NV Center Charge State Controlled Graphene-on-Diamond Field Effect Transistor Actions With Multi-Wavelength Optical Inputs
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | IEEE Open Journal of Nanotechnology |
| Authors | Yonhua Tzeng, Ying-Ren Chen, Pinyi Li, Chun-Cheng Chang, YuehâChieh Chu |
| Institutions | National Cheng Kung University |
| Citations | 5 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel Graphene-on-Diamond Field Effect Transistor (GFET) whose electrical conductivity is controlled by the optically excited charge state of Nitrogen-Vacancy (NV) centers within the diamond substrate.
- Core Mechanism: The negative charge state (NV-) in the diamond acts as a gate bias, enhancing hole concentration in the p-type graphene channel. Optical illumination converts NV- to neutral NV° (or vice versa), modulating the channel conductivity via field effects.
- Wavelength-Dependent Polarity: The device exhibits wavelength-dependent differential conductance polarity, a key achievement not previously reported for GFETs with multiple optical inputs.
- Blue Laser Input (405 nm): Induces positive differential conductance (current increases), primarily converting NV° back to NV-.
- Red Laser Input (633 nm): Induces negative differential conductance (current decreases), primarily converting NV- to NV°.
- Multi-Input Control: By simultaneously illuminating the device with both red and blue lasers, the net differential conductance can be precisely controlled or even canceled, demonstrating a multi-input optical logic function.
- Material Quality: Monolayer graphene synthesized via low-pressure thermal CVD exhibited high quality, confirmed by a Raman 2D/G ratio of ~2.5 and a calculated field-effect mobility of 400 cm2/Vs.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Graphene Type | Monolayer | N/A | Synthesized via Low-pressure thermal CVD |
| Graphene Mobility (”) | 400 | cm2/Vs | Measured on SiO2/Si back-gate FET |
| Graphene Domain Size | ~400 | ”m | Before merging into continuous film |
| CVD Reaction Temperature | 1040 | °C | Graphene synthesis on copper foil |
| Vacuum Pressure (Testing) | 4 x 10-5 | Torr | Operating environment for optical tests |
| Applied Voltage (VDS) | 1 or 20 | V | Source-Drain voltage during conductance measurement |
| Blue Laser Wavelength | 405 | nm | 3.06 eV photon energy |
| Green Laser Wavelength | 532 | nm | 2.33 eV photon energy |
| Red Laser Wavelength | 633 | nm | 1.96 eV photon energy |
| NV- to NV° Conversion | 2 Red or 1 Blue | Photons | Excitation of electron to conduction band (CB) |
| NV° to NV- Conversion | 1 Blue | Photon | Excitation of electron from valence band (VB) |
| Graphene Optical Absorption | ~2.3 | % | Absorption of incident light by monolayer |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure involved high-quality graphene synthesis, transfer, device fabrication, and specialized optical testing in a controlled environment.
- Graphene Synthesis: Monolayer graphene was grown on copper foils using low-pressure thermal Chemical Vapor Deposition (CVD) at a reaction temperature of 1040 °C, utilizing gas mixtures of methane (CH4), hydrogen (H2), and argon (Ar).
- Material Characterization: Graphene quality was verified using Raman spectroscopy (2D/G ratio ~2.5) and electrical measurements, yielding a field-effect mobility of 400 cm2/Vs.
- Device Fabrication (GFET): Monolayer graphene was transferred onto single-crystalline High-Pressure High-Temperature (HPHT) diamond substrates (Type Ib, containing abundant NV centers). Palladium (Pd) metal contacts were deposited via RF magnetron sputtering and lift-off to form the Source and Drain electrodes.
- Optical Setup: The test device was placed inside a vacuum chamber evacuated to 4 x 10-5 Torr. Three solid-state lasers (405 nm, 532 nm, 633 nm) were aligned to illuminate the 10 ”m or 400 ”m graphene channel gap, individually or simultaneously.
- Differential Conductance Measurement: A fixed voltage (1 V or 20 V) was applied across the Pd contacts. The change in current (differential conductance) was measured as the laser beams were cyclically turned on (1 minute) and off (1 minute).
- Multi-Wavelength Control: Experiments were conducted to demonstrate cancellation effects by balancing the power of the red (negative conductance) and blue (positive conductance) lasers, showing that the net current flow could be maintained nearly constant regardless of illumination state.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology, leveraging the stable quantum properties of NV centers in diamond and the high sensitivity of graphene FETs, is relevant to several advanced engineering fields:
- Quantum Sensing and Metrology: NV centers are primary candidates for nanoscale sensing (magnetometry, thermometry). Integrating the NV centers directly into the FET gate structure allows for electrical readout of quantum state changes, potentially leading to highly localized, electrically addressable quantum sensors.
- Optically Controlled Logic and Memory: The ability to switch the channel conductivity polarity based on input wavelength (Blue/Red) enables novel optical logic gates or optically addressable memory elements where the NV charge state stores the bit.
- Wide-Spectral Photodetectors: While graphene alone has low absorption, the NV-diamond substrate enhances photoresponse. The wavelength-dependent polarity allows the device to function as a multi-color photodetector capable of distinguishing input wavelengths based on the sign of the electrical output.
- Harsh Environment Electronics: Diamondâs exceptional thermal, chemical, and mechanical stability makes this platform ideal for electronics operating in extreme conditions (high temperature, radiation).
- Integrated Photonics: The device structure provides a pathway for integrating optical inputs (lasers) with electrical outputs (FETs) on a robust diamond platform, suitable for future optoelectronic integrated circuits.
View Original Abstract
We demonstrate graphene-on-diamond field effect transistor (FET) actions modulated by optically excited charge state of nitrogen-vacancy (NV) centers in diamond. Palladium (Pd) metal contacts on graphene serve as the source and the drain. Negative charge state NV<sup>-</sup> center in diamond serves as the gate with diamond being the gate dielectric and produces an electric field to enhance the hole concentration in the graphene channel. The conductivity of graphene varies with negative charge state NV<sup>-</sup> center, resulting in differential conductance. The negative gate bias is removed when a NV<sup>-</sup> center is converted to an NV<sup>o</sup> center. P-type graphene channel exhibits positive differential conductance under illumination by a blue (405 nm) laser beam while on the contrary negative differential conductance by a red (633 nm) laser beam. Furthermore, by simultaneous illumination of both blue and red laser beams, effects on differential conductance decrease according to the relative intensity of the two laser beams. Graphene FETs with wavelength dependent multiple optical inputs and one electrical output in response to the charge state of NV centers in diamond has been reported.