Quantum Dots Formed in Three-dimensional Dirac Semimetal Cd3As2 Nanowires
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-02-23 |
| Journal | Nano Letters |
| Authors | Minkyung Jung, Kenji Yoshida, Kidong Park, Xiao-Xiao Zhang, Can Yesilyurt |
| Institutions | National University of Singapore, Daegu Gyeongbuk Institute of Science and Technology |
| Citations | 20 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: Quantum Dot Confinement in Dirac Semimetals
Section titled â6CCVD Technical Documentation: Quantum Dot Confinement in Dirac SemimetalsâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a significant breakthrough in quantum device physics: the robust formation of a single quantum dot (QD) in a 3D Dirac semimetal ($\text{Cd}{3}\text{As}{2}$) nanowire. This work addresses the critical challenge of quantum confinement in gapless materials.
| Feature | Achievement | 6CCVD Relevance |
|---|---|---|
| QD Formation | Single p-type QD confirmed by clear Coulomb diamonds. | Requires ultra-stable, high-purity substrates for clean quantum transport. |
| Confinement Mechanism | Suppression of Klein tunneling via strong magnetic fields ($B \ge 8 \text{ T}$). | Experiments require robust, high-mobility platforms compatible with extreme cryogenic and magnetic environments. |
| Device Architecture | Electrostatically tuned $\text{n*}-\text{p}-\text{n*}$ junction using a global backgate and nanoscale $\text{Ti}/\text{Au}$ contacts. | 6CCVD specializes in custom metalized diamond substrates, ideal for integrating complex back-gating schemes and providing optimal thermal anchoring. |
| Operational Environment | Ultra-low temperature ($300 \text{ mK}$) and high field ($9 \text{ T}$) required for stable observation. | Diamondâs superior thermal properties are essential for managing heat dissipation and stabilizing QD states in cryogenic quantum systems. |
| Impact | Opens a new route for designing quantum devices (QDs, QPCs) based on Dirac/Weyl semimetals. | Drives demand for high-quality, customized diamond materials necessary for next-generation quantum engineering. |
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard parameters define the operational conditions and device characteristics required for observing stable quantum confinement in the $\text{Cd}{3}\text{As}{2}$ nanowires:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Measurement Temperature ($T$) | $\sim 300 \text{ mK}$ | K | Extremely low temperature required for resolving Coulomb blockade effects. |
| Critical Magnetic Field ($B$) | $8-9$ | T | Field strength required to suppress Klein tunneling and induce cyclotron motion. |
| Nanowire Diameter | $60-100$ | nm | Typical size range of the active $\text{Cd}{3}\text{As}{2}$ nanowire segment. |
| Channel Length | $\sim 250$ | nm | Separation distance between the source and drain metal contacts. |
| Electron Mobility ($\mu_{e}$) | $1300$ | $\text{cm}^{2}/\text{Vs}$ | Measured in the n-regime (significantly higher than hole mobility). |
| Hole Mobility ($\mu_{h}$) | $220$ | $\text{cm}^{2}/\text{Vs}$ | Measured in the p-regime. |
| Dirac Peak Gate Voltage ($\text{V}_{G}$) | $\sim -2.5$ | V | Location of the ambipolar transition point. |
| Metal Contact Stack | $\text{Ti}/\text{Au}$ ($5/100$) | nm | Thicknesses of Titanium and Gold used for ohmic source/drain contacts. |
| Addition Energy ($\text{E}_{\text{add}}$) | $2-4$ | meV | Energy required to add a single hole to the QD. |
| Zeeman Energy Shift ($\text{E}_{Z}$) | $\sim 8.35$ | meV | Calculated shift at $B=9 \text{ T}$ due to large g-factor in $\text{Cd}{3}\text{As}{2}$. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully combined specialized material growth with cryogenic high-field transport measurements and precision nanofabrication.
I. Nanowire Synthesis (Vapor Transport Method)
Section titled âI. Nanowire Synthesis (Vapor Transport Method)â- Source Material: $\text{Cd}{3}\text{As}{2}$ powder ($99%$, Alfa Aesar) placed in ceramic boats.
- Catalyst: Silicon substrate coated with $1 \text{ mM } \text{BiI}_{3}$ ($99.999%$) solution to form Bi catalytic nanoparticles.
- Growth Parameters:
- Powder source temperature: $450^\circ\text{C}$.
- Substrate temperature: $\sim 350^\circ\text{C}$.
- Atmosphere: Argon gas supplied at $200 \text{ sccm}$ under ambient pressure.
- Growth Orientation: Nanowires grew preferentially along the [112] direction.
II. Device Fabrication and Measurement Setup
Section titled âII. Device Fabrication and Measurement Setupâ- Substrate & Gate: Nanowires transferred onto a highly doped $\text{p}^{++}$ silicon substrate acting as a global backgate, insulated by $300 \text{ nm}$-thick $\text{SiO}_{2}$.
- Oxide Removal: An Ar plasma etch was used prior to contact deposition to remove the native oxide layer on the nanowire surface.
- Contact Metalization: $\text{Ti}/\text{Au}$ ($5 \text{ nm}/\text{100 nm}$) source and drain contacts fabricated, separated by $250 \text{ nm}$.
- Measurement Environment:
- Temperature: $T \sim 300 \text{ mK}$.
- Magnetic Field ($B$): Applied perpendicularly (up to $9 \text{ T}$) to the nanowire axis to induce cyclotron motion.
III. Confinement Mechanism
Section titled âIII. Confinement Mechanismâ- Electrostatic Junction: Applying $\text{V}_{G} < -2.5 \text{ V}$ forms an $\text{n*}-\text{p}-\text{n*}$ junction, creating a p-type Quantum Dot (QD) cavity between n-type leads.
- Klein Tunneling Suppression: At $B \ge 8 \text{ T}$, the transverse Lorentz force bends the Dirac fermion trajectories at the $\text{p-n}$ interfaces, dramatically reducing transmission probability (suppressing Klein tunneling) and forming resistive tunnel barriers.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research into Dirac semimetal quantum confinement, requiring extreme stability, precision metalization, and cryogenic compatibility, aligns perfectly with 6CCVDâs advanced MPCVD diamond product line.
Applicable Materials and Substrates
Section titled âApplicable Materials and SubstratesâTo replicate or extend this researchâespecially toward higher integration density or more stable thermal operationâ6CCVD recommends:
| 6CCVD Material | Application in Quantum Transport | Key Benefit |
|---|---|---|
| Optical Grade SCD | Substrates for heterostructures and nanowire growth/transfer. | Cryogenic Stability: Provides exceptional thermal conductivity (up to $2000 \text{ W}/\text{mK}$), crucial for thermal anchoring and stable QD measurements at $300 \text{ mK}$. |
| High Purity SCD | Platform for NV-center integration or low-noise measurements. | Surface Quality: Achievable polishing of $\text{Ra} < 1 \text{ nm}$ minimizes random potential fluctuations (UCFs) that contaminate sensitive transport data. |
| Boron-Doped Diamond (BDD) | Custom metallic gates, robust leads, or high-conductivity contact areas. | Conductivity Control: BDD offers tunable metallic properties, ideal for creating precise, low-resistance electrodes for probing semimetal devices. |
| PCD Wafers (Inch Size) | Large-scale integration of quantum point contact (QPC) arrays. | Scalability: Inch-size PCD wafers ($\text{up to } 125 \text{ mm}$) with $\text{Ra} < 5 \text{ nm}$ polishing support pilot-scale quantum device engineering. |
Customization Potential
Section titled âCustomization Potentialâ6CCVD provides the specialized engineering services required to accelerate Dirac semimetal and quantum device research:
- Precision Metalization Services: We offer in-house deposition of all materials used in standard quantum device fabrication, including the complex $\text{Ti}/\text{Au}$ (5 nm/100 nm) stacks required in this study, as well as $\text{Pt}$, $\text{Pd}$, $\text{W}$, and $\text{Cu}$. We ensure high adhesion and purity critical for cryogenic contacts.
- Custom Dimensions and Geometry: Unlike standard $\text{Si}/\text{SiO}_{2}$ wafers, 6CCVD provides custom dimensions and laser cutting services to shape diamond plates or substrates up to $10 \text{ mm}$ thick, facilitating seamless integration into high-field, ultra-low temperature cryostats.
- Dielectric Stacks: While this paper used $\text{SiO}{2}$, 6CCVD can integrate custom dielectric layers (e.g., $\text{Al}{2}\text{O}_{3}$) onto diamond substrates, offering higher capacitance and superior gate coupling for improved electrostatic control of $\text{p-n}$ junctions in $3\text{D}$ semimetals.
Engineering Support
Section titled âEngineering SupportâThe successful demonstration of magnetic confinement in a gapless material highlights complex material interaction challenges. 6CCVDâs in-house PhD team is available to assist researchers with:
- Material selection optimization for high-field quantum transport projects.
- Designing robust back-gate configurations utilizing BDD or low-strain SCD.
- Consultation on metal stack optimization for nanoscale contacts (channel length $\sim 250 \text{ nm}$) requiring high precision lithography.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd<sub>3</sub>As<sub>2</sub> nanowires using two electrostatically tuned p-n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the Cd<sub>3</sub>As<sub>2</sub> nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire. Our results show that a p-type QD can be formed between two n-type leads underneath metal contacts in the nanowire by applying gate voltages under strong magnetic fields. Analysis of the quantum confinement in the gapless band structure confirms that p-n junctions formed between the p-type QD and two neighboring n-type leads under high magnetic fields behave as resistive tunnel barriers due to cyclotron motion, resulting in the suppression of Klein tunneling. The p-type QD with magnetic field-induced confinement shows a single hole filling. Our results will open up a route to quantum devices such as QDs or quantum point contacts based on Dirac and Weyl semimetals.