The poor radiative efficiency in quantum-box luminescence is tentatively explained as an intrinsic effect rather than the usually invoked effect of etch damages From the recently calculated decreased relaxation rate in zero-dimensional (0D) systems under 100\char21{}200-nm lateral quantization, we propose that electrons captured from the barriers in the upper levels of quantum boxes are retained in their cascade to the fundamental states for more than nanoseconds Due to the mutual orthogonality of quantum states in a box, no luminescence, or much less than in 2D or 3D, can be obtained from these stored electrons with reasonable assumptions for the hole population Magnetic-confinement experiments in quantum-well lasers support our conclusion A realistic model at low temperature describes more quantitatively the observed strong decay of the radiative efficiency in quantum boxes and pseudowires with decreased lateral dimensions

Intrinsic mechanism for the poor luminescence properties of quantum-box systems

Metallic cavities can confine light to volumes with dimensions considerably smaller than the wavelength of light. It is commonly believed, however, that the high losses in metals are prohibitive for laser operation in small metallic cavities. Here we report for the first time laser operation in an electrically pumped metallic-coated nanocavity formed by a semiconductor heterostructure encapsulated in a thin gold film. The demonstrated lasers show a low threshold current and their dimensions are smaller than the smallest electrically pumped lasers reported so far. With dimensions comparable to state-of-the-art electronic transistors and operating at low power and high speed, they are a strong contender as basic elements in digital photonic very large-scale integration. Furthermore we demonstrate that metallic-coated nanocavities with modal volumes smaller than dielectric cavities can have moderate quality factors.

Lasing in metallic-coated nanocavities

We present results on photoexcited carrier lifetimes in few-layer transition metal dichalcogenide MoS2 using nondegenerate ultrafast optical pump–probe technique. Our results show a sharp increase of the carrier lifetimes with the number of layers in the sample. Carrier lifetimes increase from few tens of picoseconds in monolayer samples to more than a nanosecond in 10-layer samples. The inverse carrier lifetime was found to scale according to the probability of the carriers being present at the surface layers, as given by the carrier wave function in few layer samples, which can be treated as quantum wells. The carrier lifetimes were found to be largely independent of the temperature, and the inverse carrier lifetimes scaled linearly with the photoexcited carrier density. These observations are consistent with defect-assisted carrier recombination, in which the capture of electrons and holes by defects occurs via Auger scatterings. Our results suggest that carrier lifetimes in few-layer samples are surfa...

https://people.ece.cornell.edu/rana/papers/paper43.pdf

Surface Recombination Limited Lifetimes of Photoexcited Carriers in Few-Layer Transition Metal Dichalcogenide MoS2

Metallic-Cavity lasers or plasmonic nanolasers of sub-wavelength sizes have attracted great attentions in recent years, with the ultimate goal of achieving continuous wave (CW), room temperature (RT) operation under electrical injection. Despite great efforts, a conclusive and convincing demonstration of this goal has proven challenging. By overcoming several fabrication challenges imposed by the stringent requirement of such small scale devices, we were finally able to achieve this ultimate goal. Our metallic nanolaser with a cavity volume of 0.67{\lambda}3 ({\lambda}=1591 nm) shows a linewidth of 0.5 nm at RT, which corresponds to a Q-value of 3182 compared to 235 of the cavity Q, the highest Q under lasing condition for RT CW operation of any sub-wavelength laser. Such record performance provides convincing evidences of the feasibility of RT CW metallic nanolasers, thus opening a wide range of practical possibilities of novel nanophotonic devices based on metal-semiconductor structures.

Record Performance of Electrical Injection Sub-wavelength Metallic-Cavity Semiconductor Lasers at Room Temperature

The objective of this review article is to give an overview of the current state-of-the-art of photoluminescence (PL) spectroscopy as a characterization tool in the study of semiconductors. A detailed description of all of the PL spectroscopic techniques will be given together with examples from the literature of their use. These examples will be the primary tool used to convey the essential aspects and usefulness of the variety of PL techniques discussed throughout this review. The primary examples of semiconductor materials examined with these techniques will be of the prototypical direct-gap and indirect-gap semiconductors, gallium arsenide and silicon, respectively. Additionally, PL characterization of structures with lower dimensionality (quantum wells, superlattices, quantum wires, and quantum dots) will be shown. This article will not cover the history of this type of spectroscopy, inelastic light scattering, infrared spectroscopy, or reflectance, etc. The focus is intended to be experimental in nature, and will be supplemented by theory where appropriate and necessary. There are several fine review articles and books dealing with the subject of photoluminescence, and radiative recombination in general, and this article is only intended to supplement these sources.

Photoluminescence spectroscopy of crystalline semiconductors

We have investigated the lateral width (Lx) dependence of the quantum efficiency of the excitonic recombination in etched InGaAs/InP wires (40 nm≤Lx≤5 μm). The analysis of data obtained at different temperatures implies that the intensity decay observed for narrow wires is due to the formation of an optically inactive (‘‘dead’’) layer and due to surface recombination.

Impact of sidewall recombination on the quantum efficiency of dry etched InGaAs/InP semiconductor wires

We have fabricated GaAs/GaAlAs quantum wires with widths between 220 and 40 nm by high‐dose (2×1014 cm−2) Ga implantation in a locally masked single quantum well structure. The width dependence of the emission energies indicates a steep 1D confinement determined by the lateral straggling of the implanted Ga. The external quantum efficiency of the wires increases strongly with decreasing mask width due to significant carrier capture from the lateral barrier.

Carrier capture in intermixed quantum wires with sharp lateral confinement

Buried GaAs/AlGaAs quantum wires were prepared by Al0.2Ga0.8As overgrowth of deep etched wires defined by high‐resolution electron beam lithography and dry etching. The overgrown wires show a dramatic decrease of the optically inactive sidewall layer compared to open wires. For wires with a lateral dimension Lx=50 nm we observe a spectral shift to higher energies of the excitonic emission, in good agreement with calculations of the two‐dimensional confinement effects.

Lateral quantization induced emission energy shift of buried GaAs/AlGaAs quantum wires

Chloromethylated poly‐α‐methylstyrene negative resist was investigated for its suitability in the fabrication of nanometer structures for optical studies. Investigating the photoluminescence efficiency of etched GaAs/AlGaAs wires we find a steep decrease with decreasing wire width, whereas for InGaAs/InP the decrease is much smaller. The difference in the behavior of the material systems can be explained by the effectiveness of surface recombination.

Nanometer lithography for III–V semiconductor wires using chloromethylated poly‐α‐methylstyrene resist

Time-resolved investigations on the photoluminescence of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wires as a function of the wire width and the potential well depth indicate a reduction of the energy relaxation in quasi-one-dimensional (1D) systems. The systematic change of the wire width and potential well depth of the quantum wires with mask widths down to 40 nm were realized by ion-implantation-induced intermixing of quantum wells. Lifetime measurements on the high-energy side of the quantum wire emission yield increased decay times for the smallest wires. This is consistent with our observation of increased carrier temperatures and slowed cooling in the quantum wires with increasing carrier confinement. We explain the reduction of the relaxation with the decreased possibility for the scattering particles to fulfill both energy and momentum relaxation in wires with gradually increasing 1D behavior.

Carrier relaxation in intermixed GaAs/AlxGa1-xAs quantum wires

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