Photoluminescent n-type liquid organic semiconductor

Liquid 4,7-bis（1-decynl）-2,1,3-benzothiadiazole（DOBT） is found to exhibit good photoluminescence（PL） with high PL efficiency up to 17.8%. In particular, DOBT shows electron mobility of 5.2×10-6 cm2V-1s-1, demonstrating a promising n-type liquid semiconductor for optoelectronic application.     

Study on external-cavity semiconductor laser

In this paper, a narrow-band tunable external-cavity semiconductor laser with the Littman set-up is reported. The laser system consists of a semiconductor laser, a blazed grating and an external mirror. Its sideband suppression ratio over 20 dB was obtained. Conveniently tuning in wavelength region of 797.38 - 807.26 nm was achieved. The laser is operating in single frequency with narrow linewidth smaller than 0.06 nm. The output beam has good directional stability when tuned.     

Screening in a δ-doped semiconductor

The screening of an impurity in the quasi-two-dimensional (2D) electron gas in a δ-doped semiconductor structure is investigated. The screened impurity matrix elements are calculated and compared using three different approaches: the 2D random phase approximation (RPA), the corresponding 2D Thomas–Fermi theory and a quasi-three-dimensional (3D) Yukawa-like screening model. It is found that the 2D Thomas–Fermi theory differs from the RPA result, even in the limit of low q vectors, if more than one subband is occupied. This result is explained analytically by closely examining theq → 0 limit of the dielectric tensor. The 2D Thomas–Fermi theory is shown to represent a poor approximation to the RPA whereas the quasi-3D screening model agrees well with the RPA results for not too smallqvectors. Furthermore, this model reduces computing times by orders of magnitude in comparison with the RPA. Thus, our 3D screening model considerably simplifies the calculation of impurity scattering rates in the investigation of the electron mobility in a δ-doping layer.     

Acoustoelectric effect in semiconductor materials and devices

This paper reviews the studies on acoustoelectric effectin extrinsic semiconductor materials used in various scientific and othermeasurements.A historical review of earlier findings is given with specialreference to associated mechanisms.Acoustoelectric studies in solid statedevioes require further attention and the work done in this area is alsodiscussed.     

Optical power equalization using Fabry-Perot semiconductor optical amplifier

A novel scheme of optical power equalization based on Fabry-Perot semiconductor optical amplifier (FP-SOA) is proposed. Because of the gain characteristic of FP-SOA, real-time controlling mechanism according to input optical power is aborted in the scheme. The simulations show that 10-dB pulse peak power variation can be clamped in less than 1 dB. The influences of injecting current, pulse periods, and pulse width are discussed.     

Quantum interference effects in semiconductor–superconductor microjunctions

We investigate the quantum interference effects in quantum dots of a two-dimensional electron gas attached to a superconductor. When the dot size is comparable to the Fermi wavelength of an electron, transmission resonance shows up in the conductance as distinct peaks and dips. The coupling of electron-like and hole-like excitations by the Andreev reflection leads to a rich variety of behavior of the resonance, in particular, against the bias voltage. Enlarging the dot size, the transmission resonance evolves into conductance fluctuations. The low-magnetic-field conductance fluctuations are shown to be remarkably geometry-specific in comparison to those in the normal counterparts.     

Field-emission diodes based on semiconductor—polycrystalline diamond heterojunctions

A complex of electrophysical and technological studies of solid-state field-emission diodes is carried out. Emission comes from an array of nanometer objects near the semiconductor—polycrystalline diamond interface. The process route of the diode heterostructures includes the fabrication of nanometer masks and nanometer cone (tip) arrays, as well as plasma-assisted growth of polycrystalline diamond films on the surface of structures with nanometer cone arrays. In field-emission diodes thus formed, a current density as high as 20 A/cm² is achieved at a threshold of field emission from the nanotip arrays into the diamond of about 0.5 V.     

Mn–AlInN: a new diluted magnetic semiconductor

Mn ions have been incorporated into MOCVD grown Al_1−x In _x N/GaN thin films by ion implantation to achieve the room temperature ferromagnetism in the samples. Magnetic characterizations revealed the presence of two ferromagnetic transitions: one has Curie points at ∼260 K and the other above room temperature. In-diffusion of indium caused by the Mn implantation leads to the partition of AlInN epilayer into two diluted magnetic semiconductor sub-layers depending on the Mn concentration. The Curie temperature of 260 K is assigned to the layer having lower concentration, whereas T _c above room temperature is assumed to be associated to the layer having higher Mn concentration.     

II–VI semiconductor nanoparticles synthesized by laser ablation

Nanoparticles of the II–VI semiconductors CdTe, CdSe and ZnTe were synthesized by laser ablation (387 nm, 180 fs, 1 kHz, pulse energy of 7 μJ (fluence of 2 J/cm²)) of the target materials in methanol, de-ionized water and acetone. The nanoparticles size distributions follow log-normal functions with median diameters between about 6 and 11 nm for the several materials. The nanoparticles have the same crystalline structure as that of the corresponding bulk material and under the present conditions of ablation are rich in the higher volatility element of the two in the binary alloy and oxidized. Photoluminescence emission in the green-yellow (∼570 nm) was detected from CdSe nanoparticles.     

Atomically thin MoS₂: a new direct-gap semiconductor

The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS? monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10? compared with the bulk material.     

Spin ordering in semiconductor heterostructures with ferromagnetic δ layers

The magnetic properties of a magnetic-metal δ layer placed in a nonmagnetic nondegenerate semiconductor matrix are studied theoretically. The diffusion-induced spread of the δ layer, which is inevitable during δ doping, is taken into account, and a model is proposed in which this layer consists of a thin core enriched in metal atoms and a smeared periphery depleted in metal atoms. The exchange and potential scattering of carriers by the core causes confinement states in the form of two-dimensional spin-polarized sub-bands inside the energy gap of the semiconductor. The mechanism of the indirect exchange between impurity spins located in the strongly dilute peripheral region of the δ layer through partly filled confinement states is analyzed. In the case of a ferromagnetic core, impurity spins are oriented along (or opposite to) the core magnetization owing to carrier polarization on the confinement states. The magnetic configuration of impurity spins at the periphery of the δ layer is phenomenologically studied with allowance for the confinement mechanism of the interaction of impurity spins and the superexchange through the deep states in the semiconductor matrix.     

Quantized longitudinal exciton-polaritons in periodic metal–semiconductor nanostructures

We theoretically investigate the optical properties of one-dimensional photonic crystals composed of two alternating layers, namely a semiconductor film and a metallic one. The nonlocal optical response of the semiconductor is here described by using a resonant excitonic dielectric function, whereas the local response function of the metal film is modeled with Drude formula. We calculate optical spectra of the metal–semiconductor 1D photonic crystal for both s- and p-polarization geometries. In both cases the spectra exhibit a rich resonance structure due to the coupling of size-quantized excitons inside the semiconductor film with light. We show the difference between s- and p-polarization reflectivity as the angle of incidence is increased. In the p-polarization geometry, besides transverse exciton-polariton modes, longitudinal polarization waves are excited producing additional spectral resonances. The spectra become radically different when the frequency corresponding to the minimum of the first photonic pass-band is close to the exciton resonance, since such a frequency is distinct for s- and p-polarized modes. We also show how reflectivity spectra for both polarizations are modified with varying the metal filling fraction which controls the width of the gap below the lowest frequency band.     

Quasi-soliton generation in solid-state lasers with semiconductor saturable absorber

Recent advances in ultrafast, ultra-short solid-state lasers have resulted in sub-6 fs pulses generated directly from the cavity of Ti:sapphire lasers. The generation of extremely short pulses is possible due to the formation of a quasi-Schrodinger soliton. Our investigation is directed to the peculiarities of the transition between femtosecond to picosecond generation. We found that the above transition is accompanied by the threshold and hysteresis phenomena. On the basis of soliton perturbation theory, the numerical simulation studying two different experimental situations has been performed, the first situation corresponds to the study of the lasers field's parameters under variation of control parameters (dispersion or pump power), the second one is for continuous variation of control parameter within a single generation session. Physically it corresponds to not repeated laser session but the variation of control parameter when the pulse has formed already.     

Polarization-independent wavelength conversion using a single semiconductor optical amplifier

Polarization-independent wavelength conversion is demonstrated by using four-wave mixing (FWM) in a single semiconductor optical amplifier (SOA). In this scheme, all the incident fields are split into two orthogonal-polarized parts by polarizing beam splitters (PBS). Each of the two parts is then transmitted into one facet of the SOA and they are counter-propagating through the same amplifier. Wavelength conversion with the polarization sensitivity less than 1.3 dB is obtained over a range from 1510 to 1620 nm.     

Low-frequency fluctuation in multimode semiconductor laser subject to optical feedback

Dynamics of a semiconductor laser subject to moderate optical feedback operating in the low-frequency fluctuation regime is numerically investigated.Multimode Lang-Kobayashi(LK)equations show that the low-frequency intensity dropout including the total intensity and sub-modes intensity is accompanied by sudden dropout simultaneously,which is in good agreement with experimental observation.The power fluctuation is quite annoying in practical applications,therefore it becomes important to study the mech- anism of power fluctuation.It is also shown that many factors,such as spontaneous emission noise and feedback parameter,may influence power fluctuation larger than previously expected.     

A wire-form emitter metal–insulator–semiconductor tunnel junction

Physical effects arising due to change of configuration of a MIS system from planar to cylindrical, are theoretically analyzed. Attention is paid to the voltage partitioning and all the components of tunneling current. A simple simulation model is developed enabling prediction of the band diagram details and calculation of the currents. The trends expected with decreasing system radius are elucidated. Cylindrical geometry can be faced with when quantum wire is used as an electron emitter. Similar form may also be roughly attributed to an edge region of conventional MIS capacitors.     

Studies on optical dephasing of amorphous semiconductor with incoherent light

Dephasing in a-Si_(0.65)C_(0.35): H is observed by time-delayed four-wave mixing incoherent light. Results are in correspondance with consequences of disorder and localization on nonlinear optical response of the solid.     

Experimental study of mode characteristics for equilateral triangle semiconductor microcavities

Equilateral triangle semiconductor microcavities with tensile-strained InGaAsP multi-quantum-well as the active region are fabricated by the inductively coupled plasma (ICP) etching technique. The mode characteristics of the fabricated microcavities are investigated by photoluminescence, and enhanced peaks of the photoluminescence spectra corresponding to the fundamental transverse modes are observed for microcavities with side lengths of 5 and 10μm. The mode wavelength spacings measured experimentally coincide very well with those obtained by the theoretical formulae.     

Biochemistry and semiconductor electronics--the next big hit for silicon?

Two recent developments portend a new era for silicon electronics in biomedical applications. Firstly, highly specific chemical recognition and massively parallel sample preparation techniques are being combined with VLSI to make new kinds of analytical chips. Secondly, critical dimensions are beginning to approach the size of biomolecules, opening new pathways for physical interactions between molecules and semiconductor structures. Future generations of hybrid chemical-CMOS devices could revolutionize diagnosis and make personalized medicine cheap enough to become widespread.