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InPBi exhibits broad and strong photoluminescence at room temperature, and is a potential candidate for fabricating super-luminescence diodes applied in optical coherence tomography. In this paper, the strained InPBi quantum dot (QD) embedded in the AlGaAs barrier on a GaAs platform is proposed to enhance the light emission efficiency and further broaden the photoluminescence spectrum. The finite element method is used to calculate the strain distribution, band alignment and confined levels of InPBi QDs. The carrier recombinations between the ground states and the deep levels are systematically investigated. A high Bi content and a flat QD shape are found preferable for fabricating super-luminescence diodes with high efficiency and a broad emission spectrum.

The surface characteristics of ZnO were synthetically optimized by a self-designed simultaneous etching and W-doping hydrothermal method utilizing as-prepared ZnO nanorod (NR) array films as the template. Benefiting from the etching and regrowth process and the different structural stabilities of the various faces of ZnO NRs, the uniquely etched and W-doped ZnO (EWZ) nanotube (NT) array films with larger surface area, more active sites and better energy band structure were used to improve the photoelectrochemical (PEC) performance and the loading quality of CdS quantum dots (QDs). On the basis of their better surface characteristics, the CdS QDs were uniformly loaded on EWZ NT array film with a good coverage ratio and interface connection; this effectively improved the light-harvesting ability, charge transportation and separation as well as charge injection efficiency during the PEC reaction. Therefore, all the CdS QD-sensitized EWZ NT array films exhibited significantly enhanced PEC performance. The CdS/EWZ-7 composite films exhibited the optimal photocurrent density with a value of 12 mAâ‹...cmâˆ'2, 2.5 times higher than that of conventional CdS/ZnO-7 composite films under the same sensitization times with CdS QDs. The corresponding etching and optimizing mechanisms were also discussed. [ABSTRACT FROM AUTHOR]

In this article, a long-wave infrared InAs/GaAs sub-monolayer quantum dot quantum cascade photodetector (SML QD-QCD) grown on GaAs substrate is demonstrated. Temperature- and excitation-dependent photoluminescence measurements are used to study the optical properties of the quantum dot active region, which reveal energetically hybrid ground states between the InAs quantum dot and InGaAs quantum well due to the possible inter-mixing of In and Ga atoms during growth process. The device covers a spectral region from 6.5 to 9 μm. At 77 K, a peak responsivity of 7.5 mA/W is found at 8.3 μm (0 V) and a zero-bias differential-resistance-area (R0A) product of 9008 Ω·cm2 is obtained. The white noise-limited detectivity is 6.5 × 109 cm·Hz1/2/W. These results encourage the SML QD-QCD as a strong competitor for long-wave infrared imaging applications that require normal incidence and low power dissipation. [ABSTRACT FROM AUTHOR]

A germanium (Ge) or germanium-on-silicon (Ge-on-Si) substrate is an attractive yet not well-studied platform for developing long-wave infrared photonics devices such as lasers and photodetectors. In this paper, we report a long-wave infrared quantum cascade photodetector grown on the Ge substrate with a submonolayer InAs/GaAs quantum dot as the infrared absorber. At 77 K under zero bias, the detector shows a differential-resistance area ( R 0 A) product of 298.7 Ω·cm2. The normal-incident peak responsivity is 0.56 mA/W observed at 8.3 μm, corresponding to a Johnson noise limited detectivity of 1.5 × 108 cm·Hz1/2/W. In addition, the effect of the periodic stage number of active regions on device's performance is discussed in detail. The device characteristics presented in this work demonstrate the potential for monolithic integration of this quantum cascade detector with the Ge or Ge-on-Si substrate for large-scale, cost-effective sensing and imaging applications. [ABSTRACT FROM AUTHOR]

Highly tensile-strained Ge quantum dots (TS-Ge-QDs) emitting structures with different size were successfully grown on InP substrates by molecular beam epitaxy. Dislocation-free TS-Ge-QDs were observed by transmission electron microscopy. Finite element modeling indicates a maximum tensile strain of 4.5% in the Ge QDs, which is much larger than the required strain to achieve direct band gap conversion of Ge based on theoretical prediction. Photoluminescence (PL) from a direct band-gap-like transition of TS-Ge-QDs with a peak energy of 0.796 eV was achieved and confirmed by the etch depth-dependent PL, temperature-dependent PL, and excitation-power-dependent PL. In addition, a strong defect-related peak of 1 eV was observed at room temperature. The band structure of the TS-Ge-QDs emitting structures was calculated to support the experimental results of PL spectra. Achieving PL from direct band-gap-like transitions of TS-Ge-QDs provides encouraging evidence of this promising highly tensile strained semiconductor-nanostructure-based platform for future photonics applications such as integrated light sources. [ABSTRACT FROM AUTHOR]

The binding energy of a hydrogenic donor impurity in a zinc-blende GaN/AlGaN cylindrical quantum dot (QD) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position and QD size. The external electric field induces an asymmetrical distribution of the donor binding energy with respect to the center of the QD. The maximum of the donor binding energy is shifted from the center of the QD. The degenerating energy levels for symmetrical positions with respect to the center of QD are also split. The splitting increases with the increase in QD height while the splitting increases up to a maximum and then decreases with the increase in QD radius. In the presence of the external electric field, the donor binding energy is insensitive to dot height when the impurity is located at the left side of the QD with large dot height. In addition, Stark shift dependence on hydrogenic impurity position is calculated. [ABSTRACT FROM AUTHOR]

Using a novel growth mechanism on patterned high-index GaAs (311)A substrates we have developed a new concept to fabricate quantum wires and quantum dots as well as coupled quantum wire–dot arrays by molecular beam epitaxy. The combination of self-organized growth with lithographic patterning and the assistance of atomic hydrogen produces these quasi-planar lateral nanostructure arrays with unprecedented uniformity in size and composition and with controlled positioning on the wafer. The sought for one- and zero-dimensional nature of these quantum wire and quantum dot arrays manifests itself in the superior optical properties. To functionalize our lateral semiconductor quantum wire and quantum dot arrays with the properties of magnetic thin films, epitaxial Fe layers have been grown on GaAs (311)A. Defect free Fe layers are obtained on As-saturated GaAs surfaces. The large electrical conductivity of thin Fe layers indicates reduced Fe–GaAs interface compound formation. An unusual in-plane spontaneous Hall-effect is observed in these epitaxial Fe layers of reduced symmetry. [Copyright &y& Elsevier]

We report on a three-colour InAs/InP(100) quantum dot laser under continuous wave mode at an operation temperature of 20degC. Three lasing peaks are observed simultaneously, the high-energy peak undergoes continuous blueshift, while the splitting energy gap between the low-energy peaks is somewhat fixed as the injection current increases. The maximum output power from one facet without coating is more than 34 mW with a slope efficiency of 102 mW/A just above the threshold current. Three peaks of differential efficiency of output power are observed, just corresponding to each peak in lasing spectra, respectively. At the same time, the far-field distribution shows only a single transverse mode over the full range of injection current. [ABSTRACT FROM AUTHOR]

Abstract: To study the characteristics of quantum-dot semiconductor optical amplifiers (QD-SOA), a refined sectionalized method is developed and utilized to solve the rate equations for the first time based on the three-level model of QD-SOA. The calculation results prove that the operation speed of refined sectionalized method is about twice as fast as that of conventional sectionalized method in the same precision. In addition, the injection current density of each section can be dynamically set depending on the input optical power to keep high gain or prevent its declination. [Copyright &y& Elsevier]

Abstract: The I–V characteristics of an InAs/GaAs quantum dot (QD) laser diode have been investigated under both the high and low input current conditions. Under the low current condition, the I–V curve obeys the Shockley equation, from which the forbidden energy gap of the junction can be derived. On the other hand, in the high current range, the I–V characteristics violate the Shockley equation and the device tends to operate as a resistance. In addition, the I–V curve can be used to fit the temperature coefficient of the forward voltage, which is a critical parameter for determining the junction temperature of the laser diode. [Copyright &y& Elsevier]

Abstract: Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/Al x Ga1− x N spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated. [Copyright &y& Elsevier]