A Valleytronic Diamond Transistor - Electrostatic Control of Valley Currents and Charge-State Manipulation of NV Centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-18 |
| Journal | Nano Letters |
| Authors | Nattakarn Suntornwipat, Saman Majdi, Markus Gabrysch, Kiran Kumar Kovi, Viktor Djurberg |
| Institutions | Uppsala University, Element Six (United Kingdom) |
| Citations | 18 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the realization of a valleytronic diamond field-effect transistor (FET) capable of all-electric control over electron valley pseudospin states.
- Core Innovation: Successful demonstration of electrostatic control over valley-polarized electron currents in a dual-gate diamond FET, eliminating the need for strong external magnetic fields.
- Material Platform: Utilizes ultra-pure single-crystalline diamond, leveraging its extreme lattice rigidity to achieve highly stable valley states (intervalley scattering rate < 104 s-1 below 80 K).
- Dual Control Mechanism: The double-gate configuration allows for separate, independent control of the total charge current and the valley-current polarization arriving at the drain electrodes.
- High Fidelity Modulation: Simulations show the contribution of specific valleys (e.g., (001) valleys) to the total collected charge can be modulated with high fidelity, ranging from 10% to 90%.
- Application Demonstrated: Valley-currents were used to achieve local, electrical charge-state manipulation (modulation) of nitrogen-vacancy (NV) centers in the diamond layer, monitored via electroluminescence (EL).
- Validation: Experimental time-resolved current measurements show excellent agreement with theoretical models based on drift-diffusion equations coupled with microscopic Monte Carlo simulations.
- Significance: Provides a rapid, scalable solid-state platform for valleytronic information processing and electrical pumping of diamond color centers for quantum applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Purity (N) | < 0.05 | ppb | Nitrogen impurity concentration in CVD diamond plates. |
| Ionized Impurity Conc. | < 1010 | cm-3 | Concentration used in Monte Carlo simulations. |
| Gate Dielectric Thickness | 30 | nm | Al2O3 layer deposited via ALD. |
| Operating Temperature | 78 | K | Experimental temperature for time-resolved current measurements. |
| Valley Stability (Low T) | < 104 | s-1 | Intervalley scattering rate below ~80 K. |
| Effective Mass Ratio | â 5.5 | Unitless | Ratio of transversal (mT) to longitudinal (m||) effective mass (mT / m||). |
| Excitation Wavelength | 213 | nm | Passively Q-switched laser used for electron-hole pair generation. |
| Pulse Width (FWHM) | 800 | ps | Duration of the UV laser pulse. |
| Peak Carrier Conc. | < 1010 | cm-3 | Concentration limit used to minimize electron-electron scattering. |
| Bandgap Energy (Egap) | 5.47 | eV | Diamond bandgap energy. |
| Photon Energy (hv) | 5.82 | eV | Energy of the 213 nm excitation photons. |
| NV Layer Thickness | 120 | nm | Thin layer containing NV centers below top electrodes. |
| NV Implantation Dose | ~1013 | cm-2 | Total dose range for 14N implantation (across three energy levels). |
| (001) Valley Modulation | 10% to 90% | % of total charge | Simulated fidelity of valley pseudospin control at drain D2. |
| Acoustic Def. Potential (DL) | 12.0 | eV2 | Parameter used in Monte Carlo simulations (Supporting Information). |
| f/g-Scattering Potential (Df, Dg) | 4 x 108 | eV/cm | Parameter used in Monte Carlo simulations (Supporting Information). |
| Drain Current Measurement | 3 | GHz | Bandwidth of low-noise amplifiers used for current detection. |
Key Methodologies
Section titled âKey MethodologiesâThe devices were fabricated on ultra-pure, freestanding single-crystalline CVD (001) diamond plates from Element Six Ltd.
- Material Preparation: Diamond plates (4.5 x 4.5 mm, 390 to 510 ”m thick) with nitrogen impurity concentration below 1013 cm-3 were used to minimize ionized impurity scattering.
- NV Center Creation:
- The top (001) surface was ion-implanted with 14N at room temperature using three energy levels (30 keV, 60 keV, 90 keV) to create a thin NV layer.
- The sample was subsequently annealed at 800 °C for 2 hours.
- Dielectric Deposition: A 30 nm Al2O3 oxide layer was deposited on the oxygen-terminated surface using Atomic Layer Deposition (ALD) at 300 °C, utilizing trimethylaluminum and ozone precursors.
- Contact Metallization:
- Openings in the oxide were created via lithography and hydrofluoric (HF) etching.
- Source, gate, and drain contacts were formed by evaporating Ti/Al (20 nm/300 nm).
- The back (001) surface was metallized with 10 nm Au to provide a semitransparent ground contact.
- Charge Transport Measurement:
- Samples were mounted in a vacuum cryostat (78 K) with UV optical access.
- Electrons were generated using short (800 ps) 213 nm UV pulses.
- Time-resolved induced currents at the drains were measured using broadband low-noise amplifiers (50 Ω input) and a digital sampling oscilloscope (3 GHz, 10 GS/s).
- Modeling and Simulation:
- Charge transport was modeled using coupled drift-diffusion and Poisson equations, incorporating three effective electron concentrations corresponding to the three principal valley axes.
- Electric field dependence of intervalley relaxation time (Î) and carrier temperature (Te) was determined using microscopic Monte Carlo simulations.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated technology provides fundamental capabilities crucial for emerging fields in solid-state physics and quantum technology.
| Application Area | Specific Use Case / Product Relevance |
|---|---|
| Quantum Information Processing (QIP) | Provides a scalable, all-electric method for manipulating electron pseudospin, a potential resource for quantum bits (qubits) or quantum interconnects. |
| Single Photon Sources | Enables electrical pumping of diamond color centers (NV centers) by delivering highly valley-polarized electrons, potentially leading to ultrabright, electrically driven single-photon sources at room temperature. |
| Quantum Sensing / Magnetometry | The ability to locally manipulate the charge state of NV centers (NV0/NV-) via gate bias is critical for optimizing the spin state readout and performance of NV-based magnetometers. |
| Valleytronics Devices | Forms the basis for novel valleytronic components, such as all-electric controlled valley filters, valves, and universal reversible logic gates, leveraging the anisotropic transport properties of diamond. |
| High-Speed Electronics | Diamondâs high electron mobility and stable material properties, combined with the demonstrated FET structure, are relevant for high-power and high-frequency electronic devices, though the valley control is the primary focus here. |
View Original Abstract
The valley degree of freedom in many-valley semiconductors provides a new paradigm for storing and processing information in valleytronic and quantum-computing applications. Achieving practical devices requires all-electric control of long-lived valley-polarized states, without the use of strong external magnetic fields. Because of the extreme strength of the carbon-carbon bond, diamond possesses exceptionally stable valley states that provide a useful platform for valleytronic devices. Using ultrapure single-crystalline diamond, we demonstrate electrostatic control of valley currents in a dual-gate field-effect transistor, where the electrons are generated with a short ultraviolet pulse. The charge current and the valley current measured at the receiving electrodes are controlled separately by varying the gate voltages. We propose a model to interpret experimental data, based on drift-diffusion equations coupled through rate terms, with the rates computed by microscopic Monte Carlo simulations. As an application, we demonstrate valley-current charge-state modulation of nitrogen-vacancy centers.