Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

Temperature dependent photoluminescence from lead sulfide nanosheets and nanocubes.

Abstract: We studied temperature dependent photoluminescence (PL) spectra in the mid-infrared range from lead sulfide (PbS) nanosheets with an average thickness of 25 nm and nanocubes grown by solvothermal and hydrothermal methods. Distinct bandedge PL emission was observed in the whole temperature range between 10 and 300 K, indicating the high optical quality of these nanostructures. The PL peak of the nanosheets was found at 0.326 eV at 10 K, about 40 meV higher than that of bulk PbS due to the quantum confinement effect, whereas no confinement effect was observed for the nanocubes. We also demonstrate that the absorption edges of the nanocubes and nanosheets in the transmission spectra agree very well with their fundamental bandgap.

Luminescent nanoclusters array fabricated by pulsed laser beam irradiation

Abstract: Ordered luminescent nanoclusters array in the form of grating structures are fabricated on silicon (1 0 0) surface by Q-switched Nd:YAG laser beam irradiation of second harmonic wavelength (532 nm) in vacuum. Blue-green photoluminescence (PL) spectrum from the ordered nanoclusters array exhibits two asymmetrical peaks at 2.58 eV and 2.88 eV in the blue-green region corresponding to the bimodal distribution of nano size clusters. The size of the nanoclusters is estimated from the three dimensional quantum-confined model incorporating Gaussian size distribution. When subjected to rapid thermal annealing at 710 °C for 10 min in N2 atmosphere there is an enhancement of the PL intensity without any change in the peak emission energy and broadening suggesting that the origin of PL is related to quantum confinement effect in Si nanocrystallite. The surface morphology of the irradiated surface varies considerable with the number of laser shots, laser fluence and ambient conditions.

Size-Dependent and Enhanced Photovoltaic Performance of Solar Cells Based on Si Quantum Dots

Abstract: Recently, extensive studies have focused on exploring a variety of silicon (Si) nanostructures among which Si quantum dots (Si QDs) may be applied in all Si tandem solar cells (TSCs) for the time to come. By virtue of its size tunability, the optical bandgap of Si QDs is capable of matching solar spectra in a broad range and thus improving spectral response. In the present work, size-controllable Si QDs are successfully obtained through the formation of Si QDs/SiC multilayers (MLs). According to the optical absorption measurement, the bandgap of Si QDs/SiC MLs shows a red shift to the region of long wavelength when the size of dots increases, well conforming to quantum confinement effect (QCE). Additionally, heterojunction solar cells (HSCs) based on Si QDs/SiC MLs of various sizes are presented and studied, which demonstrates the strong dependence of photovoltaic performance on the size of Si QDs. The measurement of external quantum efficiency (EQE) reveals the contribution of Si QDs to the response and absorption in the ultraviolet–visible (UV-Vis) light range. Furthermore, Si QDs/SiC MLs-based solar cell shows the best power conversion efficiency (PCE) of 10.15% by using nano-patterned Si light trapping substrates.

Phase transition and topological transistors based on monolayer Na3Bi nanoribbons.

Abstract: Recently, a topological-to-trivial insulator quantum-phase transition induced by an electric field has been experimentally reported in monolayer (ML) and bilayer (BL) Na3Bi. A narrow ML/BL Na3Bi nanoribbon is necessary to fabricate a high-performance topological transistor. By using the density functional theory method, we found that wider ML Na3Bi nanoribbons (>7 nm) are topological insulators, featured by insulating bulk states and dissipationless metallic edge states. However, a bandgap is opened for extremely narrow ML Na3Bi nanoribbons (<4 nm) due to the quantum confinement effect, and its size increases with the decrease in width. In the topological insulating ML Na3Bi nanoribbons, a bandgap is opened in the metallic edge states under an external displacement electric field, with strength (∼1.0 V A−1) much smaller than the reopened displacement electric field in ML Na3Bi (3 V A−1). An ultrashort ML Na3Bi zigzag nanoribbon topological transistor switched by the electrical field was calculated using first-principles quantum transport simulation. It shows an on/off current/conductance ratio of 4–71 and a large on-state current of 1090 μA μm−1. Therefore, a proof of the concept of topological transistors is presented.

Homogeneous Width of Confined Excitons in Quantum Dots — Experimental

Abstract: A quantum dot has quantized energy levels that show a size-dependent blue-shift as a result of the quantum confinement effect. The quantized levels have been generally believed to be as sharp as the 5-function, reflecting its atomic character and size. Other inhomogeneities in the ensemble of quantum dots are considered to make the optical spectrum of the levels broad. However, this consideration is oversimplified. As a result of unique dephasing mechanisms in quantum dots, the homogeneous width of quantum dots is not so sharp as the σ-function, but is found to be finite and is sometimes broader than that of the bulk crystals. It is given by the inverse of dephasing time consisting of radiative lifetime, impurity or defect scattering time, surface or interface scattering time, phonon scattering time, and carrier-carrier scattering time at the excited states. Because electrons, excitons, and phonons are size-quantized in quantum dots, the electron-phonon and exciton-phonon interactions in quantum dots are unique. Temperature dependence of the homogeneous width reflects the unique temperature-dependent dephasing mechanisms of quantum states by phonons; their study is very important. Therefore the homogeneous linewidth of the optical spectra of quantum dots is one of the most important characters of quantum dots.