Vacuum-ultraviolet photodetectors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-11-09 |
| Journal | PhotoniX |
| Authors | Lemin Jia, Wei Zheng, Feng Huang |
| Institutions | Sun Yat-sen University |
| Citations | 190 |
| Analysis | Full AI Review Included |
Technical Documentation: Ultra-Wide Bandgap Semiconductors for VUV Photodetection
Section titled âTechnical Documentation: Ultra-Wide Bandgap Semiconductors for VUV PhotodetectionâCompany: 6CCVD (6ccvd.com) Source Analysis: Jia et al., Photonix (2020) 1:22, âVacuum-ultraviolet photodetectorsâ Focus: Ultra-Wide Bandgap (UWB) Semiconductor Materials (Diamond, AlN, c-BN) for filterless VUV detection (10-200 nm).
Executive Summary
Section titled âExecutive SummaryâThis review confirms that Ultra-Wide Bandgap (UWB) semiconductors, particularly Chemical Vapor Deposition (CVD) diamond, are indispensable for high-performance, filterless Vacuum-Ultraviolet (VUV) photodetectors in demanding applications like space science and high-resolution lithography.
- Core Value Proposition: Diamond offers absolute advantages in VUV selective response, high radiation hardness, low dark current, and superior thermal/chemical stability compared to conventional Si-based detectors.
- Material Requirement: Achieving satisfactory detection performance requires high-quality, low-defect single-crystal diamond (SCD) films, typically grown via Microwave Plasma-Enhanced CVD (MPCVD).
- Performance Benchmarks: Diamond detectors have demonstrated exceptional long-term stability (>98 h under VUV radiation) and high photoresponsivity (up to 21.8 A/W).
- Key Device Structures: Research focuses on three primary mechanisms: Photoconductive (MSM), Photovoltaic (Schottky/PIN), and Avalanche (for high gain/single photon detection).
- Speed and Integration: Recent advances, particularly in heterojunction photovoltaic devices (e.g., Gr/AlN/p-GaN), have achieved ultra-fast response times (rise time 80 ns), paving the way for VUV dynamic imaging arrays.
- 6CCVD Relevance: 6CCVD specializes in the MPCVD growth of the high-quality SCD and Polycrystalline Diamond (PCD) films required to replicate and advance this critical UWB semiconductor research.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| VUV Wavelength Range | 10 - 200 | nm | Spectrum strongly absorbed by oxygen in air. |
| Diamond Bandgap (Eg) | ~5.5 | eV | Corresponds to absorption edge of ~225 nm (UWB). |
| AlN Bandgap (Eg) | ~6.2 | eV | Corresponds to absorption edge of ~200 nm (UWB). |
| c-BN Bandgap (Eg) | ~6.3 | eV | Larger than diamond, potential for < 200 nm detection. |
| Diamond Responsivity (Max) | 21.8 | A/W | All-carbon detector, 218 nm, 50 V bias (Photoconductive). |
| Diamond Stability | >98 | h | Under 10 mW/cm2 VUV radiation (Thin-film detector). |
| AlN Responsivity (Schottky) | 0.325 | A/W | 210 nm, 30 V bias. |
| AlN EQE (Max) | >100 | % | At 60 V bias (indicates internal gain mechanism). |
| AlN Heterojunction Rise Time | 80 | ns | Ultra-fast response to 193 nm nanosecond pulses. |
| AlN Heterojunction Decay Time | 0.4 | ms | Ultra-fast response (improved via thermal enhancement). |
| AlN Avalanche Gain (Max) | 1200 | - | Photocurrent multiplication at -250 V reverse bias. |
| AlN ID Density (Low) | 106 | cm-2 | Required for high-performance MSM photodetectors. |
Key Methodologies
Section titled âKey MethodologiesâThe research reviewed relies heavily on advanced material synthesis and precise device fabrication techniques, primarily focused on achieving ultra-low defect density and controlled doping in UWB films.
- Material Growth (Diamond):
- Microwave Plasma-Enhanced Chemical Vapor Deposition (MPCVD) is the standard technique for growing high-quality intrinsic and doped homoepitaxial Single Crystal Diamond (SCD) films.
- High-Pressure High-Temperature (HPHT) synthetic Ib (100) diamond substrates are commonly used as starting material.
- Material Growth (AlN/c-BN):
- Metal Organic Chemical Vapor Deposition (MOCVD) is used for high-quality AlN epitaxial layers on sapphire or SiC substrates.
- Electron Cyclotron Resonance Microwave Plasma CVD is used for depositing c-BN films, often utilizing diamond intermediate layers for improved adhesion and crystallinity.
- Doping and Conductivity:
- Boron (p-type) and Phosphorus (n-type) doping are used to achieve conductive diamond layers for PIN and Schottky structures.
- Graphene (Gr) is utilized as a transparent, highly conductive window layer in heterojunction photovoltaic devices (e.g., p-Gr/AlN/p-GaN).
- Device Structures:
- Metal-Semiconductor-Metal (MSM): Simple planar structure, often used for materials where doping is difficult (e.g., AlN, h-BN). Requires interdigitated electrodes (IDEs).
- Schottky Barrier Photodiodes: Implemented in both planar (IDT) and vertical (PIM) configurations, requiring precise metal contacts (Al, TiN, Pt).
- Heterojunctions: Used to create built-in electric fields for carrier separation, enabling zero power consumption and ultra-fast response.
- Performance Testing:
- Testing requires harsh conditions: ultra-high vacuum environment and specialized VUV light sources (synchrotron radiation, deuterium lamps, excimer lasers: 193 nm, 157 nm).
- Ultra-fast response dynamics are measured using nanosecond pulses (e.g., 193 nm ArF laser).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights that the performance of UWB VUV photodetectors is fundamentally limited by the quality, purity, and structural uniformity of the semiconductor material. 6CCVD is uniquely positioned to supply the necessary high-specification diamond materials and custom fabrication services required to advance this field.
Applicable Materials for VUV Detector Research
Section titled âApplicable Materials for VUV Detector ResearchâThe most critical requirement identified in the paper is the need for high-quality, low-defect SCD films grown by MPCVD, which is 6CCVDâs core expertise.
| 6CCVD Material | Application Relevance | Key Specification Match |
|---|---|---|
| Optical Grade SCD | Active layer for Photoconductive, Photovoltaic, and Avalanche detectors. Essential for high radiation hardness and low dark current. | SCD thickness up to 500 ”m; Ra < 1 nm polishing for optimal surface quality. |
| Boron-Doped Diamond (BDD) | Required for p-type layers in PIN and Schottky barrier structures (e.g., p-type/intrinsic/metal (PIM) devices). | Custom doping concentrations available for controlled conductivity and junction formation. |
| High-Purity PCD | Suitable for large-area MSM detectors and applications requiring high thermal stability where SCD cost is prohibitive. | Plates/wafers up to 125 mm diameter; Polishing Ra < 5 nm for inch-size wafers. |
Customization Potential for Device Fabrication
Section titled âCustomization Potential for Device FabricationâThe development of integrated VUV photodetector arrays (e.g., 200 ”m x 5 ”m units) and specialized electrode geometries (MSM interdigitated fingers) necessitates precise customization, which 6CCVD provides in-house.
- Custom Dimensions and Substrates: 6CCVD provides SCD and PCD plates/wafers up to 125 mm in diameter, accommodating the need for large-area detectors and integrated arrays. Custom thicknesses (0.1 ”m to 500 ”m) allow optimization of the depletion layer thickness for maximum quantum efficiency and frequency response.
- Advanced Metalization Services: The paper details the use of various metal stacks (Al, Pt, TiN, Au, Ni/Mo/Au) for ohmic and Schottky contacts. 6CCVD offers internal metalization capabilities, including:
- Schottky Contacts: Deposition of Au, Pt, Pd.
- Ohmic Contacts: Deposition of Ti, W, Cu, or custom stacks (e.g., Ti/Pt/Au) required for specific UWB materials.
- Precision Structuring: 6CCVD can provide laser cutting and patterning services to define the precise interdigitated electrode (IDE) spacing (e.g., 2 ”m width, 5 ”m spacing) and device geometries required for MSM and IDT-PIM structures.
Engineering Support
Section titled âEngineering SupportâThe trade-off between photoresponsivity (gain) and response time (carrier lifetime) is a critical challenge in VUV detector design. This optimization requires deep expertise in material science and device physics.
- Defect Control: 6CCVDâs in-house PhD team specializes in controlling defect density and surface states in MPCVD diamond, which is essential for minimizing persistent photoconductivity and achieving the fast response speeds (ns range) needed for ultra-fast VUV dynamic imaging projects.
- Vertical vs. Planar Design: We offer consultation on material selection and structure optimization (e.g., vertical PIM vs. planar IDT-PIM) to maximize short-wavelength response, as demonstrated in the reviewed research.
- Radiation Hardness: Our SCD materials are inherently suited for harsh environments (space exploration, synchrotron radiation monitoring) due to their superior radiation tolerance, a key figure of merit for VUV space instruments like LYRA.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract High-performance vacuum-ultraviolet (VUV) photodetectors are of great significance to space science, radiation monitoring, electronic industry and basic science. Due to the absolute advantages in VUV selective response and radiation resistance, ultra-wide bandgap semiconductors such as diamond, BN and AlN attract wide interest from researchers, and thus the researches on VUV photodetectors based on these emerging semiconductor materials have made considerable progress in the past 20 years. This paper takes ultra-wide bandgap semiconductor filterless VUV photodetectors with different working mechanisms as the object and gives a systematic review in the aspects of figures of merit, performance evaluation methods and research progress. These miniaturized and easily-integrated photodetectors with low power consumption are expected to achieve efficient VUV dynamic imaging and single photon detection in the future.