Computationally assessing diamond as an ultrafast pulse shaper for high-power ultrawideband radar

At a Glance

Metadata	Details
Publication Date	2023-08-24
Journal	Frontiers in Carbon
Authors	Christopher S. Herrmann, Joseph Croman, Sergey V. Baryshev
Institutions	Michigan State University, United States Naval Research Laboratory
Citations	1
Analysis	Full AI Review Included

Diamond MPCVD Solutions for Ultrafast High-Power Switching

Executive Summary

This technical analysis, based on the computational assessment of diamond Diode Avalanche Shapers (DAS), confirms Single Crystal Diamond (SCD) as the superior material for next-generation high-power, ultrafast electronics, specifically targeting Ultrawideband (UWB) radar applications.

Breakthrough Performance: Diamond DAS devices are computationally shown to achieve sub-50 ps switching times (38 ps FWHM) and deliver peak output voltage rates up to 1 kV/ps.
High Power Density: The simulated device generates 2.1 kV output voltage and 0.5 MW peak power, significantly outperforming comparable Si devices by orders of magnitude.
Material Supremacy: Diamond’s exceptional material properties—specifically its high breakdown field (10 MV/cm) and high streamer velocity ($\ge 10^8$ cm/s)—enable a Johnson’s Figure of Merit (JFOM) 100 times greater than Silicon (200 V/ps vs. 2 V/ps).
UWB Radar Advancement: This technology is critical for producing the ~10 ps pulses required for 30 GHz and above UWB vehicular radar, enabling cm-range resolution over kilometers.
6CCVD Material Requirement: Replication and extension of this research necessitate high-purity, low-defect Single Crystal Diamond (SCD) substrates and precise epitaxial growth for the p-i-n structure.
Customization Focus: 6CCVD offers the required high-quality SCD materials, custom thickness control (down to 10 µm i-layer), and specialized metalization for realizing these advanced p-i-n diode structures.

Technical Specifications

The following table summarizes the critical material properties and the simulated performance metrics of the Diamond DAS compared to Silicon (Si) and Silicon Carbide (4H-SiC).

Parameter	Diamond Value	Unit	Context / Comparison
Johnson’s Figure of Merit (JFOM)	200	V/ps	100x higher than Si (2 V/ps); 2x higher than 4H-SiC (90 V/ps).
Breakdown Field ($E_{br}$)	10	MV/cm	Highest known semiconductor breakdown field.
Bandgap ($E_g$)	5.47	eV	Wide bandgap material, essential for high-power operation.
Electron Mobility ($\mu_e$)	4500	cm²/V-s	High mobility supports fast carrier transport.
Electron Saturation Velocity ($v_s$)	2 x 10⁷	cm/s	Saturated drift velocity.
Streamer Velocity ($v_p$)	$\ge 10^8$	cm/s	Enables ultrafast switching, 10-100x faster than $v_s$.
Simulated Switching Time (FWHM)	38	ps	Achieved for 10 µm i-layer device.
Peak Output Voltage Rate (dV/dt)	1	kV/ps	Achieved with 0.1 kV/ps input ramp rate (ultimate performance).
Peak Output Voltage	2.1	kV	Delivered by a single 1 mm² device.
Peak Output Power	0.5	MW	High-power capability for UWB radar.
i-Layer Thickness ($L_i$)	10	µm	Thin base required for sub-nanosecond switching.
Device Cross-Sectional Area	1	mm²	Standard size used in simulation.

Key Methodologies

The research utilized Technology Computer-Aided Design (TCAD) to simulate the transient behavior of the diamond DAS, focusing on the physics of avalanche breakdown and streamer formation.

Simulation Environment: Synopsys Sentaurus TCAD software was used for 3D mixed-mode simulation (combining device physics and circuit SPICE-like analysis).
Physical Model: The drift-diffusion approach was employed, incorporating constant carrier mobility, velocity saturation at high fields, and avalanche dynamics based on the Van Overstraeten de-Man model.
Device Structure: A canonical vertical p-i-n diode structure was simulated.
- i-Layer: Undoped/low-doped layer (10 µm thickness) where the streamer forms.
- Doping: Light p-doping (Boron) in the i-layer and heavy n⁺/p⁺ doping in the contact layers (10¹⁹ cm^-3).
Input Pulse Generation: A hypothetical DSRD-based voltage source provided the input pulse, characterized by:
- Peak Voltage: 3 kV.
- Rise Time: 1.5 ns (linear ramp).
- Ramp Rate (dV/dt): Varied from 1 V/ps up to 100 V/ps to test ultimate performance limits.
Circuit Configuration: The DAS was connected to a virtual circuit (Figure 1), including a 50 Ω load resistor ($R_L$) and a DC pre-bias voltage ($V_{ref}$) set at 10 V to tune the breakdown point.
Performance Metric: The primary figure of merit assessed was the peak output voltage rate (dV/dt) and the resulting switching time (FWHM of dV/dt).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials necessary to transition this computational breakthrough into realized, high-performance devices. Our capabilities directly address the stringent material and structural requirements of the diamond DAS.

Applicable Materials

To replicate and extend this high-power switching research, 6CCVD recommends the following materials:

Single Crystal Diamond (SCD) Substrates: Required for homoepitaxial growth of the p-i-n structure. Our SCD material offers the high purity and low defect density essential for achieving the theoretical 10 MV/cm breakdown field and high carrier mobility.
Boron-Doped Diamond (BDD) Epitaxy: Necessary for the p⁺ contact layer and for controlled p-doping of the intrinsic (i) layer, as simulated in the paper. 6CCVD provides precise control over Boron concentration and thickness for optimal conductivity.
Custom Epitaxial Thickness: The simulated device requires an extremely thin i-layer (10 µm). 6CCVD specializes in growing SCD layers with thickness control ranging from 0.1 µm up to 500 µm, ensuring the precise geometry needed for ultrafast switching.

Customization Potential

The realization of the diamond DAS requires specific dimensions, doping profiles, and contact layers, all of which are core 6CCVD capabilities:

Device Requirement (from Paper)	6CCVD Custom Capability	Technical Advantage
Device Area (1 mm²)	Custom laser cutting and dicing services.	We provide plates/wafers up to 125mm (PCD) and can precisely cut SCD devices to required dimensions (e.g., 1 mm²) with high yield.
Thin i-Layer (10 µm)	SCD epitaxial growth with thickness control (0.1 µm - 500 µm).	Precise control over the intrinsic layer thickness is critical for tuning the switching time and hold-off voltage (Eq. 2 & 3).
High-Quality Contacts (n⁺/p⁺)	Custom Boron Doping (BDD) and Metalization services.	We provide heavy BDD for p⁺ contacts. We also offer internal metalization (Au, Pt, Ti, W, Cu) to address the challenge of forming low-resistance n⁺ contacts (e.g., Ti/Pt/Au stacks).
Surface Finish	Polishing to Ra < 1nm (SCD).	Essential for high-quality homoepitaxy and minimizing surface defects that could prematurely trigger breakdown in high-field devices.
Substrate Thickness	Substrates up to 10mm thick.	Provides robust mechanical support for thin epitaxial layers in high-power device fabrication.

Engineering Support

The paper highlights the technological challenge of achieving efficient n-type doping in diamond (due to high activation energy), suggesting alternative methods like n-type surface doping or merged diodes (e.g., AlGaN/Diamond).

Doping Strategy Consultation: 6CCVD’s in-house PhD team possesses deep expertise in diamond material science and can assist researchers and engineers in selecting optimal doping strategies (including BDD concentration and alternative n-type approaches) for High-Power Avalanche Shaper projects.
Global Supply Chain: We offer global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond wafers to research facilities worldwide, accelerating the transition from simulation to physical device testing.

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

View Original Abstract

Diamond holds promise to reshape ultrafast and high-power electronics. One such solid-state device is the diode avalanche shaper (DAS), which functions as an ultrafast closing switch where closing is caused by the formation of the streamer traversing the diode much faster than 10 7 cm/s. One of the most prominent applications of DAS devices is in ultrawideband (UWB) radio/radar. Here, we simulate a diamond-based DAS and compare the results to a silicon-based DAS. All DASs were simulated in mixed mode as ideal devices using the drift-diffusion model. The simulations show that a diamond DAS promises to outperform an Si DAS when sharpening the kV nanosecond input pulse. The breakdown field and streamer velocity (∼10 times larger in diamond than Si) are likely to be the major reasons enabling kV sub-50 ps switching using a diamond DAS.

Tech Support

Original Source

DOI: https://doi.org/10.3389/frcrb.2023.1230873

References

2017 - A study of 4h-SiC diode avalanche shaper [Crossref]
1970 - Avalanche shock fronts in p-n junctions [Crossref]
2013 - Safety aspects of people exposed to ultra wideband radar fields [Crossref]
2011 - Note: picosecond impulse generator driven by cascaded step recovery diode pulse shaping circuit [Crossref]
1996 - New approaches for designing high voltage, high current silicon step recovery diodes for pulse sharpening applications [Crossref]
2006 - Ultrashort laser pulse phenomena
1997 - Powerful semiconductor 80 kv nanosecond pulser [Crossref]
2017 - Radar services in the 76-81 ghz band report and order - et docket no 15-26
1997 - Silicon diodes in avalanche pulse-sharpening applications [Crossref]
1996 - Simple techniques for the generation of high peak power pulses with nanosecond and subnanosecond rise times [Crossref]