Record performance in intrinsic, impurity-free lateral diamond photoconductive semiconductor switches

At a Glance

Metadata	Details
Publication Date	2025-04-01
Journal	Applied Physics Letters
Authors	Zhuoran Han, J. Lee, Anik Mazumder, Hubert N. Elly, Stephen Messing
Institutions	University of Illinois Urbana-Champaign
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Executive Summary

Demonstrates high-performance diamond photoconductive semiconductor switches (PCSS) using intrinsic, impurity-free type IIa diamond substrates.
Achieves a high normalized responsivity of 9.1x10^-8 A-cm/W-V and a peak photocurrent of 8.0 A.
Obtains a high on/off ratio of 2.3x10¹¹ at a DC bias of +1.2 kV.
Reports fast rise times (< 3 ns), limited by the laser’s rise time.
Shows that higher impurity levels reduce photocurrent and decrease the on/off ratio.
Highlights the advantages of using low background concentration type IIa diamond substrates for PCSS fabrication.
Presents a promising route toward advanced high-power, high-speed diamond-based switches.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Impurity Levels (B, N)	<10¹⁴ - 10¹⁶	cm^-3	Boron and Nitrogen impurity levels in type IIa diamond substrates
Laser Wavelength Range	212 - 240	nm	Incident laser wavelength range
Energy per Pulse	5 - 65	µJ	Incident laser pulse energy
DC Bias	-1.2 to +1.2	kV	Applied DC bias voltage
Normalized Responsivity	9.1x10^-8	A-cm/W-V	Highest achieved normalized responsivity
Peak Photocurrent	8.0	A	Peak photocurrent at +1.2 kV DC bias
On/Off Ratio	2.3x10¹¹	-	On/off ratio at +1.2 kV DC bias
Rise Time	< 3	ns	Rise time, limited by laser
Annealing Temperature	450	°C	Annealing temperature after metallization
Laser Pulse Width (FWHM)	4	ns	Full-width at half-maximum of the laser pulses
Spectral Bandwidth	0.1	nm	Spectral bandwidth of the laser
Beam Diameter	4	mm	Laser beam diameter incident on the PCSS surface
Load Resistance	47	Ω	Load resistor in the electrical test circuit
Capacitor Value	95	nF	Capacitor in the electrical test circuit
Minimum On-Resistance	115.07	Ω	Minimum PCSS on-resistance for PCSS A at 1.2kV
Fall Time (PCSS A at 1.2kV)	6.5	ns	Fall time (90%-10%) for PCSS A at 1.2kV

Key Methodologies

Substrate Preparation:
- Use type IIa diamond substrates (4.5 mm x 4.5 mm x 0.5 mm).
- Double-side polish the substrates.
- Characterize surface roughness using atomic force microscopy (AFM).
- Measure bulk boron and nitrogen concentrations using secondary ion mass spectrometry (SIMS).
Cleaning:
- RCA cleaning process to remove organic and metallic contaminants.
- Surface oxygen termination by treating in boiling H₂SO₄:HNO₃ mixture for 2 hours.
Metallization:
- Deposit Ti (30 nm) / Pt (30 nm) / Au (120 nm) layers via electron-beam evaporation.
- Electrode spacing: 2.1 mm.
- Electrode dimensions: 3.9 mm long and 0.9 mm wide.
Annealing:
- Anneal samples at 450 °C under Ar ambient for 1 hour.
Ozone Treatment:
- Treat devices with ozone at room temperature for 1 hour to stabilize oxygen-terminated surface.
Characterization:
- Use a tunable optical parametric oscillator (OPO) laser (212 nm to 240 nm, 4 ns pulse width, 10 Hz repetition rate).
- Control laser power using a half-wave plate and polarizing beam splitter.
- Apply DC bias (-1.2 kV to +1.2 kV).
- Measure photocurrent using a Tektronix CT6 current probe and a Tektronix DPO 7254C oscilloscope.

Commercial Applications

High Power RF
Pulsed Power Generation
Microwave Switching
High-Speed Switching Applications

View Original Abstract

Photoconductive semiconductor switches (PCSSs) are fabricated on type IIa diamond substrates with varying boron and nitrogen impurity levels (&lt;1014-1016 cm−3). The photoresponse of lateral PCSS is reported over the incident laser wavelength range (212-240 nm), energy per pulse (5-65 μJ), and DC bias (−1.2 to +1.2 kV). The PCSS device with the lowest boron and nitrogen impurity concentration achieves the highest normalized responsivity of 9.1 × 10−8 A-cm/W-V, peak photocurrent of 8.0 A, and on/off ratio of 2.3 × 1011 at a DC bias of +1.2 kV with the potential for even higher currents at increased DC bias. All PCSS display fast rise times (&lt;3 ns), limited by the laser’s rise time. However, photoresponse measurements reveal that higher impurity levels reduce the photocurrent and decrease the on/off ratio. These results highlight the performance advantages of using low background concentration type IIa diamond substrates for PCSS fabrication and present a promising route toward advanced high-power, high-speed diamond-based switches.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0266565

References

2010 - 1.55-μm GaNAsSb-based photoconductive switch for microwave switching [Crossref]
2012 - Performance and optimization of a 50 kV silicon carbide photoconductive semiconductor switch for pulsed power applications
2018 - Current state of photoconductive semiconductor switch engineering [Crossref]
2002 - Anisotropy in breakdown field of 4H-SiC [Crossref]
2021 - Impact ionization coefficients and critical electric field in GaN [Crossref]
2014 - High power operation of a nitrogen doped, vanadium compensated, 6H-SiC extrinsic photoconductive switch [Crossref]
2018 - High-gain persistent nonlinear conductivity in high-voltage gallium nitride photoconductive switches
2014 - Zr/oxidized diamond interface for high power Schottky diodes [Crossref]
2024 - High field transport in (ultra) wide bandgap semiconductors: Diamond versus cubic GaN [Crossref]
1992 - Unusually high thermal conductivity in diamond films [Crossref]