blind photodetectors requiring dual-side access and high thermal stability.
Transfer and Integration: Providing support for the transfer and integration of thin PCD films onto foreign or flexible substrates, leveraging the membrane format for hybrid device architectures.

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

View Original Abstract

Abstract Polycrystalline diamond (PCD) thin films have been widely used as a coating material to enhance surface properties or protect against wear and tear. However, their implementation as an electronic material has been hindered by inconsistent semiconducting properties arising from their polycrystalline nature and associated processing challenges. In this study, the first demonstration of vertical Schottky barrier diodes fabricated using freestanding PCD membranes (PCDm) is presented, which addresses these limitations by enabling dual‐side access to the PCDm. The Schottky contact is formed on the high‐quality growth surface with larger grains and high sp 3 carbon content, while the ohmic contact is placed on the smoother, sp 2 ‐rich bottom side. This configuration enables distinct contact optimization on each surface, eliminating the trade‐offs encountered in conventional planar devices based on thin‐film PCD. The devices exhibit an excellent rectifying behavior with an on/off ratio of ≈10 3 and a breakdown field of 0.25 MV cm −1 —among the highest reported for PCD‐based Schottky barrier diodes. The result paves the way for the development of high‐performance electronic devices based on freestanding and transferable PCDm, positioning it as a cost‐effective and scalable wide‐bandgap semiconductor for next‐generation electronics.

Tech Support

Original Source

DOI: https://doi.org/10.1002/aelm.202500409