| Metadata | Details |
|---|
| Publication Date | 2023-05-04 |
| Journal | Nano Letters |
| Authors | Artur Lozovoi, YunHeng Chen, György Vizkelethy, Edward S. Bielejec, Johannes Flick |
| Institutions | City College of New York, Australian National University |
| Citations | 11 |
| Analysis | Full AI Review Included |
This research investigates the fundamental physics of carrier capture by individual point defects, overcoming limitations inherent in traditional ensemble measurements (like carrier screening and defect proximity).
- Core Achievement: First measurement of photo-generated hole capture probability by an individual negatively-charged Nitrogen-Vacancy (NV-) center in diamond under variable external electric fields at room temperature.
- Key Finding (Capture Dynamics): The hole capture probability exhibits an asymmetric bell-shaped dependence on the electric field, peaking sharply at zero voltage.
- Methodological Advance: An alternating current (AC) gating protocol (switching frequency >10 kHz) was successfully implemented to suppress metastable space-charge potentials, yielding the true space-charge-compensated capture rate.
- Quantified Cross Section: The measured hole capture cross section (Ïh(Exp)) is exceptionally large, approximately 3 x 10-11 cm2, which is 2 to 4 orders of magnitude greater than previously reported values for Coulombic attractive traps in ensemble studies.
- Theoretical Validation: Observations were accurately reproduced using semi-classical Monte Carlo simulations that model carrier trapping as a cascade process involving inelastic phonon emission.
- Implication: The large cross sections observed are anticipated to be present in other wide bandgap materials platforms due to the insensitivity of the cascade mechanism to specific trap characteristics.
| Parameter | Value | Unit | Context |
|---|
| Defect Studied | Nitrogen-Vacancy (NV-) center | N/A | Individual point defect in diamond. |
| Host Material | Electronic Grade Diamond | N/A | High purity, low screening effects. |
| Operating Temperature | Room Temperature | K | All experiments conducted at ambient conditions. |
| Primary NV Separation (d) | 3.9 | ”m | Distance between source (NVA) and target (NVB). |
| Hole Capture Cross Section (Ïh(Exp)) | ~3 x 10-11 | cm2 | Measured value at zero electric field (V=0). |
| NV Ionization/Recombination Time (Ï) | ~0.9 | ”s | Characteristic charge state cycling time under 520 nm illumination. |
| AC Switching Frequency (Minimum) | >10 | kHz | Frequency required to suppress space-charge potentials. |
| NV Implantation Energy | 20 | MeV | N+ ion implantation, resulting in defects ~10 ”m deep. |
| Monte Carlo Cutoff Energy (Ec) | 175 | meV | Corresponds to the optical phonon energy in diamond. |
| Diamond Relative Dielectric Constant (Δ) | 5.4 | N/A | Used for modeling Coulomb interaction (U). |
| NV Readout Wavelength | 594 | nm | Low-power laser used for single-shot charge state discrimination. |
- Sample Fabrication: Electronic grade diamond was implanted with 20 MeV N+ ions, followed by high-temperature annealing to create spatially-resolved NV centers, including pairs separated by distances ranging from 2.7 ”m to 8.6 ”m.
- Optical Setup: A home-built confocal microscope was used for addressing individual NV centers, employing 520 nm (ionization/injection), 594 nm (readout), and 632 nm lasers.
- Charge State Initialization: Both NV centers were preferentially initialized into the negatively charged state (NV-) using 520 nm illumination.
- Carrier Injection Protocol: The source NV (NVA) was continuously illuminated (520 nm) to induce repeated ionization and recombination cycles, generating a stream of free electrons and holes (h+).
- Electric Field Application: External electric fields (DC or AC) were applied via parallel surface electrodes, aligned with the line connecting the NV pair, using a fast MOSFET switch with rise/fall times of ~100 ns.
- Space-Charge Compensation (AC Protocol): To obtain reliable capture rates, the electric field was switched on and off at high frequencies (>10 kHz) during the photoionization pulse (50% duty cycle) to prevent the formation of metastable space-charge potentials.
- Capture Measurement: The unit-time hole capture probability was determined by measuring the bleaching rate (NV- to NV0 conversion) of the target NV (NVB) as a function of the applied AC electric field amplitude.
- Monte Carlo Modeling: Semi-classical simulations were performed using Newtonian equations of motion in 3D. Hole capture was modeled as a âcascadeâ process where the hole loses kinetic energy via inelastic acoustic and optical phonon scattering until its total energy falls below a cutoff (175 meV), leading to binding.
| Industry/Sector | Application/Product Relevance | Technical Benefit |
|---|
| Quantum Computing & QIP | Solid-state quantum bus realization; Spin qubit detection schemes. | Provides fundamental understanding of carrier dynamics required for communicating between remote solid-state qubits using spin-polarized carriers. |
| Quantum Sensing & Metrology | Nanoscale electrometry; Monitoring non-fluorescent defects (e.g., P1 centers). | Enables the use of NV centers as local probes to monitor charge state dynamics and trapping by adjacent, non-fluorescent defects, enhancing sensing capabilities. |
| Semiconductor Device Reliability | Single-photon sources (SPS) and optoelectronics. | Data on carrier recapture mechanisms helps mitigate charge instabilities responsible for emission spectrum fluctuations and reduced coherence in SPS devices. |
| High-Power/High-Frequency Electronics | Wide bandgap semiconductor devices (e.g., diamond, SiC). | Derives accurate, unscreened capture cross sections in pristine insulators, crucial for modeling device performance where high defect concentrations or screening effects are absent. |
| Advanced Materials Research | Investigating Rydberg-like states and bound excitons. | Results serve as a stepping stone for addressing fundamental questions regarding the stability and lifetime of transient bound states formed during carrier capture in high-purity crystals. |
View Original Abstract
Understanding carrier trapping in solids has proven key to semiconductor technologies, but observations thus far have relied on ensembles of point defects, where the impact of neighboring traps or carrier screening is often important. Here, we investigate the capture of photogenerated holes by an individual negatively charged nitrogen-vacancy (NV) center in diamond at room temperature. Using an externally gated potential to minimize space-charge effects, we find the capture probability under electric fields of variable sign and amplitude shows an asymmetric-bell-shaped response with maximum at zero voltage. To interpret these observations, we run semiclassical Monte Carlo simulations modeling carrier trapping through a cascade process of phonon emission and obtain electric-field-dependent capture probabilities in good agreement with experiment. Because the mechanisms at play are insensitive to the characteristics of the trap, we anticipate the capture cross sections we observeâlargely exceeding those derived from ensemble measurementsâmay also be present in materials platforms other than diamond.
- 2007 - Theory of Defects in Semiconductors [Crossref]
- 2018 - Dopants and Defects in Semiconductors [Crossref]