Negative Differential Resistance of n-ZnO Nanorods/p-degenerated Diamond Heterojunction at High Temperatures
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-07-15 |
| Journal | Frontiers in Chemistry |
| Authors | Dandan Sang, Jiaoli Liu, Xiaofeng Wang, Dong Zhang, Feng Ke |
| Institutions | Jilin University, Shandong University of Technology |
| Citations | 18 |
| Analysis | Full AI Review Included |
Negative Differential Resistance of n-ZnO Nanorods/p-degenerated Diamond Heterojunction at High Temperatures
Section titled âNegative Differential Resistance of n-ZnO Nanorods/p-degenerated Diamond Heterojunction at High TemperaturesâExecutive Summary
Section titled âExecutive SummaryâThis study successfully fabricated and characterized an n-ZnO Nanorods (NRs)/p-degenerated diamond tunneling diode designed for high-temperature operation, focusing on Negative Differential Resistance (NDR) properties.
- Core Achievement: Stable NDR phenomena were observed in the heterojunction at 20 °C and 80 °C, confirming its suitability for high-temperature electronic applications.
- Material Basis: The device utilizes heavily boron-doped (p-degenerated) diamond (carrier density 1.7 x 1020 cm-3) combined with n-type ZnO NRs.
- Performance Trend: Increasing temperature from 20 °C to 80 °C resulted in a significant increase in forward current (Ip increased by >7 times) and a reduction in the turn-on voltage (from 1.5 V to 0.7 V).
- NDR Strength: The Peak-to-Valley Current Ratio (PVCR) decreased from 1.7 at 20 °C to 1.1 at 80 °C, indicating a weakening of the NDR effect as thermal processes become more dominant.
- Tunneling Mechanism: At lower temperatures (20 °C and 80 °C), carrier transport is dominated by tunneling from the diamond valence band into the deep level defect band (oxygen vacancies) of the ZnO NRs.
- Failure Mode: At 120 °C, the NDR effect completely disappeared, and the device transitioned into a standard non-degenerate p-n heterojunction, dominated by enhanced thermionic emission and diffusion current.
- Conduction Models: High-voltage conduction adhered to Fowler-Nordheim (FN) tunneling theory, while low-voltage conduction followed direct tunneling.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Peak Current (Ip) | 2.6 | ”A | 20 °C, Forward Bias |
| Peak Current (Ip) | 20.4 | ”A | 80 °C, Forward Bias |
| Valley Current (Iv) | 1.5 | ”A | 20 °C, Forward Bias |
| Valley Current (Iv) | 19.3 | ”A | 80 °C, Forward Bias |
| PVCR | 1.7 | Dimensionless | 20 °C (Maximum NDR observed) |
| PVCR | 1.1 | Dimensionless | 80 °C (NDR weakened) |
| Turn-on Voltage (Vturn-on) | 1.5 | V | 20 °C |
| Turn-on Voltage (Vturn-on) | 0.7 | V | 80 °C (Reduced due to thermal effects) |
| P-Diamond Carrier Density | 1.7 x 1020 | cm-3 | Measured by Hall effect (Degenerated structure) |
| P-Diamond Resistivity | 102 | Ω cm2 | Measured by Hall effect |
| P-Diamond Mobility | 11 | cm2 V-1 s-1 | Measured by Hall effect |
| ZnO NR Average Length | ~2 | ”m | Structural analysis |
| ZnO NR Average Diameter | ~80 | nm | Structural analysis |
| Diamond Film Thickness | 4 | ”m | HFCVD growth result |
| NDR Disappearance Temperature | 120 | °C | Transition to rectification characteristics |
Key Methodologies
Section titled âKey MethodologiesâThe heterojunction device was fabricated using a two-step synthesis process involving Hot Filament Chemical Vapor Deposition (HFCVD) for the diamond layer and thermal evaporation for the ZnO NRs.
1. P-Degenerated Diamond Film Synthesis
Section titled â1. P-Degenerated Diamond Film Synthesisâ- Method: 150 V bias-assisted Hot Filament Chemical Vapor Deposition (HFCVD).
- Substrate: Silicon wafers (1 cm x 1 cm), pre-abraded with diamond paste for nucleation enhancement.
- Filament: Spiral tantalum wire, heated to approximately 2,000 °C.
- Growth Temperature: Substrate temperature maintained at ~700-800 °C.
- Pressure: Total pressure set at 40 Torr.
- Gas Flow: Methane (CH4)/Hydrogen (H2) flow rate ratio of 2.6/200 sccm.
- Doping: Boron source was liquid B(OCH3)3, incorporated via H2 gas bubbling at a flow rate of 20 sccm.
- Result: Diamond films displayed a thickness of 4 ”m after 4 hours of deposition.
2. N-ZnO Nanorods (NRs) Fabrication
Section titled â2. N-ZnO Nanorods (NRs) Fabricationâ- Method: Thermal evaporation in a horizontal tube furnace.
- Source Material: Mixed raw powders of ZnO and Aluminum (Al).
- Source Temperature: Heated in the quartz tube at 850 °C.
- Substrate Placement: P-degenerated diamond substrates were placed downstream from the source.
- Substrate Temperature: Maintained at approximately 500 °C.
- Pressure: Constant pressure of 6 x 104 Pa.
3. Device Assembly and Characterization
Section titled â3. Device Assembly and Characterizationâ- Device Structure: Tunneling diode heterojunction.
- Negative Electrode: Transparent conductive Indium-Tin-Oxide (ITO) glass pressed onto the ZnO NRs.
- Positive Electrode: Silver (Ag) wire employed on the p-degenerated diamond.
- Structural Analysis: SEM, TEM, Raman spectroscopy (514.5 nm Ar+ ion laser), and X-ray diffraction (XRD) were used to confirm morphology and crystal structure.
- Electrical Testing: Temperature-dependent I-V characteristics were measured using a Keithley Series 2400 SourceMeter Instruments.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful demonstration of stable NDR in a diamond-based heterojunction at elevated temperatures opens pathways for specialized electronic components in demanding environments.
- High-Temperature Electronics: Ideal for devices requiring stable operation in high-power modules, aerospace, automotive engine control units, or deep-well drilling equipment where ambient temperatures exceed 100 °C.
- Resonant Tunneling Diodes (RTDs): The NDR effect is crucial for RTDs, enabling ultra-high-frequency (GHz to THz) oscillators, mixers, and detectors used in advanced communication systems.
- High-Density Logic and Memory: NDR devices can be used to construct multi-valued logic circuits, potentially simplifying complex logic gates and increasing data density in specialized memory architectures (Resistive Switching).
- High-Power Switching: Diamondâs superior thermal conductivity (greater than silicon or GaAs) makes this heterojunction suitable for high-power switching applications, minimizing heat dissipation issues.
- Optoelectronic Devices: Utilizing the wide bandgap properties of both ZnO and diamond for robust UV photodetectors and emitters operating in harsh, high-radiation environments.
View Original Abstract
In the present study, an n-ZnO nanorods (NRs)/p-degenerated diamond tunneling diode was investigated with regards to its temperature-dependent negative differential resistance (NDR) properties and carrier tunneling injection behaviors. The fabricated heterojunction demonstrated NDR phenomena at 20 and 80°C. However, these effects disappeared followed by the occurrence of rectification characteristics at 120°C. At higher temperatures, the forward current was increased, and the turn-on voltage and peak-to-valley current ratio (PVCR) were reduced. In addition, the underlying mechanisms of carrier tunneling conduction at different temperature and bias voltages were analyzed through schematic energy band diagrams and semiconductor theoretical models. High-temperature NDR properties of the n-ZnO NRs/p-degenerated diamond heterojunction can extend the applications of resistive switching and resonant tunneling diodes, especially in high-temperature, and high-power environments.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2018 - Facile fabrication of self-assembled ZnO nanowire network channels and its gatecontrolled UV detection [Crossref]
- 2011 - Resistive switching characteristics of maghemite nanoparticle assembly. J [Crossref]
- 2007 - Room temperature observation of negative differential resistance effect using ZnO nanocrystal structure with double Schottky barriers [Crossref]
- 2015 - Observation of room temperature negative differential resistance in solution synthesized ZnO nanorod [Crossref]
- 2007 - Physics of Semiconductor Devices
- 2017 - High-sensitive Ultraviolet photodetectors based on ZnO Nanorods/CdS heterostructures [Crossref]
- 2006 - Boron spectral density and disorder broadening in B-doped diamond [Crossref]
- 2013 - Epitaxial growth of ZnO nanorods on diamond and negative differential resistance of n-ZnO nanorod/p-diamond heterojunction [Crossref]
- 2010 - Investigation on crystalline structure, boron distribution, and residual stresses in freestanding boron-doped CVD diamond films [Crossref]
- 2018 - Temperature dependent negative differential resistance behavior in multiferroic metal organic framework (CH3)2NH2Mn(HCOO)3 crystals [Crossref]