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Quantum dots can be produced in a variety of material systems and geometries.
The simulations are performed with NEMO5 which can handle realistically extended quantum dot systems for research and exploration purposes.
The default simple geometries such as boxes, cylinders, pyramids, and ellipsoids enable educational users to explore confinement symmetries and absorption experiments in one conduction band.
Users can choose between simple single band effective mass model, two band effective mass model and 4 other tight binding models (sp3s* and sp3d5s* with and without spin).
3-D visualization depicts the 3-D confined wave functions. Optical transitions are computed and sorted into dark and light lines. Absorption curves are computed for different polarizations and orientations. Parameters such as incident light angle and polarization, Fermi level, or temperature can be scanned to analyze the effect of 3-D geometries on isotropic optical properties. The simulation is fully parallelized and depending on the device structure, the tool decides the computational resource to be used for the simulation. This tool is supported by variety of different materials:
- A First time user guide
- A general tutorial entitled "Quantum Dots" on the origin of quantum mechanics and the interpretation of quantum dots as artificial atoms.
- An introductory tutorial to the tool "Introduction to Quantum Dot Lab" with usage scenarios on state filling, light/dark absorption lines, and absorption coefficients.
- A homework / project assignment entitled "Homework Exercise on Quantum Dot Spectra, Absorption, and State Symmetry".
A topic page is available with homeworks/tests/real-life problems.
Upgrades from previous versions:
- Ver 1.1: Now users can select an effective mass of the quantum dot. Also the tool speed was a bit improved and there is a status bar indicating progress in the visualization preparation – which had been slow.
- Ver 1.1.1: The optical absorption lines are not as finely resolved and therefore do not demand such large file sizes. The default absorption line width was also increased by a factor of 10. Finally the number of allowed states was increased to 150.
- Ver 1.1.4: Added default values for effective mass for the different materials listed.
- Ver 2.0: The tool now runs NEMO 5 instead of NEMO 3D. This fixes a problem connected to the absolute position of energy levels. A 1s tight-binding band structure model is used which is equivalent to an effective-mass model. The optical matrix elements and absorption peaks are calculated slightly differently compared to the old tool. The GUI has been rearranged, allowing for the effective mass parameters to be set by the user. The tab for optical calculations has also been cleaned up. The performance of NEMO 5 is still undergoing optimizations.
- Ver 2.0.1/2: 4 digits of floating point is used in energy states plot. Fixed error when the different number of states is used. Several detailed description of input parameters is updated.
- Ver 2.1: Update to NEMO 5 r4228.
- Ver 3.0: Update to NEMO 5 r17881. The tool can now simulate both particle in a box problem and multilayer structures composed of substrate, wetting layer and a capping layer. Also, the users can now choose between a single band effective mass model, 2 band effective mass model and 10 band sp3d5s* tight binding simulation. The tool can submit jobs to clusters for large simulations.
- Ver 3.1: Update to NEMO 5 r19861. Added feature to simulate strain and local bandstructure.
- Ver 3.2: Significant feature updates:
- Scientific improvements:
- Four tight binding models with various degrees of sophistication are now enabled. These are the today's state-of-the-art sp3s* and sp3d5s* models with and without spin orbit coupling. As such these models cover 5, 10, and 20 orbitals resulting in 5, 10, and 20 band models.
- The sp3d5s* models use the strain parameterization for InAs & GaAs by Klimeck and Boykin
- The sp3s* models use a simple strain Harrison scaling rule where the users can modify the exponents.
- The simulation domains in the substrate and the lateral dimension can now be expanded appropriately to allow for the proper calculation of strain.
- The local bandstructure and strain distribution vertically through the quantum dot system is now plotted.
- Advanced control of algorithmic parameters for expert users (convergence parameters etc).
- Uncertainty quantification (UQ) enabled for a variety of design and simulation parameters.
- New single point outputs such as ground state, excited state, and bandgap energies open opportunities to use UQ for design.
- Update to NEMO 5 r24719.
- User interface and graphical features.
- Overall screen design rearranged and compacted to fit onto a smaller screen.
- 3D visualizations
- Electron and hole states are now displayed in separate panels.
- By default the electron and hole wavefunctions are now shown with the transparent view of the confining quantum dot and the wetting layer.
- Option to view the entire simulation domain with the wavefunctions.
- Option to view the wavefunctions without any shaded confinement regions.
- option to view the various simulation domains.
- User controlled resolution of 3D images.
- Local bandstructure and strain profiles vertically through the quantum dot system can be plotted.
- Fermi levels are specified separately for the simple effective mass models and the more complex multiband models.
- Single or multi-point outputs of electron ground and excited states, bandgap, and all eigen energies.
- Substantially improved messaging from remote execution for large scale simulations. Separate error reporting for the remote tool execution and the submission process. Control of messaging level of NEMO5.
- Remote execution
- New scheduling mechanism into dedicated remote computing resource. The status of the dedicated and shared resource queue is checked before remote job submission.
- If the dedicated resources are available a greedy algorithm will submit jobs minimizing the required parallel compute times. As the queue fills up less greedy parallel execution will result in longer compute times, but larger numbers of users to participate. Anticipated parallel compute times are set for 15, 25, 35, and 45 minute targets.
- Once the queues are full the algorithm will fall back onto the standard nanoHUB submission process.
- Advanced users van view the queue and make a decision on queue submission, parallel core count and simulation time.
- Scientific improvements:
- Ver 3.2.1: Significant feature updates:
- The pyramidal quantum dot is now the default shape, instaead of the cuboid
- Energy differences between the electron ground state and the next two excited states are explicitly added as two individual scattered output numbers. That allows an uncertainty quantification (UQ) analysis of these energies as a function of geometries. In an UQ run ONLY eigen energies and energy differences are plotted. They can be explored as response functions to surrogate models.
- Ver 3.2.2: Port from cluster computer Brown to Negishi:
- No other functional changes. Brown is retired and Negishi has 128 cores per CPU.
Quantum Dot Lab version 1.x ran NEMO-3D. Starting from version 2.0, the underlying engine is NEMO 5, a code under development in the research group of Gerhard Klimeck. NEMO 5 is a nanoelectronics device simulator containing a variety of different material and geometry models. Features include the construction of atomistic grids of varying crystal structures, multiband Schroedinger-Poisson simulations, and user-friendly input/output.
Prasad Sarangapani: Development of Quantum Dot Lab 3.0.
Jim Fonseca: Student supervision
Daniel F Mejia:Visualization of electron wavefunctions.
Andrew Roche:Rappture interface, simulation timing
Woody Gilberton:Rappture interface
Tarek Ameen:Local bandstructure
Hesam Ilatikhameneh: Strain
James Charles:Lanczos eigenfunctions
Lars Bjaalie: Integration of NEMO 5 with Quantum Dot Lab.
Matteo Mannino, David Ebert, Michael McLennan: Initial version of Quantum Dot Lab (<2.0).
Sebastian Steiger, Michael Povolotskyi, Tillmann Kubis, Hong-Hyun Park: NEMO 5 core development team.
Gerhard Klimeck: General supervision.
Gerhard Klimeck: Revision 3.2.
Cite this work
Researchers should cite this work as follows:
- "Building and Deploying Community Nanotechnology Software Tools on nanoHUB.org and Atomistic simulations of multimillion-atom quantum dot nanostructures", Gerhard Klimeck, Marek Korkusinski, Haiying Xu, Seungwon Lee, Sebastien Goasguen and Faisal Saied, Proceedings of the 5th IEEE Conference on Nanotechnology, 2: pg. 807, 07 (2005)
Prasad Sarangapani, James Fonseca, Daniel F Mejia, James Charles, Woody Gilbertson, Tarek Ahmed Ameen, Hesameddin Ilatikhameneh, Andrew Roché, Lars Bjaalie, Sebastian Steiger, David Ebert, Matteo Mannino, Hong-Hyun Park, Tillmann Christoph Kubis, Michael Povolotskyi, Michael McLennan, Gerhard Klimeck (2024), "Quantum Dot Lab," https://nanohub.org/resources/qdot. (DOI: 10.21981/CPJ9-3Q95).