Minority carrier lifetime in ultrananocrystalline diamond/hydrogenated amorphous carbon composite films
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-01-01 |
| Journal | Transactions of the Materials Research Society of Japan |
| Authors | Naofumi Nishikawa, Satoshi Takeichi, Takanori Hanada, Shuya Tategami, Atsuhiko Fukuyama |
| Institutions | Kyushu University, University of Miyazaki |
| Citations | 3 |
| Analysis | Full AI Review Included |
Technical Analysis and Commercial Documentation: Minority Carrier Lifetime in UNCD/a-C:H Films
Section titled âTechnical Analysis and Commercial Documentation: Minority Carrier Lifetime in UNCD/a-C:H FilmsâExecutive Summary
Section titled âExecutive SummaryâThis research investigates the critical impact of hydrogenation on the minority carrier lifetime ($\tau$) and resulting photovoltaic performance of p-type Ultrananocrystalline Diamond/hydrogenated Amorphous Carbon (UNCD/a-C:H) composite films, targeting UV sensor applications.
- Core Achievement: Successful experimental measurement of minority carrier lifetime ($\tau$) in UNCD/a-C:H films using microwave reflected photoconductivity decay (”-PCD).
- Lifetime Enhancement: Hydrogenated films (UNCD/a-C:H) exhibited a 105% improvement in minority carrier lifetime ($\tau_{SRH}$) (0.43 ”s) compared to non-hydrogenated films (UNCD/a-C) (0.21 ”s).
- Defect Management: The observed lifetime increase is directly attributed to the termination of dangling bonds by hydrogen atoms, effectively passivating deep trap centers that cause rapid carrier recombination.
- Photovoltaic Performance: pn heterojunction diodes (p-type UNCD/a-C:H / n-type Si) showed that photo-induced current increases proportionally with enhanced hydrogenation content in the diamond layer.
- Application Relevance: Confirms that defect control in the diamond film layer is paramount for optimizing photodetection performance, validating diamond films as viable semiconductors for UV photovoltaics.
- Methodology: Films were deposited via Coaxial Arc Plasma Deposition (CAPD), with hydrogen content controlled by varying the arc discharge voltage during growth.
Technical Specifications
Section titled âTechnical SpecificationsâThe following quantitative data points were extracted from the analysis of the UNCD/a-C:H films and fabricated heterojunction diodes:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minority Carrier Lifetime ($\tau_{SRH}$) (Hydrogenated) | 0.43 | ”s | SRH recombination time constant (p-UNCD/a-C:H) |
| Minority Carrier Lifetime ($\tau_{SRH}$) (Non-Hydrogenated) | 0.21 | ”s | SRH recombination time constant (p-UNCD/a-C) |
| Fastest Decay Component ($\tau_{Auger}$) (Hydrogenated) | 0.07 | ”s | Auger recombination time constant |
| Slowest Decay Component ($\tau_{SRH-trapping}$) (Hydrogenated) | 5.16 | ”s | SRH recombination with carrier-trapping effects |
| Diode Film Doping (p-type) | 0.5 | at.% | Boron concentration |
| Lifetime Test Substrate Resistivity | > 10 | kΩ·cm | Insulating Single-Crystalline Si |
| Diode Substrate Resistivity / Thickness | 1-5 / 260 | Ω·cm / ”m | n-type Si (100) substrate |
| Photodetection Test Wavelength | 254 | nm | UV illumination source (Monochromatic lamp) |
| ”-PCD Excitation Wavelength / Pulse | 349 / 5 | nm / ns | Laser pulse for carrier generation |
| Diode Ideality Factor Range | 2 to 3 | - | Indicates dominant tunneling and G-R processes |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully related diamond film growth parameters to resulting electronic properties, focusing on defect control via hydrogenation.
- Film Deposition: UNCD/a-C:H films were grown using Coaxial Arc Plasma Deposition (CAPD) on insulating Si substrates, contrasting with 6CCVDâs superior Microwave Plasma Chemical Vapor Deposition (MPCVD).
- Substrate Conditions:
- Substrate Temperature: 550 °C.
- Gas Pressure: Hydrogen (H2) pressure maintained at 53.3 Pa.
- Base Pressure: Less than 10-4 Pa.
- Hydrogen Content Control (Recipe Variation): Hydrogen content in the UNCD/a-C:H film was qualitatively controlled by varying the arc plasma discharge voltage (70 V, 85 V, 100 V, 115 V). Lower voltage resulted in decreased carbon species ejection and thus higher effective hydrogen content in the resulting film.
- Doping: P-type conduction was achieved via in-situ boron doping (0.5 at.%) during the deposition process for heterojunction diode fabrication.
- Heterojunction Fabrication:
- Structure: p-type UNCD/a-C:H film deposited on an n-type Si (100) substrate.
- Electrodes: Palladium (Pd) and Aluminum (Al) electrodes were applied via RF magnetron sputtering onto the top (p-type layer) and back (n-type Si), respectively.
- Lifetime Measurement: Minority carrier lifetime ($\tau$) was determined by analyzing the excess carrier ($\Delta n$) recombination kinetics using the Microwave Reflected Photoconductivity Decay (”-PCD) method.
6CCVD Solutions & Capabilities: Engineering Semiconductor Diamond for Advanced Photovoltaics
Section titled â6CCVD Solutions & Capabilities: Engineering Semiconductor Diamond for Advanced Photovoltaicsâ6CCVD is positioned as the ideal partner to replicate, optimize, and scale this research through our specialization in high-purity, defect-controlled MPCVD diamond materials and advanced fabrication services. The successful management of trap centers via hydrogenation in this study underscores the critical importance of material purity and defect passivationâareas where 6CCVDâs MPCVD methods excel over arc deposition techniques.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve and surpass the performance metrics demonstrated in this research, 6CCVD offers the following materials:
- Boron-Doped Single Crystal Diamond (BDD-SCD): For high-performance UV photodiodes requiring the longest possible minority carrier lifetimes and highest mobility. SCD minimizes grain boundaries entirely, providing a far more controlled material than UNCD/a-C:H.
- Heavy Boron-Doped Polycrystalline Diamond (BDD-PCD): Suitable for large-area UV sensors or high-current electrochemical electrodes. 6CCVD offers high-quality PCD up to 125 mm diameter, allowing for significant scaling of photovoltaic arrays.
- Optical Grade SCD: For applications requiring UV transparency and minimal internal defects, ensuring maximum photon absorption in the diamond layer.
Customization Potential & Engineering Advantages
Section titled âCustomization Potential & Engineering Advantagesâ| Paper Requirement / Challenge | 6CCVD Customization & Advantage |
|---|---|
| Material Deposition Method | Superior MPCVD Growth: Unlike the CAPD method used in the study, 6CCVD employs high-purity MPCVD, providing precise control over gas mixtures (including H2 content) and temperature, yielding films with superior structural homogeneity and inherently fewer defects than UNCD films. |
| P-type Doping Control | Precision BDD Layers: We provide custom, graded, or uniformly doped boron films (SCD or PCD) to exact resistivity specifications needed for pn or Schottky junction design, optimizing for carrier injection and transport. |
| Heterojunction Metalization | In-House Electrode Fabrication: The study required custom Pd/Al sputtering. 6CCVD offers full, turnkey metalization services including Au, Pt, Pd, Ti, W, and Cu layers, ensuring stable, low-resistance ohmic contacts essential for robust diode performance. |
| Substrate Compatibility | Flexible Growth on Diverse Substrates: 6CCVDâs MPCVD system is capable of growing high-quality diamond films on Si (as used in the paper), as well as on SiC, Sapphire, and various custom insulating substrates, meeting specific device integration needs. |
| Surface Finish & Defect Density | Ultra-Low Roughness Polishing: Defect control is critical for carrier lifetime. 6CCVD guarantees ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, significantly reducing surface recombination centers. |
Engineering Support
Section titled âEngineering SupportâThe research successfully demonstrated that defect management is key to unlocking the full potential of diamond semiconductors in photovoltaic applications. 6CCVDâs in-house PhD team can assist engineers and scientists with material selection, precise gas phase chemistry control (including specific H2 incorporation during MPCVD), and doping profiles necessary to optimize carrier lifetime for similar UV Photovoltaic Sensor or High-Temperature Diode projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) is provided for all specialized diamond products.
View Original Abstract
Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films possess the following specific characteristics: (a) the appearance of additional energy levels in diamond bandgap and (b) large absorption coefficients ranging from visible to ultraviolet, both of which might be due to large number of grain boundaries between UNCD grains and those between UNCD grains and a-C:H. Owing to them, UNCD/a-C:H films are expected to be applied to photovoltaics such as UV sensors. Actually thus far, we have fabricated pn heterojunction diodes comprising p-type UNCD/a-C:H films and n-type Si substrates, and confirmed their photovoltaic action. In this study, the minority carrier lifetime, which is an important factor for photovoltaics, was experimentally measured by microwave reflected photoconductivity decay, and it was estimated to be 0.21 and 0.43 ÎŒs for UNCD/a-C and UNCD/ a-C:H, respectively. In addition, on the basis of the previous work on the heterojunctions, the effects of hydrogenation on the photovoltaic action of the heterojunctions were studied. The photocurrent apparently increases with an enhancement in the hydrogenation of UNCD/a-C:H films, which might be because dangling bonds in the UNCD/a-C:H films, which act as photogenerated-carrier trap centers, are terminated by hydrogen atoms.