Fabrication of UV Photodetector on TiO2/Diamond Film

At a Glance

Metadata	Details
Publication Date	2015-09-24
Journal	Scientific Reports
Authors	Zhangcheng Liu, Fengnan Li, Shuoye Li, Chao Hu, Wei Wang
Institutions	Xi’an Jiaotong University
Citations	104
Analysis	Full AI Review Included

Technical Documentation and Analysis: Fabrication of UV Photodetector on TiO₂/Diamond Film

Executive Summary

This research successfully demonstrates the enhanced performance of an ultraviolet (UV) photodetector utilizing a Titanium Dioxide (TiO₂) film deposited directly onto a high-quality Single Crystal Diamond (SCD) epitaxial layer. The combined structure (TiO₂/Diamond) leverages the wide bandgaps of both materials to create a highly sensitive, selective detector suitable for harsh environments.

Core Achievement: Fabrication of a TiO₂/SCD metal-semiconductor-metal (MSM) UV photodetector showing enhanced responsivity and selectivity compared to traditional diamond-only detectors.
Material Basis: High-quality, unintentionally doped SCD epitaxial film grown via Microwave Plasma Chemical Vapor Deposition (MPCVD) on an HPHT substrate.
Performance: Achieved extremely low dark current (1.12 pA at 30V), indicating high stability and signal-to-noise ratio (SNR).
Selectivity: Demonstrated a superior UV-to-visible rejection ratio of 105 (220 nm vs 400 nm) at 30V bias.
Interface Engineering: The enhanced responsivity and broad spectral response are attributed to the gradient energy band structure formed at the TiO₂/diamond joint film interface.
6CCVD Value Proposition: 6CCVD specializes in providing the foundational high-quality SCD epitaxial material and custom metalization required to replicate and scale this highly desirable wide-bandgap heterostructure device.

Technical Specifications

The following table summarizes the critical material parameters and performance metrics of the fabricated TiO₂/Diamond (Sample A) photodetector.

Parameter	Value	Unit	Context
Diamond Quality (Raman FWHM)	3.9	cm⁻¹	Indicative of high-quality SCD homoepitaxy
SCD Epitaxial Thickness	Approx. 2	µm	Active sensing layer
Substrate Type	Ib-type	N/A	High-Pressure High-Temperature (HPHT)
TiO₂ Film Thickness	450	nm	Deposited via RF Magnetron Sputtering
Electrode Material (Sample A)	Tungsten (W)	N/A	Ohmic contact (100 nm thick)
Electrode Spacing	200	µm	Interdigital spacing for MSM structure
Dark Current (30 V)	1.12	pA	Extremely low leakage current (Sample A)
Peak Responsivity (30 V)	0.2	A/W	Measured at 220 nm (deep UV)
UV-to-Visible Rejection Ratio	105	ratio	220 nm vs 400 nm (at 30 V)
Photo Response Rise Time	20	µs	Under 248 nm KrF Excimer laser pulse
Photo Response Decay Time	1000	µs	Attributed to defects in the TiO₂ layer

Key Methodologies

The successful fabrication relies on precise control over the MPCVD diamond growth process, followed by critical surface preparation and thin-film deposition techniques.

1. SCD Epitaxial Growth (MPCVD)

Substrate: 3 x 3 x 0.3 mm³ Ib-type HPHT diamond.
Thickness: Approx. 2 µm undoped SCD epitaxial layer.
Gas Flow: Total flow rate 500 sccm (H₂ and CH₄).
Methane Concentration: CH₄/(H₂+CH₄) ratio of 0.8%.
Process Pressure: 80 Torr.
Growth Temperature: 850 °C.
Microwave Power: 800 W.

2. Surface Preparation (Oxygen Termination)

Purpose: To change the hydrogen-terminated surface (as-grown) to an oxygen-terminated surface to reduce dark current.
Method: Boiling in acid mixture (H₂SO₄:HNO₃ = 1:1 by volume).
Conditions: 300 °C for 2 hours.

3. TiO₂ Film Deposition

Method: Radio Frequency (RF) Magnetron Sputtering.
Source: 3-inch sintered TiO₂ ceramic target (99.99% purity).
Sputtering Gas: Ar and O₂ mixing atmosphere.
Gas Flow Ratio: Ar:O₂ flow rate ratio set at 2:1 (40 sccm Ar, 20 sccm O₂).
Working Pressure: 1.2 Pa.
Power: 150 W.

4. Electrode Metalization

Material (Sample A): Tungsten (W), 100 nm thick.
Method: RF Magnetron Sputtering (Patterned).
Structure: MSM geometry, 1000 µm width, 200 µm interspace.

6CCVD Solutions & Capabilities

This research validates the use of high-quality MPCVD SCD as the foundational material for advanced wide-bandgap heterojunction photodetectors. 6CCVD is uniquely positioned to supply the required specialized diamond materials and integrated processing services necessary for the next generation of UV sensor development.

Applicable Materials

To replicate or extend the high performance achieved in this paper, researchers require premium, low-defect diamond material with precisely controlled surface chemistry.

Research Requirement	6CCVD Applicable Material	Engineering Rationale
High-Quality Undoped Epi-Layer	Optical Grade Single Crystal Diamond (SCD)	Our SCD offers FWHM < 4 cm⁻¹ and low strain, guaranteeing the high carrier mobility and low defect density necessary for effective charge separation and minimum dark current (1.12 pA).
Surface Control	Custom Terminated SCD Wafers	We deliver SCD wafers with specific termination (e.g., Oxygen-Terminated) crucial for controlling the band alignment and optimizing the interface barrier necessary for the TiO₂ heterojunction.
Need for Visible-Blindness	Intrinsic or Light Boron-Doped SCD	Our intrinsic SCD maintains the wide bandgap (5.5 eV) essential for solar-blind UV detection, yielding superior rejection ratios (up to 10⁵).

Customization Potential

The experimental setup utilized specific dimensions and metal contacts that fall directly within 6CCVD’s expert engineering scope.

Research Specification	6CCVD Custom Capability	Sales Advantage
Custom Dimensions (e.g., 3x3 mm chips)	Custom Laser Cutting & Shaping	We can process SCD and PCD plates up to 125 mm, delivering precise, application-specific dimensions (wafers, plates, chips) ready for further device fabrication.
W/Pd Metalization (W/TiO₂, Pd/Diamond)	Advanced In-House Metalization	We routinely deposit thin films of W and Pd, along with Au, Pt, Ti, and Cu. We manage the entire process, including complex photoresist patterning and lift-off for MSM structures.
Thickness Scaling (2 µm Epi)	Broad Thickness Control	We offer fine control over SCD/PCD thickness ranging from 0.1 µm up to 500 µm, allowing engineers to tune the active volume of the detector layer precisely.

Engineering Support

6CCVD’s in-house PhD team provides specialized consultation to accelerate your research and development efforts in wide-bandgap semiconductor devices.

UV Photodetector Optimization: Our experts can assist with material selection and specification development for projects focused on achieving high-responsivity, high-speed UV detection using complex heterostructures like TiO₂/Diamond.
Interface Engineering: We provide guidance on selecting appropriate metalization schemes (e.g., Ti/Pt/Au versus W/Pd) and surface preparations to optimize Schottky or Ohmic contacts crucial for high-performance MSM device operation.
Scaling and Production: We support the transition from small lab-scale samples (3x3 mm) to inch-size wafers, assisting customers in scaling their UV/Wide Bandgap Device projects for commercial production.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

Tech Support

Original Source

DOI: https://doi.org/10.1038/srep14420