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6CCVD Research

Observation of transferred-electron oscillations in diamond

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2019-11-04
JournalApplied Physics Letters
AuthorsN. Suntornwipat, S. Majdi, M. Gabrysch, Friel I, J. Isberg
InstitutionsElement Six (United Kingdom), Uppsala University
Citations2
AnalysisFull AI Review Included

Technical Analysis and Documentation for Diamond Transferred-Electron Devices (TEDs)

Section titled “Technical Analysis and Documentation for Diamond Transferred-Electron Devices (TEDs)”

Executive Summary

Section titled “Executive Summary”

This research demonstrates the first observation of Transferred-Electron Oscillations (TEO), also known as Gunn oscillations, in a bulk, intrinsic Single-Crystal Chemical Vapor Deposition (SC-CVD) diamond. This breakthrough confirms the viability of diamond for high-frequency microwave applications requiring Negative Differential Mobility (NDM).

  • Novelty: First successful demonstration of TEO in an elemental, indirect-bandgap semiconductor (diamond), utilizing intrinsic material properties for electron repopulation between conduction band valleys.
  • Operating Range: Continuous oscillations were observed across a wide thermal range (90 K to 300 K), demonstrating operation potential at or near room temperature.
  • Performance: Oscillations were observed in the 20 MHz to 50 MHz range, depending on the external LC resonant circuit configuration.
  • Material Requirement: Achieving the NDM effect mandates the use of ultra-high purity intrinsic SC-CVD diamond, specifically requiring impurity concentrations below 1014 cm-3.
  • Device Structure: The TEO devices were based on diamond wafers (307 ”m to 420 ”m thick) requiring custom-sputtered, semitransparent Ti/Al contact metalization on the (100) surface.
  • Core Value Proposition: This work establishes SC-CVD diamond as a foundational material for high-power, high-frequency oscillators and amplifiers, leveraging diamond’s superior thermal management and high carrier mobility.

Technical Specifications

Section titled “Technical Specifications”

The following hard data points were extracted detailing the material characteristics and observed device performance metrics.

ParameterValueUnitContext
Material Purity<1014cm-3Maximum impurity concentration (intrinsic SC-CVD)
Operating Temperature Range90 to 300KRange where transferred-electron oscillations were observed
Optimal Oscillation Temperature110 to 130KTemperature range showing maximum oscillator strength
Observed Frequency Range20 to 50MHzDepending on external LC circuit values
Maximum Applied Bias Voltage30VApplied across the diamond samples (~400 ”m thick)
Approximate Electric Field (NDM)300 to 600V/cmReported NDM range from referenced prior work [11]
Sample Thicknesses Tested307, 390, 420”mPrecision thickness required for device stability
Longitudinal Effective Mass (ml)1.56 m0N/AElectron effective mass in parallel valleys
Transverse Effective Mass (mt)0.28 m0N/AElectron effective mass in orthogonal valleys
Excitation Wavelength (HeAg Laser)224.3nmUsed to generate electron-hole pairs
UV Penetration Depth~200”mPenetration depth in intrinsic diamond
Metalization Stack20/300nmThicknesses of Sputtered Ti/Al layers

Key Methodologies

Section titled “Key Methodologies”

The experimental approach focused on precise material quality control and customized device integration into a resonant circuit under cryostat conditions.

  1. Material Selection: High-purity, intrinsic Single Crystal CVD (SC-CVD) diamond was utilized (Impurity Concentration <1014 cm-3). Samples were oriented on the (100) surface.
  2. Device Dimensioning: Three diamond plates were fabricated with controlled thicknesses ranging from 307 ”m to 420 ”m.
  3. Custom Contact Fabrication: Circular electrical contacts (3 mm diameter) were created using standard optical lithography techniques.
    • Contacts were deposited by sputtering Ti/Al (20 nm/300 nm) to form a semitransparent mesh, allowing UV photon access.
  4. Carrier Generation: A HeAg excimer laser (224.3 nm, 50 mW peak power, 100 ”s pulse length) was used to inject electron-hole pairs via UV illumination into the sample.
  5. Circuit Integration: The diamond sample was mounted on a gold-plated chip carrier and connected in series with an external LC resonance circuit (L: 1.8-10 ”H; C: 0-4.7 pF).
  6. Thermal Control: The setup was housed inside a vacuum cryostat and monitored (90 K to 300 K) using a GaAlAs diode sensor and liquid nitrogen cooling.
  7. Signal Acquisition: Current waveforms were amplified (Mini-Circuits ZFL1000LN+ or custom p-HEMT) and recorded using a high-speed digital oscilloscope (Tektronics TDS 684C, 5 GS/s) within a doubly shielded casing.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

This research highlights the critical reliance on ultra-high purity, custom-fabricated diamond substrates—an area where 6CCVD provides industry-leading solutions designed to accelerate similar research and commercialization efforts.

Research Requirement6CCVD Capability & SolutionValue Proposition
High Purity SC-CVD DiamondOptical Grade SCD with nitrogen concentration <1 ppb (Purity equivalent to or exceeding the material specified).Guarantees the necessary low impurity concentration (<1014 cm-3) essential for intervalley electron dynamics and NDM realization.
Precision Thickness ControlSCD fabrication capability from 0.1 ”m up to 500 ”m, and substrates up to 10 mm.We can precisely replicate the required 307 ”m, 390 ”m, and 420 ”m wafer thicknesses for TEO tuning, or provide thicker substrates for high-power devices.
Custom DimensionsPlates/wafers up to 125 mm (PCD) and custom laser cutting/dicing services.6CCVD can supply the required small-area chips (2.8 x 2.8 mm to 4.5 x 4.5 mm) quickly and with high dimensional accuracy for chip mounting.
Complex Metalization StacksInternal metalization services including Ti, Al, Pt, Au, Pd, W, and Cu deposition.We offer custom sputtering of Ti/Al (20/300 nm) stacks, crucial for forming the semitransparent Ohmic contacts needed for this UV-driven TEO mechanism.
Surface Quality (Lithography)Advanced mechanical and chemical polishing services. SCD surfaces polished to Ra < 1 nm.Ensures atomic-level flatness required for precise optical lithography used in defining 3 mm diameter contacts and optimizing charge transport properties.
International LogisticsGlobal shipping (DDU default, DDP available).Ensures rapid, secure, and fully compliant delivery of sensitive, high-value diamond materials worldwide.

Engineering Support

Section titled “Engineering Support”

6CCVD’s in-house PhD material science and engineering team is prepared to assist clients replicating or extending this research into next-generation microwave and high-frequency oscillator projects. We provide tailored consultation on:

  • Selecting optimal SCD or BDD materials to achieve specific carrier concentrations and mobility requirements.
  • Designing and fabricating customized metalization schemes (e.g., Ohmic or Schottky contacts) for high-temperature/high-power microwave circuits.
  • Material orientation (e.g., (100) vs (111)) optimization based on specific transport physics requirements.

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

View Original Abstract

The transferred-electron oscillator (TEO), or Gunn oscillator, is a device used in microwave applications, which utilizes the negative differential mobility (NDM) effect to generate continuous oscillations. Recently, NDM was observed in intrinsic single-crystalline chemical vapor deposition (SC-CVD) diamond. The occurrence was explained by the electron repopulation between its different conduction band valleys. This paper presents the results of constructing a diamond TEO based on the NDM effect. A series of experiments have been performed for varying voltages, temperatures, and resonator parameters on three SC-CVD diamond samples of different thicknesses. For the temperature range of 90-300 K, we observe transferred-electron oscillations in diamond.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - Semiconductor Devices: Physics and Technology

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