Semiconductor Physics

most susceptible to the impact of pollution aerosols on their albedo (27). However, the findings here suggest that this susceptibility does not translate into large sensitivity to anthropogenic land-based aerosols as currently believed, for two reasons: (i) Aerosols in a cloudy marine boundary layer are deposited quickly by cloud processes; and (ii) when pollution aerosols manage to interact with clouds over the sea, the sea salt reduces the supersaturation and hence the droplet concentrations and cloud albedo. These are likely causes for the larger cloud drop r eff for the same aerosol index over the ocean as compared to land (28), recently observed by satellite, which has been unexplained until now.

pi-Conjugated molecular materials with fused rings are the focus of considerable interest in the emerging area of organic electronics, since the combination of excellent charge carrier mobility and high stability may lead to their practical applications. This tutorial review discusses the synthesis, properties and applications of pi-conjugated organic semiconducting materials, especially those with fused rings. The achievements to date, the remaining problems and challenges, and the key research that needs to be done in the near future are all discussed.

Typical Raman spectra of transition-metal dichalcogenides (TMDs) display two prominent peaks, E 2g and A 1g , that are well separated from each other. We find that these modes are degenerate in bulk WSe 2 yielding one single Raman peak in contrast to other TMDs. As the dimensionality is lowered, the observed peak splits in two. In contrast, our ab initio calculations predict that the degeneracy is retained even for WSe 2 monolayers. Interestingly, for minuscule biaxial strain, the degeneracy is preserved, but once the crystal symmetry is broken by a small uniaxial strain, the degeneracy is lifted. Our calculated phonon dispersion for uniaxially strained WSe 2 shows a good match to the measured Raman spectrum, which suggests that uniaxial strain exists in WSe 2 flakes, possibly induced during the sample preparation and/or as a result of the interaction between WSe 2 and the substrate. Furthermore, we find that WSe 2 undergoes an indirect-to-direct band-gap transition from bulk to monolayers, which is ubiquitous for semiconducting TMDs. These results not only allow us to understand the vibrational and electronic properties of WSe 2 , but also point to effects of the interaction between the monolayer TMDs and the substrate on the vibrational and electronic properties.

A theoretical study of a planar electronic waveguide with a uniformly curved section in the perpendicular homogeneous magnetic field B is presented within the envelope function approximation. Utilizing analytical solutions in each part of the waveguide, exact expressions are derived for the scattering and reflection matrices and for the transcendental equation defining bound-state energies. It is shown that in the magnetic field a propagation threshold in the continuously curved channel is always smaller than its counterpart for the straight arm which means that bound states in the uniform magnetic field always exist. Their energies do not depend on the direction of the field, and at high magnetic intensities they approach the lowest Landau level. For the transport in the fundamental mode an interaction of a quasibound level split off from the higher-lying threshold as a result of the bend, with its degenerate continuum counterpart, causes a dip in the transmission. In the magnetic field, contrary to the field-free case, conductance in the minimum G min , generally, ceases to be zero. It is shown that growing magnetic fields cause G min to saturate to 2e 2 / h which means that a quasibound level formed as a result of the bend is completely dissolved by the increasing B; however, this transformation is very different for the different bend angles and radii. In particular, quasibound states of the fundamental propagation mode survive stronger fields for the smaller bend angles which is explained by the larger total magnetic flux through the curved section where these levels are formed. Since a magnetic length l B = ͑ប / eB͒ 1/2 is inversely proportional to the square root of B, states for the waveguide with a smaller radius also survive stronger fields, and their asymptotic approach to the dissolution possesses nonmonotonic G min dependence on the magnetic field with minimum conductance again reaching zero for some special values of B. Vortex structure of the currents flowing in the waveguide near the resonance is strongly affected by the field. In particular, small magnetic intensities change zero-field vortices in the straight arms into the magnetic antivortices which correspond to the interacting with each other surface currents flowing along opposite walls of the channel. Increasing the magnetic field suppresses the formation of the vortices pushing currents to the outer ͑inner͒ walls in the straight ͑bent͒ section. For fields larger than the saturation magnetic intensity, the only consequence of the bend is a strong surface current near the convex wall of the bend, and the electronic flow along the junctions between straight and curved parts. FIG. 5. ͑Color online͒ Wave function ⌿͑x , y͒ ͑normalized to its maximum͒ of the bound state for 0 = 0.001 and the right angle for ͑a͒ B =0, ͑b͒ B = 10, ͑c͒ B = 20, and ͑d͒ B = 35. O. OLENDSKI AND L. MIKHAILOVSKA PHYSICAL REVIEW B 72, 235314 ͑2005͒ 235314-10

Block copolymers (BCPs) and their directed self-assembly (DSA) has emerged as a realizable complementary tool to aid optical patterning of device elements for future integrated circuit advancements. Methods to enhance BCP etch contrast for DSA application and further potential applications of inorganic nanomaterial features (e.g., semiconductor, dielectric, metal and metal oxide) are examined. Strategies to modify, infiltrate and controllably deposit inorganic materials by utilizing neat self-assembled BCP thin films open a rich design space to fabricate functional features in the nanoscale regime. An understanding and overview on innovative ways for the selective inclusion/infiltration or deposition of inorganic moieties in microphase separated BCP nanopatterns is provided. Early initial inclusion methods in the field and exciting contemporary reports to further augment etch contrast in BCPs for pattern transfer application are described. Specifically, the use of evaporation and sputtering methods, atomic layer deposition, sequential infiltration synthesis, metal-salt inclusion and aqueous metal reduction methodologies forming isolated nanofeatures are highlighted in di-BCP systems. Functionalities and newly reported uses for electronic and non-electronic technologies based on the inherent properties of incorporated inorganic nanostructures using di-BCP templates are highlighted. We outline the potential for extension of incorporation methods to triblock copolymer features for more diverse applications. Challenges and emerging areas of interest for inorganic infiltration of BCPs are also discussed.

The stability and band bowing effects of two-dimensional transition metal dichalcogenide alloys MX 2(1Àx) X 0 2x (M ¼ Mo, W, and X, X 0 ¼ S, Se, Te) are investigated by employing the cluster expansion method and the special quasi-random structure approach. It is shown that for (S, Se) alloys, there exist stable ordered alloy structures with concentration x equal to 1/3, 1/2, and 2/3, which can be explained by the small lattice mismatch between the constituents and a large additional charge exchange, while no ordered configuration exists for (Se, Te) and (S, Te) alloys at 0 K. The calculated phase diagrams indicate that complete miscibility in the alloys can be achieved at moderate temperatures. The bowing in lattice constant for the alloys is quite small, while the bowing in band gap, and more so in band edge positions, is much more significant. By decomposing the formation of alloy into multiple steps, it is found that the band bowing is the joint effect of volume deformation, chemical difference, and a low-dimensionality enhanced structure relaxation. The direct band gaps in these alloys continuously tunable from 1.8 eV to 1.0 eV, along with the moderate miscibility temperatures, make them good candidates for two-dimensional optoelectronics. V C 2013 American Institute of Physics. [http://dx.

New candidate ground states at 1∶4, 1∶2, and 1∶1 compositions are identified in the well-known Fe-B system via a combination of ab initio high-throughput and evolutionary searches. We show that the proposed oP12-FeB2 stabilizes by a break up of 2D boron layers into 1D chains while oP10-FeB4 stabilizes by a distortion of a 3D boron network. The uniqueness of these configurations gives rise to a set of remarkable properties: oP12-FeB2 is expected to be the first semiconducting metal diboride and oP10-FeB4 is shown to have the potential for phonon-mediated superconductivity with a Tc of 15–20 K.

This paper reviews progress in ultraviolet (UV) optoelectronic devices based on AlGaN films and their quantum wells (QWs), grown by plasma-assisted molecular beam epitaxy. A growth mode, leading to band-structure potential fluctuations and resulting in AlGaN multiple QWs with internal quantum efficiency as high as 68%, is discussed. Atomic ordering in these alloys, which is different from that observed in traditional III–V alloys, and its effect on device performance is also addressed. Finally, progress in UV-light-emitting diodes, UV lasers, UV detectors, electroabsorption modulators, and distributed Bragg reflectors is presented.

Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions of the effective mass Schrödinger equation. We have treated the distribution of indium atoms as random and found that the resultant fluctuations in alloy concentration can localize the carriers. By using a locally varying indium concentration function we have calculated the contribution to the potential energy of the carriers from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We have considered the effect of well width fluctuations and found that these contribute to electron localization, but not to hole localization. We also simulate low temperature photoluminescence spectra and find good agreement with experiment. arXiv:1006.1232v1 [cond-mat.mes-hall]

The exhibition of plasmon resonances in twodimensional
(2D) semiconductor compounds is desirable for
many applications. Here, by electrochemically intercalating
lithium into 2D molybdenum disulfide (MoS2) nanoflakes,
plasmon resonances in the visible and near UV wavelength
ranges are achieved. These plasmon resonances are controlled
by the high doping level of the nanoflakes after the
intercalation, producing two distinct resonance peak areas
based on the crystal arrangements. The system is also
benchmarked for biosensing using bovine serum albumin.
This work provides a foundation for developing future 2D
MoS2 based biological and optical units.

We present results of ab initio calculations for vacancies and divacancies in GaN. Particular attention is paid to nitrogen vacancies and mixed Ga-N divacancies in negatively charged states, which in n-type GaN are found to be energetically comparable with gallium vacancies. We also demonstrate that the activation energy for self-diffusion over the nitrogen sublattice is lower than over the gallium one for all Fermi-level positions, which implies the nitrogen vacancies are major defects in samples annealed at high temperatures. Possibilities for direct observations of nitrogen vacancies through positron annihilation experiments are discussed.

A high-voltage transmission line pulse transformer has been constructed based on modem cable technology. The transformer has been successfully tested for secondary voltages up to 85 kV. The high-voltage cable is equipped with a resistive layer (semicon) on the inner conductor and on the inside of the outer conductor. Semicon cables are commonly used in high-voltage transmission of electrical power.

The in-plane transport properties of a strained (100) Si layer on a relaxed Si1−xGex substrate are studied with an ensemble Monte Carlo technique. Similar velocity (-field) characteristics are found for strained Si with any valley splitting energy ΔE≥0.1 eV. These phonon-limited electron mobilities reach 4000 cm2/V s at 300 K, and 23 000 cm2/V s at 77 K. There is only a slight increase in the saturation velocity at both temperatures. However, a significant overshoot peak transient velocity is found to depend upon ΔE, and for ΔE=0.4 eV, reaches 4.1 × 10^7 cm/s at 300 K, and 5.2 × 10^7 cm/s at 77 K.

The first experimental results of the temperature dependent radiative properties of separation by implantation of oxygen (SIMOX) wafers, in the literature, have been reported in this study. These measurements have been performed in the temperature range of 17 to 800 C and wavelength range of 0.8 to 20 m using a spectral emissometer. A modeling approach based on Multi-Rad, a matrix method of representing multi-layers, has been adopted to interpret the experimental data. Operating ranges of wavelength for pyrometry have been suggested for a reliable monitoring of temperature for processing SIMOX wafers.

The dynamics of photoexcited electrons in GaAs and InP were studied using the transmission of 200-fs pulses of far-infrared radiation in the spectral range 15-100 cm-'. Kinetic traces of the infrared transmission as a function of delay between optical excitation and infrared probe show a probe-limited decrease in transmission followed by a more gradual (0.7-2 ps) drop to a steady value, consistent with the slow return of electrons from high-mass satellite valleys. Infrared transmission spectra, analyzed in the context of a Drude model, reveal density-dependent electron mobilities 34 times below equilibrium n-doped values. Electron-hole collisions likely account for the lower mobility.

Explosive progress in semiconductors physics and technology over the last century has led to replacement of almost all electro-vacuum devices with their corresponding solid-state counterparts. The only remaining exceptions were vacuum photomultiplier tubes (PMTs). In this paper, physical and technological problems are analyzed, the solution of which led to the creation of the most capable solid-state analogues of the well-known PMTs-silicon photomultipliers (SiPMs). Mass application of SiPM devices is planned in large-scale colliders, such as LHC, NICA, JUNO, and others. The status, prospects and ways of further improving the parameters of SiPMs are discussed.

The results of an ongoing collaborative project between the New Jersey Institute of Technology (NJIT) and SEMATECH on the temperature-dependent emissivity of silicon-related materials and structures are presented in this study. These results have been acquired using a spectral emissometer. This emissometer consists of a Fourier Transform Infra-Red (FTIR) spectrometer designed specifically to facilitate simultaneous measurements of surface spectral emittance and temperature by using optical techniques over the near- and mid-IR spectral range and temperatures ranging from 300 K to 2000 K. This noncontact, real-time technique has been used to measure radiative properties as a function of temperature and wavelength for a wide range of silicon-related materials and structures. The first results of the temperature and wavelength dependent emissivity and hence refractive index of silicon nitride, in the literature, is presented in this study

Spatially uniform excitations can induce Floquet topological bandstructures within insulators which have equal characteristics to those of topological insulators. Going beyond we demonstrate in this article the evolution of Floquet topological quantum states for electromagnetically driven semiconductor bulk matter. We show the direct physical impact of the mathematical precision of the Floquet-Keldysh theory when we solve the driven system of a generalized Hubbard model with our framework of dynamical mean field theory (DMFT) in the non-equilibrium. We explain the physical consequences of the topological non-equilibrium effects in our results for correlated sysems with impact on optoelectronic applications.

We report on the effect of strain on the optical and structural properties of 5-, 10-, and 20- period GaN/AlN superlattices (SLs) deposited by plasma-assisted molecular beam epitaxy. The deformation state in SLs has been studied by high resolution transmission electron microscopy (HRTEM), X-ray diffraction, and micro-Raman, Fourier transform infrared (FTIR), and photoluminescence spectroscopy. HRTEM images showed that the structural quality of the SL layers is significantly improved and the interfaces become very sharp on the atomic level with an increase of the SL periods. A combined analysis through XRD, Raman, and FTIR reflectance spectroscopy found that with increasing number of SL periods, the strain in the GaN quantum wells (QWs) increases and the AlN barrier is relaxed. Based on the dependence of the frequency shift of the E2High and E1TO Raman and IR modes on the deformation in the layers, the values of the biaxial stress coefficients as well as the phonon deformation potentials of these modes in both GaN and AlN were determined. With increasing number of SL periods, the QW emission considerably redshifted in the range lower than the GaN band gap due to the quantum confined Stark effect. The influence of strain obtained by the XRD, Raman, and FTIR spectra on the structural parameters and QW emission of GaN/AlN SLs with different numbers of periods is discussed.

Sessile drop experiments were performed on molten indium antimonide on clean quartz (fused silica) surfaces. A cell was constructed through which argon, helium, oxygen, hydrogen or a mixture of these was flowed at 600 1C. Some of the InSb was doped with 0.1% Ga. The surface tension s of oxide-free molten InSb was smaller in Ar than in He, may have increased with increasing O 2 in the gas, and was not influenced by Ga or H 2 . The contact angle y on silica was higher in the presence of Ar, was lowered by O 2 , and was not influenced by H 2 or Ga. The work of adhesion W and the surface energy s sv of the silica were higher in He than in Ar. The surface remained free of solid oxide only in flowing gas containing p0.8 ppm O 2 . This behavior is attributed to reaction of O 2 at the surface of the melt to form In 2 O gas. When solid oxide formed on Ga-doped material, it was strongly enriched in Ga, with the Ga/In ratio increasing with the concentration of O 2 in the gas.

Transport properties of ungated Si/Si1-xGex are studied by an ensemble Monte Carlo technique. The device performance is studied with a quantum hydrodynamic equation method using the Monte Carlo results. The phonon-scattering limited mobility is enhanced over bulk Si, and is found to reach 23000 cm2/Vs at 77 K and 4000 cm2/Vs at 300 K. The saturation velocity is increased slightly compared with the bulk value at both temperatures. A significant velocity overshoot, several times larger than the saturation velocity, is also found. In a typical modulation-doped field-effect-transistor, the calculated transconductance for a 0.18 μm gate device is found to be 300 mS/mm at 300 K. Velocity overshoot in the strained Si channel is observed, and is an important contribution to the transconductance. The inclusion of the quantum correction increases the total current by as much as 15%

Both the origins of the high open circuit voltages (VOC) in amorphous silicon solar cells having p layers prepared with very high hydrogen dilution and the physical structure of these optimum p layers remain poorly understood topics, with several studies offering conflicting views. This work attempts to overcome the limitations of previous studies by combining insights available from electronic measurements, real time spectroscopic ellipsometry, atomic force microscopy, and both high-resolution transmission electron microscopy (TEM) and dark field TEM of cross sections of entire solar cells. It is found that solar cells fabricated with p layers having a low volume fraction of nanocrystals embedded in a protocrystalline Si:H matrix possess lower recombination at the i/p interface than standard cells and deliver a higher VOC. The growth of the p layers follows a thickness evolution in which pure protocrystalline character is observed at the interface to the i layer. However, a low density of nanocrystallites nucleates with increasing thickness. The advantages offered by the protocrystalline character associated with the amorphous phase of the mixed-phase (amorphous+nanocrystalline) p layers prepared with excess H2 dilution account for the improved VOC of the optimum p layers. In this model, the appearance of a low volume fraction of nanocrystals near the top transparent conductor interface is proposed to be incidental to the high VOC.

A theoretical analysis of carbon nanotube based field-effect transistors fabricated by two different groups [Tans et al., Nature (London) 393, 49 (1998); Martel et al., Appl. Phys. Lett. 73, 2447 (1998)] is presented. The metal (electrode)-semiconductor (nanotube) contact influences subthreshold channel conductance versus gate voltage VG, such that the occurrence of a kink depends on the transport mechanism across this contact. Saturation in the turn-on drain current ID vs VG seen in experiments reflects the nanotube state density. Saturationless ID versus drain voltage VD indicates transport in the weak-localization regime in the absence of carrier–carrier scattering so that pinch-off cannot occur. To compensate for saturationless ID(VD) in digital applications, nanotube transistors need to be designed to maximize their transconductance.

The electron spin is a natural two level system that allows a qubit to be encoded. When localized in a gate defined quantum dot, the electron spin provides a promising platform for a future functional quantum computer. The essential ingredient of any quantum computer is entanglement-between electron spin qubits-commonly achieved via the exchange interaction. Nevertheless, there is an immense challenge as to how to scale the system up to include many qubits. Here we propose a novel architecture of a large scale quantum computer based on a realization of long-distance quantum gates between electron spins localized in quantum dots. The crucial ingredients of such a long-distance coupling are floating metallic gates that mediate electrostatic coupling over large distances. We show, both analytically and numerically, that distant electron spins in an array of quantum dots can be coupled selectively, with coupling strengths that are larger than the electron spin decay and with switching times on the order of nanoseconds.

The small silicon chip of Schottky diode (0.8 × 0.8 × 0.4 mm³) with planar arrangement of electrodes (chip PSD) as temperature sensor, which functions under the operating conditions of pressure sensor, was developed. The forward current-voltage I-V characteristic of chip PSD is determined by potential barrier between Mo and n-Si (ND = 3 × 10¹⁵ cm⁻³). Forward voltage UF = 208 ± 6 mV and temperature coefficient TC = -1.635 ± 0.015 mV/°C (with linearity kT < 0.4% for temperature range of -65 to +85 °C) at supply current IF =1 mA is achieved. The reverse I-V characteristic has high breakdown voltage UBR > 85 V and low leakage current IL < 5 μA at 25 °C and IL < 130 μA at 85 °C (UR = 20 V) because chip PSD contains the structure of two p-type guard rings along the anode perimeter. The application of PSD chip for wider temperature range from -65 to +115 °C is proved. The separate chip PSD of temperature sensor located at a distance of less than 1.5 mm from the pressure sensor chip. The PSD chip transmits input data for temperature compensation of pressure sensor errors by ASIC and for direct temperature measurement.

Since the onset of SiO2 / Si devices in the 1960's, the only basic change in the design of a MOSFET has been in the gate length. The channel thickness has fundamentally remained
unchanged, as the inversion layer in a silicon MOSFET is still about 10 nm thick. Bipolar transistor base widths have been of sub-micron dimensions all this time. It is time for a
new property to become omnipresent in concert with the high mobility strained-silicon channels and silicon-germanium alloys. This property is the inherently low parasitic series resistance of Schottky barrier contacts. Schottky contacts, beam leads, and microbridges, while originally developed in silicon, have been successfully integrated into compound semiconductors for optoelectronics. Reintroduction of these technologies
in optoelectronics based on silicon-germanium is proposed. Several new applications using platinum and rhodium compounds of silicon and germanium are presented.

One of the top efficient nonlinear optical crystals, ZnGeP 2 , is being used at present in parametric oscillators and second-harmonic and combination frequency generators for the mid-IR spectral range. Until recently, this crystal has not been thought of as a magnetic medium, and strong magnetic phenomena were assumed to not occur in it. The recent discovery of a new magnetically ordered state in ZnGeP 2 and CdGeP 2 single crystals and films doped with Mn shows that this material exhibits ferromagnetic phenomena and, if deposited on a host nonlinear single crystal, can be considered a promising magneto-optical medium. We report on nonlinear parameters of undoped and doped ZnGeP 2 and current data on magnetic phenomena in (Zn,Mn)GeP 2 and (Cd,Mn)GeP 2 ferromagnetic layers and doped ZnGeP 2 : Mn single crystals. Stabilizing a heterosystem constituted by ferromagnetic layers on a nonmagnetic nonlinear crystal extends the scope of possible designs of magneto-optical, spin-dependent, and magnetically controllable nonlinear optical devices. crystals with the best-achieved nonlinear optical parameters and the properties of Mn-doped ZnGeP 2 and CdGeP 2 crystals.

Research of pressure sensor chip utilizing novel electrical circuit with bipolar-junction transistor-based (BJT) piezosensitive differential amplifier with negative feedback loop (PDA-NFL) for 5 kPa differential range was done. The significant advantages of developed chip PDA-NFL in the comparative analysis of advanced pressure sensor analogs, which are using the Wheatstone piezoresistive bridge, are clearly shown. The experimental results prove that pressure sensor chip PDA-NFL with 4.0×4.0 mm2 chip area has sensitivity S = 11.2 ± 1.8 mV/V/kPa with nonlinearity of 2KNLback = 0.11 ± 0.09 %/FS (pressure is applied from the back side of pressure sensor chip) and 2KNLtop = 0.18 ± 0.09 %/FS (pressure is applied from the top side of pressure sensor chip). All temperature characteristics have low errors, because the precision elements balance of PDA-NFL electric circuit was used. Additionally, the burst pressure is 80 times higher than the working range.

Quantum dots (QDs) are steadily being implemented as down-conversion phosphors in market-ready display products to enhance color rendering, brightness , and energy efficiency. However, for adequate longevity, QDs must be encased in a protective barrier that separates them from ambient oxygen and humidity, and device architectures are designed to avoid significant heating of the QDs as well as direct contact between the QDs and the excitation source. In order to increase the utility of QDs in display technologies and to extend their usefulness to more demanding applications as, for example, alternative phosphors for solid-state lighting (SSL), QDs must retain their photoluminescence emission properties over extended periods of time under conditions of high temperature and high light flux. Doing so would simplify the fabrication costs for QD display technologies and enable QDs to be used as down-conversion materials in light-emitting diodes for SSL, where direct-on-chip configurations expose the emitters to temperatures approaching 100 °C and to photon fluxes from 0.1 W/mm 2 to potentially 10 W/mm 2. Here, we investigate the photobleaching processes of single QDs exposed to controlled temperature and photon flux. In particular, we investigate two types of room-temperature-stable core/thick-shell QDs, known as " giant " QDs for which shell growth is conducted using either a standard layer-by-layer technique or by a continuous injection method. We determine the mechanistic pathways responsible for thermally-assisted photodegradation, distinguishing effects of hot-carrier trapping and QD charging. The findings presented here will assist in the further development of advanced QD heterostructures for maximum device lifetime stability.

We present an atomistic study of the strain field, the one-particle electronic spectrum and the oscillator strength of the fundamental optical transition in chemically disordered InxGa1−xAs pyramidal quantum dots
QDs. Interdiffusion across the interfaces of an originally “pure” InAs dot buried in a GaAs matrix is simulated through a simple model, leading to atomic configurations where the abrupt heterointerfaces are replaced by a spatially inhomogeneous composition profile x. Structural relaxation and the strain field calculations are performed through the Keating valence force field model, while the electronic and optical properties are determined within the empirical tight-binding approach. We analyze the relative impact of two different aspects of the chemical disorder, namely:
i the effect of the strain relief inside the QD, and
ii the purely chemical effect
due to the group-III atomic species interdiffusion. We find that these effects may be quantitatively comparable, significantly affecting the electronic and optical properties of the dot. Our results are discussed in comparison with recent luminescence studies of intermixed QDs.

Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening. V C 2014 AIP Publishing LLC.

A model is proposed for the previously reported lower Schottky barrier ΦBh for hole transport in air than in vacuum at a junction between the metallic electrode and semiconducting carbon nanotube (CNT). We consider the electrostatics in a transition region between the electrode and CNT in the presence or absence of oxygen molecules (air or vacuum), where an appreciable potential drop occurs. The role of oxygen molecules is to increase this potential drop with a negative oxygen charge, leading to lower ΦBh in air. The Schottky barrier modulation is large when a CNT depletion mode is involved, while the modulation is negligible when a CNT accumulation mode is involved. The mechanism prevails in both p- and n-CNT’s, and the model consistently explains the key experimental findings.

We implement externally excited ZnO Mie resonators in a framework of a generalized Hubbard Hamiltonian to investigate the lifetimes of excitons and exciton-polaritons out of thermodynamical equilibrium. Our results are derived by a Floquet-Keldysh-Green's formalism with Dynamical Mean Field Theory (DMFT) and a second order iterative perturbation theory solver (IPT). We find that the Fano resonance which originates from coupling of the continuum of electronic density of states to the semiconductor Mie resonator yields polaritons with lifetimes between 0.6 ps and 1.45 ps. These results are compared to ZnO polariton lasers and to ZnO random lasers. We interpret the peaks of the exciton-polariton lifetimes in our results as a sign of gain narrowing which may lead to stable polariton lasing modes in the single excited ZnO Mie resonator. This form of gain may lead to polariton random lasing in an ensemble of ZnO Mie resonators in the non-equilibrium. PACS: 42.55.-f lasers;71.10.-w theories and models of many-electron systems; 42.50.Hz strong-field excitation of optical transitions in quantum systems; multi-photon processes; dynamic Stark shift; 74.40+ Fluctuations; 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices, and topological excitations;72.20.Ht high-field and nonlinear effects;71.36.+c polaritons; 71.35.-y excitons and related phenomena;42.55.Px semiconductor lasers, laser diodes;89.75.-k complex systems 0. Introduction Semiconductor micro-cavities operating in the strong coupling regime are optical resonators in which the eigenmodes are no longer purely excitonic or photonic, but a mixed light matter state is occurring. This evolution has finally led to polariton lasing [1-9]. Random lasing [10] has been claimed to be fundamentally incompatible with polaritons. From recent research developments however it turns out that it is not yet clear whether random lasers are either pure photon lasers or pure polariton lasers, or whether they even have both characteristics at the same time [11]. Thresholds like in conventional lasers may be observed [12,13]. We show in this article that for excitations of the quantum many-body system of ZnO nano-resonators by experimentally feasible threshold intensities of the optical pump found in random laser experiments we derive theoretically well confined peaks in terms of gain narrowing in the spectrum of the lifetime for the cavity polariton in the non-equilibrium. These peaks

In this study, the special quasi-random structure (SQS) approach has been
considered for structural, electronic and optical properties of rock-salt (RS) and zinc-blende
(ZB) phases of ZnO 1− x Te x (x= 0, 0.25, 0.5, 0.75 and 1) using density functional theory.
The Wu–Cohen generalized gradient approximation (GGA) has been employed for
optimizing the lattice parameters (a 0) and bulk moduli (B 0) in both phases which show
reasonable agreement with numerous theoretical and experimental results. To compute

The dielectric properties of Au/(1 % graphene
doped-Ca1.9Pr0.1Co4Ox)/n-Si structures were investigated
by the impedance spectroscopy method including capacitance–
voltage (C–V) and conductance–voltage (G/x–
V) measurements in the frequency range of 10–2 MHz at
room temperature. The experimental results show that the
real and imaginary parts of dielectric constant (e0, e00) and
electric modulus (M0 andM00), and ac electrical conductivity
(rac) are a strong functions of frequency and voltage, both.
Negative dielectric constant behavior was observed at sufficiently
high forward bias voltages at low frequencies and it
was attributed to the interfacial polarization, interface traps
and series resistance. e0 decreases with increasing frequency
at sufficiently high biases whereas e00 increases. Since
interfacial polarization and interface states, both, can follow
the ac external signal easily at low frequencies, there occurs
a contribution to the measured capacitance and conductance.
The negative values of e0 correspond to maximum value of
e00. Such contrary behavior in the e0 and e00 appears as an
abnormality when compared to the conventional behavior
metal–semiconductor structures with and without interfacial
layer. Experimental results confirmed that the dielectric
properties of these structures are quite sensitive to the frequency and applied bias voltage, both, especially at low
frequencies and high voltages because of density distribution
of interface states and interfacial polarization.

Epitaxial Si-O superlattices consist of alternating periods of crystalline Si layers and atomic layers of oxygen (O) with interesting electronic and optical properties. To understand the fundamentals of Si epitaxy on O atomic layers, we investigate the O surface species that can allow epitaxial Si chemical vapor deposition using silane. The surface reaction of ozone on H-terminated Si(100) is used for the O deposition. The oxygen content is controlled precisely at and near the atomic layer level and has a critical impact on the subsequent Si deposition. There exists only a small window of O-contents, i.e. 0.7-0.9 atomic layers, for which the epitaxial deposition of Si can be realized. At these low O-contents, the O atoms are incorporated in the Si-Si dimers or back bonds (-OSiH), with the surface Si atoms mainly in the 1+ oxidation state, as indicated by infrared spectroscopy. This surface enables epitaxial seeding of Si. For O-contents higher than one atomic layer, the additional O atoms are incorporated in the Si-Si back bonds as well as in the Si-H bonds, where hydroxyl groups (-Si-OH) are created. In this case, the Si deposition thereon becomes completely amorphous.

The calculation of the optical gaps of a series of nonmagnetic direct and indirect semiconductors and simple oxides is addressed using an all-electron perturbative method based on density-functional theory. Hybrid exchange, in both the Kohn-Sham spectrum and the perturbative response, is shown to be essential to achieve an accuracy comparable to experimental estimates for all systems studied, including those exhibiting excitonic transitions at the absorption edge. In agreement with existing evidence it is shown that a proper description of excitonic features relies crucially on the nonlocality of the response equations.

A substrate for future atomic chain electronics, where adatoms are placed at designated positions and form atomically precise device components, is studies theoretically. Since the van der Waals force turns out inappropriately weak, adatoms have to be secured with chemical bonding to the substrate atoms, but then electronic isolation between the adatom and substrate systems is not always guaranteed. A chain model shows that good isolation is expected on an s-p crossing substrate such as Si, Ge, or GaAs through surface localization, reflecting the bulk nature of the substrate. Isolation is better if adatoms are electronically similar to the substrate atoms, and can be manipulated by hydrogenation. Chain structures with group IV adatoms with two chemical bonds, or group III adatoms with one chemical bond, are semiconducting, reflecting the surface nature of the substrate. These structures are unintentionally doped due to the charge transfer across the chemical bonds. Physical properties of adatom chains have to be considered for the unified adatom and substrate systems.

An equivalent circuit model is proposed for the Schottky barrier at the junction between a metallic electrode and a semiconducting carbon nanotube (NT). We have applied the model to a gold-NT junction under the presence of neutral polarized NH3 molecules, and have shown that visible Schottky barrier modulation is possible for the gas densities as low as 3 x 10^13 cm−2, which is quite feasible experimentally.

We perform a systematic study on the growth of epitaxial Silicon–Oxygen superlattices (SLs) and investigate the impact of structural properties on the electrical performance. Si layers and O atomic layers (ALs) are deposited using SiH 4 and O 3 reactions respectively. Although the deposition of O ALs and epitaxial Si thereon, i.e. 1 st period of Si–O SL is well documented, the controlled deposition in maintaining the overall crystalline quality of SL is still a challenge. This is due to inability to limit the O layer to sub-AL content (1AL = 6.7 × 10 14 at/cm 2) at higher periods (≥2). The Si surface prior to O AL deposition is chemically modified with H-passivation and sub-AL O-content is achieved. This ensures minimum structural distortions, enabling epitaxial ordering of Si and hence the epitaxial Si–O SL up to 5-periods. No SiO x clusters are detected and O layers are stable at Si deposition temperature. Electrically, donor defects increase with Si–O periods and partially reduced with forming gas anneal. The presence of defects and increased roughness during the growth, degrade the mobility due to coulomb and surface scattering respectively. It can be circumvented by optimizing SL parameters and other process integration parameters subjected for future research.

Recently, we have found an additional spin-orbit (SO) interaction in quantum wells with two subbands [ Bernardes et al. Phys. Rev. Lett. 99 076603 (2007)]. This new SO term is nonzero even in symmetric geometries, as it arises from the intersubband coupling between confined states of distinct parities, and its strength is comparable to that of the ordinary Rashba. Starting from the 8×8 Kane model, here we present a detailed derivation of this new SO Hamiltonian and the corresponding SO coupling. In addition, within the self-consistent Hartree approximation, we calculate the strength of this new SO coupling for realistic symmetric modulation-doped wells with two subbands. We consider gated structures with either a constant areal electron density or a constant chemical potential. In the parameter range studied, both models give similar results. By considering the effects of an external applied bias, which breaks the structural inversion symmetry of the wells, we also calculate the strength of the resulting induced Rashba couplings within each subband. Interestingly, we find that for double wells the Rashba couplings for the first and second subbands interchange signs abruptly across the zero bias, while the intersubband SO coupling exhibits a resonant behavior near this symmetric configuration. For completeness we also determine the strength of the Dresselhaus couplings and find them essentially constant as function of the applied bias.

A cryogenic bolometer has been fabricated using a bundle of single-walled carbon nanotubes as absorber. A bolometric response was observed when the device was exposed to radiation at 110 GHz. The temperature response was 0.4 mV/ K, with an intrinsic electrical responsivity at low frequency up to 10 9 V / W and noise equivalent power of 3 ϫ 10 −16 W/Hz 1/2 at 4.2 K. The response is largest at input power levels of a few femtowatts and decreases inversely proportional to the input power. Low frequency noise shows a 1 / f dependence.

A degradation mechanism in cadmium telluride (CdTe/CdS) solar cells is investigated using time-dependent numerical modeling to simulate various temperature, bias, and illumination stress conditions. The physical mechanism is based on defect generation rates that are proportional to nonequilibrium charge carrier concentrations. It is found that a commonly observed degradation
mode for CdTe/CdS solar cells can be reproduced only if defects are allowed to form in a narrow region of the absorber layer close to the CdTe/CdS junction. A key aspect of this junction degradation is that both mid-gap donor and shallow acceptor-type defects must be generated simultaneously in response to photo-excitation or applied bias. The numerical approach employed here can be extended to study other mechanisms for any photovoltaic technology.