Excess noise in high-current diamond diodes
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2022-02-07 |
| Journal | Applied Physics Letters |
| Authors | Subhajit Ghosh, Harshad Surdi, Fariborz Kargar, Franz A. Koeck, Sergey Rumyantsev |
| Institutions | Polish Academy of Sciences, Arizona State University |
| Citations | 21 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis study investigates low-frequency excess noise in high-current diamond p++-i-n diodes to establish a baseline for noise spectroscopy-based reliability assessment in high-power diamond electronics.
- Noise Mechanism Identification: The electronic excess noise is dominated by generation-recombination (G-R) noise, appearing as Lorentzian features, or 1/f noise, depending on the device quality (turn-on voltage).
- Defect Correlation: G-R noise is characteristic of diodes with lower turn-on voltages (fewer defects), while 1/f noise dominates in high turn-on voltage diodes (higher trap concentration).
- Unique Current Dependence: The noise spectral density (SI) exhibits three distinct regions: scaling as I2 at low (<10 ĀµA) and high (>10 mA) currents, but remaining nearly constant in the intermediate current density range (0.1 to 100 A/cm2).
- Trap Time Constants: Characteristic trap time constants, extracted from G-R noise data, show a uniquely strong dependence on current (fc ~ JĪ²), attributed to the deep, partially ionized donor/acceptor states and hole-dominated transport.
- Thermal Performance: Diode performance improves with increasing temperature; the ideality factor (n) decreases, and the noise level remains almost constant, which is highly beneficial for high-power switching applications.
- Reliability Tool Development: The large variation in noise levels (spanning three orders of magnitude at low currents) between different diodes confirms the potential of noise spectroscopy as a sensitive, non-destructive predictor for diamond diode lifetime (Mean-Time-To-Failure, MTTF).
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | p-type <111> HPHT diamond | N/A | Highly B-doped (p++) |
| Substrate Doping (B) | ~2 x 1020 | cm-3 | p++ layer |
| i-layer Thickness | ~0.2 | Āµm | Intrinsic layer |
| n-layer Thickness | ~0.15 | Āµm | Moderately P-doped layer |
| n-layer Doping (P) | ~1018 | cm-3 | P-doped layer |
| NanoC Layer Thickness | ~0.1 | Āµm | N-doped, near-metallic cathode contact |
| Low Turn-on Voltage (VT) | ~5 | V | Devices showing G-R noise |
| High Turn-on Voltage (VT) | ~10 or higher | V | Devices showing 1/f noise |
| Typical Trap Energy Range | 0.2 to 1.7 | eV | Defects in diamond bandgap |
| P Dopant Activation Energy | 0.43 to 0.63 | eV | In the n-layer |
| Low Current Noise Scaling | SI ~ I2 | N/A | Current I < 10 ĀµA |
| High Current Noise Scaling | SI ~ I2 | N/A | Current I > 10 mA |
| Intermediate Current Density | 0.1 to 100 | A/cm2 | SI is nearly constant |
| Corner Frequency Exponent (Ī²) | 0.31, 1.15, 1.39, 1.35 | N/A | fc ~ JĪ² for devices 1, 2, 3 |
| Measurement Temperature Range | 296 to 400 | K | Elevated temperature testing |
| Fixed Noise Frequency (f) | 10 | Hz | Used for SI vs J plots |
Key Methodologies
Section titled āKey MethodologiesāThe diamond diodes utilized a p++-i-n structure grown on a highly B-doped <111> single crystal diamond plate.
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Material Growth (PECVD):
- i-layer Growth: Plasma Enhanced Chemical Vapor Deposition (PECVD) using H2:CH4:O2 mixture.
- Chamber Pressure: 63 Torr.
- Microwave Power: 1000 W.
- n-layer Growth: PECVD using H2:CH4:TMP mixture.
- Chamber Pressure: 60 Torr.
- Microwave Power: 2000 W.
- Cathode Contact Layer: A near-metallic highly conductive N-doped nano-carbon (nanoC) layer was grown on the n-layer to reduce contact resistance.
- i-layer Growth: Plasma Enhanced Chemical Vapor Deposition (PECVD) using H2:CH4:O2 mixture.
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Device Fabrication:
- Active Area Definition: Defined by partially mesa etching the diamond into the i-layer.
- Hard Mask: SiO2 hard mask.
- Etching Chemistry: O2/SF6 chemistry in a Reactive Ion Etcher (RIE).
- Contact Definition: UV photolithography and e-beam deposition.
- Metal Stack (Cathode/Anode): Ti-Ni-Au metal stack with thicknesses of 50 nm - 50 nm - 300 nm.
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Electrical and Noise Characterization:
- I-V and Noise Measurement: Conducted in vacuum using an Agilent/Lake Shore setup.
- Noise Spectra Acquisition: Acquired using a dynamic signal analyzer (Stanford Research).
- Noise Analysis: Low-frequency excess noise (SI) was analyzed as a superposition of 1/f noise and G-R noise (Lorentzian features).
- Trap Time Constant Extraction: G-R noise was fitted using the Lorentzian expression SI(f) = S0/[1 + (2ĻfĻ)2] to determine the characteristic corner frequency (fc = 1/(2ĻĻ)).
Commercial Applications
Section titled āCommercial ApplicationsāThe research focuses on developing reliable, high-performance diamond devices, leveraging diamondās superior material properties for demanding electrical applications.
- High-Power Electronics and Switches: Diamond diodes are targeted specifically for high-current switching applications where high critical electric field and thermal conductivity are essential.
- Electricity Grid Infrastructure: Applications in power converters and inverters requiring highly reliable, ultra-wide bandgap (UWBG) semiconductors to meet increasing efficiency demands.
- Device Reliability Assessment: Implementation of noise spectroscopy as a non-destructive, short-time measurement technique to predict device Mean-Time-To-Failure (MTTF) and assess material quality.
- High-Temperature Operation: Utilization of diamondās weak dependence of current and noise on temperature, allowing for stable and improved performance in high-temperature operating environments (up to 400 K tested).
- Advanced Semiconductor Manufacturing: Providing a noise-level baseline necessary for optimizing diamond Chemical Vapor Deposition (CVD) growth and processing techniques by correlating noise signatures (G-R vs. 1/f) with defect concentrations.
View Original Abstract
We report the results of an investigation of low-frequency excess noise in high-current diamond diodes. It was found that the electronic excess noise of the diamond diodes is dominated by the 1/f and generation-recombination noise, which reveals itself as Lorentzian spectral features (f is the frequency). The generation-recombination bulges are characteristic of diamond diodes with lower turn-on voltages. The noise spectral density dependence on forward current, I, reveals three distinctive regions in all examined devicesāit scales as I2 at the low (I &lt; 10 Ī¼A) and high (I &gt; 10 mA) currents and, rather unusually, remains nearly constant at the intermediate current range. The characteristic trap time constants, extracted from the noise data, show a uniquely strong dependence on current. Interestingly, the performance of the diamond diodes improves with the increasing temperature. The obtained results are important for the development of noise spectroscopy-based approaches for device reliability assessment for high-power diamond electronics.