Excess noise in high-current diamond diodes

At a Glance

Metadata	Details
Publication Date	2022-02-07
Journal	Applied Physics Letters
Authors	Subhajit Ghosh, Harshad Surdi, Fariborz Kargar, Franz A. Koeck, Sergey Rumyantsev
Institutions	Institute of High Pressure Physics, Arizona State University
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Analysis: Excess Noise in High-Current Diamond Diodes

This document analyzes the research concerning low-frequency excess noise in diamond diodes, focusing on the implications for high-power electronics reliability assessment. The analysis highlights how 6CCVD’s advanced MPCVD diamond materials and fabrication capabilities directly support the replication, optimization, and scaling of this critical research.

Executive Summary

The following points summarize the key findings and the core value proposition of the research for high-power diamond electronics:

Reliability Assessment: The study validates low-frequency noise spectroscopy as a sensitive, non-destructive technique for assessing material quality and predicting the reliability (Mean-Time-To-Failure, MTTF) of high-power diamond diodes.
Noise Mechanism Identification: Electronic excess noise in the diamond diodes is dominated by Generation-Recombination (G-R) noise, appearing as Lorentzian spectral features, or as 1/f noise in devices with higher defect concentrations (higher turn-on voltage).
Material Structure: Devices utilized a p⁺⁺-i-n layered structure grown on highly Boron-doped (<111>) Single Crystal Diamond (SCD) substrates, incorporating a near-metallic nano-carbon (nanoC) cathode layer.
Current Dependence: The noise spectral density (S_I) exhibits three distinct regions based on forward current (I): scaling as I² at low (I < 10 µA) and high (I > 10 mA) currents, and remaining nearly constant in the intermediate range.
Thermal Stability: Device performance (ideality factor and noise level) was found to be a weak function of temperature, with performance improving as temperature increases, confirming diamond’s suitability for high-power, high-temperature switching applications.
Trap Dynamics: Characteristic trap time constants extracted from G-R noise data show a uniquely strong dependence on current, correlating current jumps in I-V curves with specific trap levels in the bandgap.

Technical Specifications

The following table extracts critical material and performance parameters detailed in the research paper:

Parameter	Value	Unit	Context
Substrate Material	Highly B-doped SCD <111>	N/A	Starting material for p⁺⁺ layer
Substrate Dimensions	3 x 3 x 0.3	mm	Device footprint
p⁺⁺ Doping Concentration (B)	~2 x 10²⁰	/cm³	Highly doped p-type layer
i-layer Thickness	~0.2	µm	Intrinsic layer grown by PECVD
n-layer Thickness	~0.15	µm	Phosphorus-doped layer
n-layer Doping Concentration (P)	~10¹⁸	/cm³	Moderately doped n-layer
Cathode Layer Thickness	~0.1	µm	Highly conductive N-doped nanoC layer
Metal Stack Composition	Ti-Ni-Au	N/A	Anode and Cathode contacts
Metal Stack Thicknesses	50 - 50 - 300	nm	Ti (50 nm) - Ni (50 nm) - Au (300 nm)
Diode Turn-On Voltage (V_T) Groups	~5 V and ~10 V	V	Grouped by low (G-R noise) and high (1/f noise) V_T
Typical Trap Energy Levels	0.2 to 1.7	eV	Defects within the diamond bandgap
Noise Measurement Frequency	10	Hz	Fixed frequency for S_I vs. J analysis

Key Methodologies

The diamond diodes were fabricated using advanced MPCVD techniques and subsequent microfabrication steps:

Substrate Selection: Highly Boron-doped Single Crystal Diamond (SCD) plates with <111> orientation were used as the p⁺⁺ substrate.
i-Layer Growth (PECVD): A ~0.2 µm intrinsic layer was grown using Plasma Enhanced Chemical Vapor Deposition (PECVD) with H₂:CH₄:O₂ precursors at 63 Torr and 1000 W microwave power.
n-Layer Growth (PECVD): A ~0.15 µm Phosphorus-doped n-layer (~10¹⁸/cm³) was grown using H₂:CH₄:TMP precursors at 60 Torr and 2000 W microwave power.
Contact Layer: A ~0.1 µm near-metallic, highly conductive N-doped nano-carbon (nanoC) layer was deposited on the n-layer to minimize cathode contact resistance.
Device Definition: The active area was defined by partial mesa etching the diamond into the i-layer using a SiO₂ hard mask and O₂/SF₆ chemistry in a Reactive Ion Etcher (RIE).
Metalization: Top cathode and bottom anode contacts were formed using UV photolithography and e-beam deposition of a Ti-Ni-Au metal stack (50 nm / 50 nm / 300 nm).
Characterization: Current-voltage (I-V) and low-frequency noise characteristics (S_I) were measured in vacuum using dynamic signal analyzers to extract G-R noise parameters and corner frequencies (f_c).

6CCVD Solutions & Capabilities

This research demonstrates the critical need for high-quality, precisely doped, and structured diamond materials for developing reliable high-power electronics. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond components to replicate, optimize, and scale this technology.

Applicable Materials for High-Power Diode Replication

To replicate the p⁺⁺-i-n structure used in this study, researchers require highly controlled doping and crystal quality.

Boron-Doped Diamond (BDD) Substrates: 6CCVD supplies high-quality, heavily Boron-Doped Diamond (BDD) plates, essential for the p⁺⁺ layer. We can achieve the high doping concentrations (~2 x 10²⁰/cm³) required for low-resistance contacts and device bases.
High-Purity Single Crystal Diamond (SCD): The intrinsic (i) and n-doped layers require high-purity SCD growth. 6CCVD’s MPCVD process minimizes nitrogen and other impurities, reducing the concentration of mid-bandgap traps (0.2 eV to 1.7 eV) that contribute to excess noise and high turn-on voltages.
Polishing Excellence: The study links higher defect concentration to detrimental 1/f noise. 6CCVD guarantees ultra-smooth SCD surfaces (Ra < 1 nm), minimizing surface defects and improving interface quality between the p⁺⁺, i, and n layers, thereby enhancing device reliability.

Customization Potential & Scaling

6CCVD’s core capability is providing custom dimensions and integrated processing steps necessary for advanced device fabrication.

Research Requirement	6CCVD Capability	Benefit to Researcher
Custom Thicknesses	SCD thickness control from 0.1 µm up to 500 µm. Substrates up to 10 mm thick.	Precise replication of the required 0.2 µm (i-layer) and 0.15 µm (n-layer) structures, critical for controlling the Space Charge Limited Conduction (SCLC) regime.
Advanced Metalization	In-house e-beam deposition of custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu.	Direct replication of the required Ti-Ni-Au stack, or optimization using alternative metals (e.g., W, Pt) for improved thermal stability and ohmic contact performance in high-current applications.
Large Area Scaling	Custom plates and wafers up to 125 mm (PCD) and large-area SCD.	Enables the transition from small 3x3 mm research prototypes to commercial-scale high-power diamond switches and power converters.
Doping Flexibility	Ability to supply both Boron-doped (p-type) and Nitrogen/Phosphorus-doped (n-type) layers via custom growth recipes.	Supports complex p-i-n junction designs and the integration of highly conductive nanoC contact layers.

Engineering Support

6CCVD’s in-house PhD team specializes in material science and device physics for diamond electronics. We offer consultation services to assist researchers in material selection for similar Noise Spectroscopy and Reliability Assessment projects. Our expertise ensures that the starting material quality directly supports the goal of minimizing defects and optimizing device performance for high-power switching.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 devices—it scales as I2 at the low (I &lt; 10 μA) 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.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0083383