Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials.

We report long-wavelength photoluminescence emission (∼1.6–1.7μm) from self-organized InAs surface quantum dots (SQDs) grown on GaAs substrate without any capping layers. Photoluminescence (PL) properties of these quantum dots (QDs) are strongly affected by the surface states and strain relaxation mechanism. Compared to the case of capped InAs QDs, a large redshift of about 466nm observed in the PL spectrum of SQDs can be attributed to the strain relaxation and the strong coupling of the confined states with the surface states. The PL properties of these SQDs can also be influenced by the presence of quasi-infinite surface potential.

Modeling of transitions in Mn 2+ doped ZnS nanocrystals and predicting reduced lasing threshold current density and enhanced electro-optic effects in ZnCdSe-ZnMgSSe and InGaN-AlGaN pseudomorphic quantum dots Using photoluminescence and Raman scattering, we have studied the optical properties of Mn-doped ZnS nanocrystallites prepared by a microemulsion-hydrothermal method. The PL spectrum shows two distinct peaks in the blue-green region. The PL peak from the nanoparticles, in the region 400-480 nm ͑3.1-2.6 eV͒, shifts toward the lower energy with decreasing excitation intensity, which shows that the luminescence originates from the donor-acceptor pair recombination. Such self-activated luminescence could involve the Zn vacancies and Mn acceptors. Micro-Raman scattering measurements on these nanostructured ZnS:Mn crystallites show a low-frequency wing at 315 cm Ϫ1 besides the characteristic first-order longitudinal optical phonon at 349 cm Ϫ1 . The transverse optical phonon from these nanocrystallites at 269 cm Ϫ1 along with a much weaker vibrational mode near 220 cm Ϫ1 was also observed.

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Two-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe2 p–i–n homojunction fabricated directly on a silicon photonic crystal (PC) waveguide, which enables on-chip photodetection with ultralow dark current, high responsivity, and fast response speed. The adopted silicon PC waveguide is electrically split into two individual back gates to selectively dope the top regions of the MoTe2 channel in p- or n-types. High-quality reconfigurable MoTe2 (p–i–n, n–i–p, n–i–n, p–i–p) homojunctions are realized successfully, presenting rectification behaviors with ideality factors approaching 1.0 and ultralow dark currents less than 90 pA. Waveguide-assisted MoTe2 absorption promises a sensitive photodetection in the telecommunication O-band from 1260 to 1340 nm, though it is close to MoTe2’s absorption band-edge. A competitive photoresponsivity of 0.4 A/W is realized with a light on/off current ratio exceeding 104 and a record-high normalized photocurrent-to-dark-current ratio of 106 mW–1. The ultrasmall capacitance of p–i–n homojunction and high carrier mobility of MoTe2 promise a high dynamic response bandwidth close to 34.0 GHz. The proposed device geometry has the advantages of employing a silicon PC waveguide as the back gates to build a 2D material p–i–n homojunction directly and simultaneously to enhance light–2D material interaction. It provides a potential pathway to develop 2D material-based photodetectors, laser diodes, and electro-optic modulators on silicon photonic chips.

The authors investigated the synthesis of GaIn(N)As∕Ga(N)As multiple quantum wells by molecular beam epitaxy. Introducing N into the GaInAs appears to suppress the incorporation of In as indicated by reflective high-energy electron diffraction (RHEED). This effect is mainly due to the N-induced enhancement of In surface segregation at the growth front and is evidenced by the increasing damping rate of RHEED oscillations with N incorporation. The N-induced enhancement of In segregation in the GaInNAs quantum wells is confirmed by secondary-ion-mass spectroscopy and high-resolution x-ray diffractions, and its origin is discussed.

The authors report the effect of growth temperature and monolayer coverage on areal density and photoluminescence spectral width of InAs quantum dot ͑QD͒. Areal density and spectral width were found to be strongly dependent on growth temperature and monolayer coverage, respectively. Upon proper tuning, both high areal density and large photoluminescence spectral width were obtained. Areal density of 1.5ϫ 10 11 cm −2 is four times higher than those previously reported, while spectral width of 136 nm is the broadest spectral width obtained without any forms of band gap engineering. These results will contribute to an improvement in the performance of QD superluminescent diode.

Self-organized InP quantum dots having a staggered band lineup (type II) are formed in a GaAs matrix by metalorganic chemical vapor deposition. Strong photoluminescence centered at 986 nm is observed for the sample of InP grown at 490 °C, which can be attributed to radiative recombination of zero-dimensional (0D) electrons located in the InP dots and holes located in the surrounding regions. The indirect recombination of photogenerated carriers has been confirmed by the measurement of luminescence at different excitation densities and temperatures. If the InP is grown at 600 °C, experimental results show that a thicker and much smoother wetting layer is formed which results in much stronger and narrower luminescence located at 875 nm. In addition, state filling of the 0D electrons is also observed for the type-II quantum dots.