The subject of this paper is microlasers with the emission spectra determined by the whispering gallery modes. Owing to the total internal reflection of light on the sidewalls, a high Q-factor is ...achieved until the diameter is comparable to the wavelength. The light emission predominantly occurs in the plane of the structure, which facilitates the microlaser integration with other elements. We focus on microdisk lasers with various types of the In(Ga)As quantum dots (QDs). Deep localization of charge carriers in spatially separated regions suppresses the lateral diffusion and makes it possible to overcome the undesirable effect of non-radiative recombination in deep mesas. Thus, using conventional epitaxial structures and relatively simple post-growth processing methods, it is possible to realize small microlasers capable of operating without temperature stabilization at elevated temperatures. The low sensitivity of QDs to epitaxial and manufacturing defects allows fabricating microlasers using III-V heterostructures grown on silicon.
Abstract In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion ...beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 μ m diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.
The results of studying the optical properties of InGaAs quantum dots are presented. Single-layer InGaAs quantum dots with a height of 5.3, 3.6 and 2.6 monolayers, as well as three-stacked layers of ...tunnel-uncoupled quantum dots with a height of 2.6 monolayers were formed by molecular-beam epitaxy according to the Stransky–Krastanov mechanism on GaAs substrates, using the partial capping and annealing technique. A decrease in the size of quantum dots makes it possible to carry out a blueshift of the photoluminescence spectrum maximum from 1200 to 1090 nm, and an increase in the number of QD layers makes it possible to compensate for the decrease in the peak intensity. It is shown that this type of quantum dots is suitable for creating the lasers active regions with a vertical microcavity for neuromorphic computing.
Gain saturation in a semiconductor optical amplifier with an array of quantum dots is studied analytically and by numerical simulation on the basis of an analysis of rate equations. It is shown that, ...at a moderate injection level, the saturation power increases in proportion to the current density, and then reaches its maximum value, limited by the rate of carrier delivery to the ground state and by the number of quantum dots interacting with photons. Expressions are proposed that allow explicit description of the dependence of the saturation power on current and its relationship with the internal parameters of the active region.
We demonstrate a record low threshold current density of 250 A/cm
2
in a quantum dot microdisk laser with a 31-μm diameter operating at room temperature in continuous wave regime without temperature ...stabilization. This low threshold current density is very close to the transparency current density estimated in broad-area edge-emitting lasers made of the same epitaxial wafer.
Rate equations are used to analyze the characteristics of a tandem device consisting of a laser diode and a semiconductor optical amplifier made of a single heterostructure with quantum dots. The ...optimal value of the current-distribution coefficient between the amplifier and the laser, as well as the optimal cavity length that provides the highest output power of the tandem device are determined. It is shown that the use of the tandem device allows, at the same total consumed current, a significant (more than 4 times for 1 A) increase in the power emitted through the ground-state optical transition in comparison with that achievable with a laser diode solely being limited by the onset of lasing through the excited-state optical transition.
Analytical expressions are presented, and, through them, the analysis of component parts of the electrical resistance of injection microdisk lasers is carried out depending on the size of the ...microdisk resonator, parameters of the substrate, and configuration of the contact to it.
The linewidth enhancement factor (LEF) of an InAs/InGaAs quantum dot Fabry-Pérot laser in a wide wavelength range from 1110 to 1300 nm, including ground state (GS) and exited state (ES) bands, is ...studied. LEF spectra were derived from amplified spontaneous emission spectra measured below the threshold in the pulse regime. The ES optical transition is characterised by significantly lower values of the LEF (≤0.54) as compared to the GS (≥1.21). Moreover, a zero LEF is observed within the ES spectral band. At sufficiently high currents, a near-zero LEF (|α| ≤ 0.1) is achieved in a wide spectral interval from 1146 to 1175 nm, in which the optical gain is not less than 9 cm−1.
Abstract
We demonstrate a new technique to fabricate silver dendritic structures in a subsurface glass layer based on electrolysis of silver-enriched glass. Chemical etching of glass in water diluted ...HF allows “opening” of the dendrites for their characterization, which makes possible their use for Surface-enhanced Raman scattering. The structure and morphology of the dendrites were characterized using atomic force and scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It was demonstrated that the surface morphology of the formed structures depends on the electric charge passed through the sample during the electrolysis and the duration of the chemical etching. The presented method does not require expensive equipment and materials and allows one to form silver nanostructures of a prescribed pattern.
The study concerns the issue of how the morphological characteristics and optical properties of morphologically branched InGaN nanostructures grown on the Si(111) surface by molecular-beam epitaxy ...depend on the substrate temperature. It is shown that, as the substrate temperature is elevated, the height of InGaN nanocolumns formed at the initial stage of growth increases. In addition, an increase in the growth temperature of InGaN nanostructures yields an increase in the intensity of the photoluminescence spectra of such structures, and the dependences of the integrated photoluminescence intensity on the excitation power density are linear. These facts suggest that the structures offer promise for optical applications, specifically, for the creation of white light-emitting diodes on the basis of a unified material.
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