A Broad Photon Energy Range Multi-Strip Imaging Array Based upon Single Crystal Diamond Schottky Photodiode

At a Glance

Metadata	Details
Publication Date	2025-10-28
Journal	Instruments
Authors	C. Verona, M. Angelone, M. Marinelli, G. Verona‐Rinati
Institutions	University of Rome Tor Vergata
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond Multi-Strip Photodiode

Executive Summary

This research details the successful development of a high-performance, single crystal diamond (SCD) multi-strip photodetector designed for 1D imaging across a broad photon energy range (EUV to soft X-rays). The core innovation lies in the material engineering used to achieve stable, high-resolution detection.

SEE Mitigation: The device utilizes a p-type/intrinsic/Schottky metal (PIM) transverse configuration where metallic electrodes are replaced by lithographically patterned Boron-Doped Diamond (BDD) strips. This design effectively suppresses Secondary Electron Emission (SEE), a critical issue for reliable EUV detection.
High Resolution Imaging: The prototype demonstrated excellent spatial resolution, achieving a scanning pixel resolution of 3.2 µm x 2.6 µm when tested with 10 keV soft X-rays.
Material Quality: Fabrication relied on selective homoepitaxial growth via MWPECVD, resulting in a highly uniform intrinsic diamond layer thickness of 1.30 ± 0.05 µm.
Performance Metrics: The detector exhibited high response uniformity across the 32 strips and demonstrated exceptional linearity versus photon flux (r² = 0.9972).
Scalability: The current 1D design (32 strips, 100 µm width, 20 µm gap) is scalable, with future development focused on creating 2D matrix detectors by thinning the HPHT substrate to 20-30 µm and utilizing double-sided deposition.
6CCVD Relevance: This work validates the need for high-precision CVD growth, custom BDD doping, and advanced metalization techniques—all core capabilities offered by 6CCVD.

Technical Specifications

The following hard data points were extracted from the research paper detailing the device structure and performance characteristics.

Parameter	Value	Unit	Context
Detector Configuration	PIM (p-type/Intrinsic/Metal)	N/A	Transverse Schottky Photodiode
Number of Strips	32	N/A	Used for 1D imaging
Strip Width	100	µm	Lithographically patterned BDD
Gap Between Strips	20	µm	Defines spatial resolution
Total Active Area	3.2 x 2.5	mm²	Sensitive region size
Intrinsic Layer Thickness (W)	1.30 ± 0.05	µm	CVD-grown SCD layer
Schottky Contact Material	Platinum (Pt)	N/A	Semitransparent, 10 nm thick
Ohmic Contact Material	Silver (Ag)	N/A	Deposited on p-type diamond strips
Operating Bias (Tested)	0, 1, 4	V	Device operates at zero bias; responsivity increases with bias
SXR Test Energy	10	keV	Used for raster scanning
Scanning Pixel Resolution	3.2 x 2.6	µm	Horizontal (X) x Vertical (Y) resolution
Response Linearity (r²)	0.9972	N/A	Measured vs. He-Ne plasma current
Future Substrate Thickness Goal	20-30	µm	Required for 2D matrix X-ray detection

Key Methodologies

The prototype fabrication relied on precise CVD growth combined with standard microstructuring techniques.

Substrate Preparation: Commercial High-Pressure High-Temperature (HPHT) SCD substrates were used as the base for homoepitaxial growth.
P-type Strip Selective Growth: Boron-Doped Diamond (BDD) microstrip electrodes were selectively grown using Microwave Plasma Enhanced Chemical Vapour Deposition (MWPECVD). A 200 nm thick Chromium (Cr) plasma-resistant coplanar mask, patterned via photolithography, defined the strip geometry.
Intrinsic Layer Deposition: An intrinsic homoepitaxial diamond layer (nominally 1 µm thick) was selectively grown via MWPECVD, burying the BDD strips. This step utilized a patterned Cr layer deposited via the lift-off method.
Surface Conductive Layer Removal: Annealing in air was performed to eliminate the surface conductive layer of the as-grown intrinsic diamond film.
Schottky Contact Formation: A semitransparent Platinum (Pt) electrode (10 nm thick) was thermally evaporated onto the top surface of the intrinsic diamond layer, forming the Schottky junction.
Ohmic Contact Formation: Patterned Silver (Ag) pads were evaporated onto the exposed p-type diamond strips to ensure reliable ohmic contact for signal extraction.
Interconnection: Each of the 32 strips was connected to the readout electronics via micro-wire bonding using 25 µm diameter aluminum wire.

6CCVD Solutions & Capabilities

This research highlights the need for highly specialized CVD diamond materials and advanced microfabrication services. 6CCVD is uniquely positioned to supply the materials and processing required to replicate this 1D detector or advance the design toward the proposed 2D matrix array.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
High-Purity Intrinsic Layer	Optical Grade Single Crystal Diamond (SCD) plates.	We guarantee high-quality, low-defect SCD material, essential for the intrinsic layer to maximize charge collection and maintain low dark current.
Conductive Strip Material	Custom Boron-Doped Diamond (BDD) layers.	We provide precise control over BDD doping levels and thickness (0.1 µm - 500 µm) necessary to create the highly conductive, non-metallic strips that suppress SEE.
Custom Dimensions & Scaling	Custom SCD Plates/Wafers and Advanced Laser Cutting/Patterning.	6CCVD can supply SCD substrates up to 500 µm thick and PCD wafers up to 125 mm in diameter, enabling scaling of the active area beyond the prototype’s 3.2 x 2.5 mm².
Schottky & Ohmic Contacts	In-House Metalization Services (Pt, Ag, Au, Ti, W, Cu).	We offer the precise deposition of the required 10 nm thin, semitransparent Platinum (Pt) Schottky contacts and Silver (Ag) ohmic contacts, ensuring reliable PIM device fabrication.
2D Array Development (Future)	Substrate Thinning and Polishing (SCD thickness 0.1 µm - 500 µm).	To achieve the proposed 2D matrix, the HPHT substrate must be thinned to 20-30 µm. 6CCVD provides state-of-the-art Reactive Ion Etching (RIE) and polishing services, achieving surface roughness (Ra) < 1 nm on SCD, minimizing X-ray attenuation and maximizing device performance.
Engineering Support	In-House PhD Material Science Team.	Our experts specialize in optimizing CVD recipes and material selection for demanding applications like high-resolution X-ray beam monitoring, EUV lithography, and fusion diagnostics, ensuring successful SEE mitigation projects.

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

View Original Abstract

A multi-strip detector made of synthetic single crystal diamond (SCD), based on a p-type/intrinsic diamond/Schottky metal transverse configuration and operating at zero bias voltage, was developed for imaging from extreme UV (EUV) to soft X-rays. The photodetector was patterned with 32 strips made of boron-doped diamond directly deposited, by means of the CVD technique and the standard lithographic technique, on top of the HPHT diamond growth substrate. The width of each strip and the gap between two adjacent strips were 100 μm and 20 μm, respectively. The strips were embedded in intrinsic SCD of an active area of 3.2 × 2.5 mm2, also deposited using the CVD technique in a separate growing machine. In the present structure, the prototype photodetector is suitable for 1D imaging. However, all the dimensions above can be varied depending on the applications. The use of p-type diamond strips represents an attempt to mitigate the photoelectron emission from metal contacts, a non-negligible problem under EUV irradiation. The detector was tested with UV radiation and soft X-rays. To test the photodetector as an imaging device, a headboard (XDAS-DH) and a signal processing board (XDAS-SP) were used as front-end electronics. A standard XDAS software was used to acquire the experimental data. The results of the tests and the detector’s construction process are presented and discussed in the paper.

Tech Support

Original Source

DOI: https://doi.org/10.3390/instruments9040026

References

2013 - A Comprehensive Review of Semiconductor Ultraviolet Photodetectors: From Thin Film to One-Dimensional Nanostructures [Crossref]
2025 - Ultrafast Diamond Photodiodes for vacuum Ultraviolet Imaging in Space-Based Applications [Crossref]
2020 - A single-crystal diamond X-ray pixel detector with embedded graphitic electrodes [Crossref]
2024 - Diamond sensors for hard X-ray energy and position resolving measurements at the European XFEL [Crossref]
2015 - Pixelated transmission-mode diamond X-ray detector [Crossref]
2018 - Diamondpix: A CVD diamond detector with timePix3 chip interface [Crossref]
2022 - Self-powered solar-blind ultrafast UV-C diamond detectors with asymmetric Schottky contacts [Crossref]