High Current Density Diamond Photoconductive Semiconductor Switches With a Buried, Metallic Conductive Channel

At a Glance

Metadata	Details
Publication Date	2024-04-10
Journal	IEEE Electron Device Letters
Authors	Zhuoran Han, J. Lee, Stephen Messing, Thomas Reboli, Andrey E. Mironov
Institutions	University of Illinois Urbana-Champaign
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: High Current Density Diamond PCSS

Executive Summary

This research demonstrates a significant advancement in high-power switching technology by introducing a laterally configured diamond Photoconductive Semiconductor Switch (PCSS) featuring a buried, metallic p+ conductive channel.

High Current Density: Achieved a peak current density of 43.5 A/cm under 60 V DC bias, significantly higher than previous linear-mode diamond PCSS devices.
Enhanced Reliability: The buried channel design enables linear-mode operation, concentrating current flow and eliminating the need for carrier multiplication and damaging filamentation common in high-gain switches.
Ultra-Fast Switching: The use of low-impurity, semi-insulating diamond as the active absorption layer resulted in fast rise and fall times of approximately 2 ns.
Exceptional Performance Metrics: The devices exhibited large ON/OFF ratios exceeding 10¹¹ and a high responsivity of 130.3 mA/W using above-bandgap optical triggering (λ < 226 nm).
Material Structure: The device relies on precise MPCVD growth of a heavily Boron-Doped (p+) diamond channel (500 nm, 5 x 10²⁰ cm^-3) beneath a 1.5 µm unintentionally doped (UID) active layer.
Core Value Proposition: Diamond’s superior properties (high critical E-field, high thermal conductivity) combined with the buried channel architecture promise highly reliable, high-power switching solutions for pulsed power applications.

Technical Specifications

The following table summarizes the critical material and performance parameters extracted from the research paper.

Parameter	Value	Unit	Context
Substrate Material	Type IIa HPHT Diamond	500 µm	4 x 4 mm² size
Buried Channel Material	Heavily Boron-Doped (p+) Diamond	500 nm	MPCVD grown
Buried Channel Doping (B)	5 x 10²⁰	cm^-3	Required for metallic conductivity
Active Layer Material	Unintentionally Doped (UID) Diamond	1.5 µm	Semi-insinsulating, MPCVD grown
Active Layer Doping (B)	5 x 10¹⁵	cm^-3	Low impurity concentration
Maximum Current Density (J)	43.5	A/cm	PCSS A, 60 V DC bias
Peak Responsivity	130.3	mA/W	PCSS A, 212 nm excitation
ON/OFF Ratio	> 10¹¹	Dimensionless	Achieved via semi-insulating layer
Switching Speed (Rise/Fall Time)	~2	ns	10-90% time, limited by laser pulse
Optical Trigger Wavelength	212	nm	Above-bandgap excitation
DC Bias Voltage Tested	± 60	V	Linear current-voltage characteristics observed
Metal Contact Stack	Ti/Pt/Au	30/30/100 nm	E-beam evaporated
Annealing Temperature	450	°C	Annealed in Ar atmosphere

Key Methodologies

The fabrication and testing of the diamond PCSS relied on precise MPCVD growth and controlled metalization processes.

Substrate Selection: High-pressure, high-temperature (HPHT) Type IIa diamond substrates (500 µm thick) were used as the base material.
MPCVD Epitaxial Growth: Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) was used to grow the functional layers.
Buried Channel Deposition: A 500 nm layer of heavily Boron-Doped (p+) diamond was grown first, serving as the low-resistance conductive channel.
Active Layer Deposition: A 1.5 µm layer of unintentionally doped (UID) diamond was grown on top, acting as the semi-insulating active absorption layer.
Metalization: Rectangular metal contacts composed of Ti/Pt/Au (30/30/100 nm) were deposited via e-beam evaporation.
Contact Annealing: The contacts were thermally annealed at 450 °C for 1 hour under an Argon (Ar) atmosphere to optimize contact resistance under illumination.
Optical Triggering Setup: A tunable Optical Parametric Oscillator (OPO) laser (4 ns FWHM pulse, 10 Hz repetition rate) was used for above-bandgap excitation (210 nm to 230 nm range).
Electrical Testing: Lateral PCSS structures (electrode spacings of 8 µm, 50 µm, and 100 µm) were characterized using a DC power supply and a high-speed oscilloscope (Tektronix DPO 7254C) with 50 Ω input impedance.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate, scale, and extend the performance demonstrated in this high-current PCSS research. Our capabilities directly address the need for precise doping, controlled thickness, and custom metalization essential for the buried channel architecture.

Applicable Materials & Requirements	6CCVD Solution & Capability	Technical Advantage for Customer
High-Purity Active Layer (1.5 µm UID, low B concentration)	Optical Grade Single Crystal Diamond (SCD)	We provide high-quality SCD films (0.1 µm to 500 µm thickness) with extremely low impurity levels, ensuring the high OFF-state resistance (> 10¹¹) and fast carrier lifetime (~2 ns) necessary for high-efficiency switching.
Buried Conductive Channel (500 nm, 5 x 10²⁰ cm^-3 p+)	Heavy Boron-Doped Diamond (BDD)	6CCVD specializes in custom BDD growth. We can precisely control the heavy p+ doping concentration and layer thickness (down to 0.1 µm) required to achieve the low-resistance “metallic” channel for high current handling (44 A/cm).
Custom Dimensions & Substrates (4 x 4 mm² device size)	Custom Plates and Substrates	We supply SCD and PCD plates up to 125 mm in diameter and substrates up to 10 mm thick, easily accommodating the required 4 x 4 mm² dimensions and providing capacity for large-scale device fabrication.
Metal Contact Stack (Ti/Pt/Au 30/30/100 nm)	In-House Custom Metalization Services	6CCVD offers internal metalization capabilities, including deposition of Ti, Pt, and Au stacks via e-beam evaporation, matching the exact requirements for the Schottky/Ohmic contacts used in this PCSS design. We also offer Pd, W, and Cu.
Surface Quality (Required for lithography)	Ultra-Low Roughness Polishing	Our SCD material is polished to an industry-leading surface roughness of Ra < 1 nm, ensuring optimal conditions for subsequent cleanroom processing and high-resolution lithography.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers can assist researchers and manufacturers in optimizing diamond material selection for high-power Photoconductive Semiconductor Switch (PCSS) projects. We offer consultation on epitaxial layer design, doping profiles, and metalization schemes to maximize current density and switching speed.

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

View Original Abstract

Laterally configured diamond photoconductive semiconductor switches (PCSS) with a buried, metallic p+ current channel are reported. Above bandgap ( λ ≤ 226 nm) optical triggering enables responsivity of over 130 mA/W. The use of low-impurity semi-insulating diamond as an active absorption layer enables fast rise and fall times (~2 ns) and on/off ratios greater than 10<sup>11</sup>. The PCSS excited with a laser energy of 20 nJ per pulse passes a high current density (44 A/cm) under a DC bias of 60 V, thanks to the buried metallic p+ current channel. The reported devices promise high current carrying capacity without the need for filamenting while leveraging the excellent optical, electronic, and thermal properties of diamond.

Tech Support

Original Source

DOI: https://doi.org/10.1109/led.2024.3387325