Comparative analysis of the millimeter wave performance of diamond based IMPATT diode with that of SiC (4H) IMPATT diode

At a Glance

Metadata	Details
Publication Date	2015-06-22
Journal	Indian Journal of Pure & Applied Physics
Authors	Dipankar Ghosh, Chakrabarti Bibek, Monojit Mitra
Citations	1
Analysis	Full AI Review Included

6CCVD Technical Analysis & Market Opportunity: Diamond IMPATT Diodes

Source Paper: Comparative analysis of the millimeter wave performance of diamond based IMPATT diode with that of SiC (4H) IMPATT diode (Chakrabarti et al., 2014)

Executive Summary

This analysis confirms the superior thermal and electrical performance of diamond DDR (Double Drift Region) IMPATT diodes compared to 4H-SiC devices, specifically for high-power, millimeter-wave (W-band, 75-110 GHz) applications.

Peak Efficiency Advantage: Optimized Diamond IMPATT devices achieved a simulated efficiency of 18.45%, significantly outperforming the 4H-SiC counterpart (11.97%).
High RF Power Generation: Diamond exhibited a peak negative conductance (-G_p) approximately 30 times higher than 4H-SiC, indicating superior potential for RF power output.
Unmatched Thermal Management: Diamond’s thermal conductivity (24 W/cm-K) drastically simplifies heat sink requirements, allowing the use of smaller, cost-effective copper heat sinks (280 µm diameter) for safe operation (514 K junction temperature).
Reduced Heat Sink Cost: In contrast, 4H-SiC devices require large, high-cost diamond heat sinks (900 µm diameter) just to maintain thermal stability.
Structure and Growth Complexity: Replicating the optimized DDR structure requires precise control over µm-scale active layer thickness and high-density doping profiles (10²³ m^-3 scale), directly aligning with 6CCVD’s advanced MPCVD capabilities.
Photosensitivity Implications: While both materials degrade under optical illumination due to increased photo-generated carriers, the overall small signal performance degradation is more intense in diamond due to its very high reported carrier ionization rates.

Technical Specifications

Material Properties Comparison (Diamond vs. Traditional WBG Semiconductors)

Parameter	Si	GaAs	4H-SiC	GaN (Wz)	Diamond	Unit	Context
Bandgap (E_g)	1.1	1.4	3.2	3.4	5.5	eV	Highest of all compared materials.
Breakdown Field (E_c)	0.3	0.4	3	5	20	MV/cm	Highest field strength achieved.
Electron Mobility (µ_n)	1450	8500	900	2000	4500	cm²/V-s	Crucial for fast response devices.
Hole Mobility (µ_p)	480	400	120	200	3800	cm²/V-s
Thermal Conductivity (k)	1.5	0.55	3.7	1.3	24	W/cm-K	Highest of all materials.
Saturation Velocity (v_ns)	1	1	2	2.2	1.2	x10⁷ cm/sec

Diamond IMPATT Diode Performance Data (W-Band)

Parameter	Value (Diamond)	Value (4H-SiC)	Unit	Context
Efficiency (η)	18.45	11.97	%	Optimized, unilluminated state.
Breakdown Voltage (V_B)	92.6	919	V	Significantly lower V_B required for Diamond IMPATT.
Peak Electric Field (E_m)	0.936 x10⁸	2.31 x10⁸	V/m	Field at the metallurgical junction.
Peak Frequency (f_p)	104	93	GHz	W-band operation.
Peak Negative Conductance (-G_p)	-8.39	-0.264	10⁸ Sm^-2	30x higher for Diamond.
Total Negative Resistance (-Z_R)	-4.43	-0.279	10^-8 Ωm²	Indicator of RF power potential.
Quality Factor (Q)	1.2	36.7	None	Lower Q indicates better performance for IMPATT.

Optimized Heat Sink Requirements

Diode Type	Heat Sink Material	Diameter (D)	Thickness (L)	Thermal Resistance (R_th)	Junction Temperature
Diamond DDR	Copper	280 µm	700 µm	29.47 °C/watt	514 K
4H-SiC DDR	Diamond	900 µm	700 µm	2.76 °C/watt	515 K
Observation: Diamond devices allow a 3.2x smaller diameter heat sink using lower-cost Copper while maintaining the required thermal stability (500 K safe operating temperature).

Key Methodologies

The study utilized a comprehensive simulation scheme comparing optimized DDR (n⁺⁺, n, p, p⁺⁺) structures for both diamond and 4H-SiC.

Structural Definition: A flat-profile Double Drift Region (DDR) structure was modeled, consisting of highly doped substrates and cap layers (n⁺⁺/p⁺⁺) and the active epilayer (n/p regions).
DC Analysis: Poisson and carrier current continuity equations were solved iteratively across the depletion layer to obtain DC electric field profiles and breakdown voltage (V_B).
Simulation Parameters:
- Monte Carlo simulated values were used for diamond drift velocity and mobility.
- Theoretical predicted values were used for diamond ionization coefficients due to lack of experimental data.
Small Signal Analysis: The Gummel-Blue method was employed to compute the diode impedance (Z), admittance (Y), negative conductance (-G), and susceptance (B) across the W-band frequency range.
Optimized Diode Design Parameters (Table 2):

Diode Type	Width of n region (W_n) (µm)	Width of p region (W_p) (µm)	Doping Conc. n region (10²³ m^-3)	Doping Conc. p region (10²³ m^-3)	Current Density (10⁸ Am^-2)
SiC-4H	2.4	2.4	0.18	0.2	1
Diamond	0.930	0.812	0.31	0.33	1

Thermal Analysis: Thermal resistance (R_th) was calculated for a cylindrical block heat sink structure (R_th = L / (A * k)), considering the thermal properties of the material, radius (r), and length (L) necessary to keep the junction temperature around 500 K.

6CCVD Solutions & Capabilities

This research validates diamond as the superior material for high-power, high-frequency solid-state sources, primarily due to its combination of high carrier mobility and world-leading thermal conductivity. 6CCVD is uniquely positioned to supply the materials required to replicate, optimize, and advance this technology.

Applicable Materials

The complex DDR structure requires ultra-high quality, precisely doped MPCVD material layers.

Diode Requirement	6CCVD Material Solution	Customization/Benefit
Active Drift Layers (n/p)	Single Crystal Diamond (SCD) Epilayers	SCD provides the purity and structural integrity necessary for high carrier mobility and controlled µm-scale thickness (down to 0.1 µm).
Highly Doped Substrates (n⁺⁺/p⁺⁺)	Boron-Doped Diamond (BDD)	BDD substrates or heavily doped SCD layers are essential for achieving the high doping concentrations (10²³ m^-3) and low resistivity required for contacts.
Heat Sink Material	Polycrystalline Diamond (PCD) Wafers	For applications requiring extreme thermal management (like the SiC case, or optimizing high-power diamond devices further), 6CCVD offers large format PCD (up to 125mm) with outstanding thermal performance.

Customization Potential

The optimized diamond DDR structure (W_n=0.930 µm, W_p=0.812 µm) demands sub-micron control over layer thickness and precise doping profiles, which are core 6CCVD competencies.

Precision Thickness Control: 6CCVD guarantees layer thickness control for both SCD and PCD from 0.1 µm up to 500 µm, allowing precise realization of the required drift regions (n and p).
Custom Doping: We specialize in controlled n-type (e.g., nitrogen/phosphorus incorporation) and p-type (Boron) doping profiles to meet the specific 10²³ m^-3 concentration needs of the DDR structure.
Metalization Services: The MESA structure (Fig. 1) requires high-quality ohmic contacts (Au, Pt, Cu). 6CCVD provides internal metalization services, including Ti, Pt, Au, W, or Cu layers, ensuring minimized contact resistance (R_{contact_down}) critical for thermal dissipation and efficient device performance.
Polishing Quality: Achieving an optimal interface between the active layers and contacts is vital. 6CCVD offers ultra-smooth polishing (Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD).

Engineering Support

The successful fabrication of diamond IMPATT devices hinges on mitigating issues like precise doping compensation, controlling ionization rates, and ensuring optimal thermal contact design.

6CCVD’s in-house PhD engineering team offers consultative support for customers engaged in similar high-frequency/high-power projects. We assist in:

Selecting the appropriate SCD/PCD grade and thickness for specific frequency bands (e.g., W-band, Terahertz).
Designing complex doping profiles necessary for DDR and SDR structures.
Optimizing metalization stack chemistry and thickness for minimizing thermal resistance and maximizing RF performance.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally, providing DDU default and DDP options for simplified worldwide procurement.

View Original Abstract

A detailed comparative analysis of the diamond semiconductor based DDR IMPATT devices in W-band has been carried out (normal and photo illuminated) through a simulation scheme. The simulation results reveal that an optimized unilluminated diamond IMPATT diode of efficiency 18.45% can be realized, whereas 4H-SiC IMPATT can have efficiency of 11.97%. Under optical illumination, the admittance and negative resistance values of the IMPATT diode degrade due to additional photo generated carriers. The negative conductance (-G) and total negative resistance (-Z R ) of the diamond based DDR IMPATT diode decrease by 7.03% and 8.5%, respectively when the diode is exposed to photo illumination whereas, for SiC based diode the decrements are 6.06% and 6.09%, respectively. Moreover under optical illumination, the quality factor ( Q p ) of diamond IMPATT increases by 22.5% and it is only 6.5% for SiC based devices. Therefore, from the simulation work it is well established that, though the photosensitivity of 4H-SiC based IMPATT is better than its diamond counterpart the overall small signal performance of the illuminated diamond IMPATT degrades far more than SiC based devices due to very high reported carrier ionization rates in diamond. The simulation results also reveal the superiority of diamond based IMPATT device in terms of heat sink design in comparison to 4H-SiC based devices.

Tech Support

Original Source

DOI: None