Semiconductor Glasses Research Articles

Focus on Laboratory Equipment

Focus on Laboratory Equipment

Nanoring formation by direct-write inorganic electron-beam lithography

A direct-write inorganic lithography technique is described which is capable of forming nanoscale rings of amorphous metals and semiconductors in glasses. Near-edge electron energy loss spectroscopy and electron diffraction using a subnanometer probe are used to analyze the composition and formation mechanism of these nanorings. The optical absorption cross section of one ring is calculated by multiple scattering methods. Applications in quantum electronics and the design of media with dielectric properties are suggested.

Laser modulated optical reflectance of thin semiconductor films on glass

Semiconductor films, deposited by reactive magnetron sputtering on glass substrates, have been analyzed with the help of laser modulated optical reflectance. The results are discussed with respect to the thermal and charge carrier transport properties. Charge carrier surface recombination at the front surface and at the interface between semiconductor film and glass substrate have been identified both for microcrystalline and amorphous films.

The Influence of Matrix on Quantum Size Confinement of Semiconductor Microcrystals Doped in Glass Thin Films Prepared by RF-Sputtering

Various types of semiconductor microcrystal-doped glass thin films were successfully prepared by RF-sputtering. The blue shift of the absorption edge in the visible light region, caused by the quantum confinement effect, was observed in all the thin films. The amount of the blue shift was found to depend significantly not only on the types of semiconductor dopants and the microcrystal radius but also on the type of matrix. The blue shift of semiconductor microcrystals with a small exciton Bohr radius compared with the microcrystal radius, such as that of CuCl, showed an exciton confinement effect which was theoretically predicted. On the other hand, the blue shift of microcrystals with a large Bohr radius compared with the microcrystal radius, such as that of CdSe, has been expected to follow the electron–hole independent confinement model, but it was found to deviate significantly from the theoretical curve. In order to explain this deviation, we introduced factors, such as the Coulomb interaction between electron and hole, size-dependent dielectric constants of the dopants and the dielectric constant of matrix. Consequently, it was found that the matrices have a significant influence on the electron–hole independent confinement.

Compositional Design of Glasses with Large Second- and Third-Order Optical Nonlinearity.

In order to make a compositional design for glasses with large second- and third-order optical nonlinearity, second- and third-harmonic generation of various glasses were measured. For the glasses with large nonresonant type third-order optical nonlinearity, the nonlinear susceptibility increased in the glasses with high linear refractive index, high coordination number and high ionicity. Resonant type large third-order optical nonlinearity can be seen in semiconductor and metal microcrystals-doped glasses. In this case, the role of matrix glasses was significant on the third-order nonlinearity. For glasses with large second-order nonlinearity, external treatment was indispensable, thermal poling being effective to cause second-order optical nonlinearity.

New Compositions from Photosensitive Copolymers for Information Processing and Storage

In this work we present a number of new compositions from photosensitive copolymers for information processing and storage. A number of donor-acceptor systems from carbazolyl containing polymers, in particular from carbazolyletilmethacrylates (CEM) and oktylmethacrylates (OMA) copolymers sensitized by threenytrofluorenone (TNF) derivates and additives of photochromatic substances from indolynospirobenzpyran row are investigated. The introduction in photoplastical layers 6–10% of the photochromatical additives is increased by photosensitivity of donor-acceptor systems in 5–6 times. The greatest sensitization effect has 8′-nitro-1,3,3-three methylindolynospirobenzpyran. The appreciable sensitization effect is reached at drawing of photoplastical layers on an injection films from chalcogenide glass semiconductors. Developed on the basis of photopolymer CEM:OM donor-acceptor systems have photosensitivity 10−6 J/sm2 at 80–85°C that on 2–3 order is higher than usual systems without injection. From received compositions of photopolymers were obtains photothermoplastical carriers for registration optical information. A detailed experimental study of the kinetics of photodarking and photobleaching in photochromatic polymer films is presented in this work. As a photochromatic polymer films we have obtained photochrom 1,3,3-three methyl-6(8)-nytroindolynospirobenzpyran in butilmethachrylat-styrol copolymer, which were taken in different percentage correlation. On the base of this results were elaborated the information media for holographic image registration with resolution up to 5000 mm−1. In this work we present also the results concerning the possibilities of strengthening of polymer media with the scope to improve mechanical properties of the relief image (hardness, strength, adhesive stability) and the possibilities to make copies by hot stamping method. Layers were prepared from copolymers, which contain chemically active liaisons of 4-aminostyrol or hlycedylmethacrylat. The thermoplastic layers with relief images can be cross-linked under the action of UV-light or under the action of chemical agents. As a result the polymer layers with the relief image become mechanical hard, strength, adhesive stable, without solubility in organic solvents and with stability to high temperature. The second polymer matrix on the 4-aminostyrol and hlycedylmethacrylat thermoplastic layers can be used for the multiplication of the copies on the special thermoplastic material. Carbazolylalcylmethacrylats with oktylmethacrylats copolymers have appeared rather suitable for create of new media for use in quality of photoresist. By us were received, tested and investigated as a photoresists media photopolymer layers from carbazolylalcylmethacrylats with oktylmethacrylats copolymers. On the created photoresists layers from copolymers CEM:OMA the diffraction holographic gratings diffraction efficiency 25% and resolution capability 1500 mm−1 were obtained.

Optical field-induced mass transport in As2S3 chalcogenide glasses.

We report the observation of a photorefractivelike nonlinearity responsible for the formation of giant relief modulations in amorphous semiconductor glasses. The photoinduced softening of the matrix, formation of defects with enhanced polarizability, and their drift under the optical field gradient force is believed to be the origin of the mass transport.

Absorption and Raman scattering spectroscopies from semiconductor–glass composites

Semiconductor–glass composite films were fabricated using a dual gun RF magnetron sputtering technique. The semiconductor films are made sufficiently thin to form isolated clusters of reasonably uniform size, adjustable between 1.5 and 40 nm in diameter. The glass films are continuous and form a matrix around the isolated clusters. This structure produces semiconductor clusters whose electronic band structure is dominated by quantum confinement of the electron and hole wavefunctions. This work examines the effects of fabrication and heat treatments on the electronic band structure and LO-phonon properties of Si and Ge semiconductor clusters embedded in SiO 2. Absorption measurements indicate a blue shift in energy with heat treatment as a result of quantum confinement effects. The evolution of the absorption shift as a function of both the amorphous and crystalline states is explored using Raman scattering spectroscopy.

Size analysis of nanocrystals in semiconductor doped silicate glasses with anomalous small-angle x ray and Raman scattering

Semiconductor doped glasses containing CdSxSe1−x nanocrystallites embedded in a silicate glass matrix were investigated. The dimensions of the nanocrystallites are in the range of a few nanometers and vary as a function of a secondary heat treatment. The confinement of such quantum dots for elementary excitations depends strongly on their size. In order to obtain a mean particle size and the size distribution, anomalous small angle x-ray scattering (ASAXS) and low-frequency inelastic Raman scattering measurements were performed. The sizes and the size distributions were evaluated for samples of different mean crystallite radius and composition x. The results of Raman measurements agree well with those of ASAXS, if both the acoustic mode damping across the nanocrystallite–matrix interface and the particle size distribution are taken into account in the Raman band shape analysis. The concentration of nanocrystallites in the glass matrix was determined by using the technique of contrast variation. Scattering curves were recorded at three energies below but close to the K-absorption edge of selenium (12.66 keV) and at 9.64 keV for comparison, which is significantly below the absorption edge.

Photoluminescence and photoacoustic investigations of the photodarkening effect in CdS xSe 1− x nanocrystal-doped glasses

Photoluminescence (PL) and Photoacoustic (PA) techniques were applied to study photodarkening phenomena in CdS x Se 1− x ( x=0.26) nanocrystal-doped glasses. We found that the PL intensities decreased greatly after undergoing darkening and the PA signal intensities became higher (∼3–6%). The PA signal intensities exponentially decay below the fundamental absorption edges, of which the logarithmic slope decreases after undergoing photodarkening. This implies an increase of the effective number of the surface states of the CdS x Se 1− x nanocrystals due to darkening. These results can be explained well by a model according to which nonradiative recombination centers were activated at the semiconductor nanocrystal and glass interfaces by the darkening.

Glass-like behavior in the CDW state of the quasi-one-dimensional conductor K0.3MoO3

By measuring the electric conductivity, dielectric susceptibility and thermally stimulated depolarization of the charge density wave system K 0.3 MoO 3 , we have found two relaxation processes in the temperature range between 100-10 K. The main relaxation process representing the CDW viscosity shows a critical slowing down behavior and disappears from the measured frequency window at about 28 K. The second one appears below 50 K and becomes the dominant relaxation below 30 K with a relaxation time decreasing with temperature slower than thermally activated, probably corresponding to tunneling between pinned CDW regions. The evidence for this interpretation comes from the temperature and frequency dependence of the conductivity. Together, this gives evidence for a glass-like behavior similar to chalcogenide glass semiconductors.

Pulsed breakdown of chalcogenide glass semiconductor films in a magnetic field

The application of an external magnetic field during the breakdown of chalcogenide glass semiconductor films provides a means for space-time tracing of the evolution of the current channel and for the separation of electronic and thermal effects. The rapid movement of the current channel along the sample tends to cool it, substantially abating the influence of Joule heat and making it possible to increase the power. It is shown that breakdown is driven by a leader-streamer mechanism.

What is so exciting about non-linear viscous flow in glass, molecular dynamics simulations of brittle fracture and semiconductor–glass quantum composites

Results of recent research are reported in the areas of: (1) non-linear viscous flow in glass, (2) molecular dynamics of brittle fracture and (3) optical properties of semiconductor–glass quantum composites. In all three areas, a fundamental understanding of the underlying behavior of materials has emerged from key experiments or computer simulations. These are described here: (1) The non-linear viscosity studies have established the behavior of viscosity at high strain rates in silicate glasses. Results of measurements show marked shear thinning associated with changes in the glass structure at high shear rates. A strain-rate-dependent (SRD) viscosity equation is presented which describes well the behavior of silicate glasses. (2) Molecular dynamics computer simulations of amorphous and crystalline silica have examined brittle fracture under applied uniaxial strain. Their results begin to reveal the underlying atomic processes that take part in free surface formation and fracture. For example, an examination of the atomic dynamics at the crack tip reveals that cracks form by the coalescence of pre-existing voids in the glass structure and that fracture surfaces are formed as silicon ions are shielded from the surface by oxygen ions resulting in a predominance of oxygen ions on the fracture surface. The results also suggest a mechanism for the formation of mirror, mist and hackle regions in the fractography of fractured surfaces. (3) Experimental studies of the optical properties of semiconductors formed in a glass matrix were conducted to examine the effect of size confinement on the electronic bandgap of the semiconductors. The results reveal differences in behavior between direct-gap semiconductors (CdS, CdSe and CdTe) and indirect-gap semiconductors (Si and Ge). An analysis of the data shows that the expected blue shift in bandgap energy of direct-gap semiconductors that results from reduced crystal sizes saturates at very small sizes due to the mixing of states between conduction band side valleys and the central valley. This effect does not appear to dominate indirect-gap semiconductors allowing their size-induced bandgap blue shift to cover the entire range of visible wavelengths. This effect suggests the use of quantum confined indirect-gap materials such as Si and Ge in stacks of films with different bandgaps to produce solar cells with increased theoretical efficiency.

Ultrafast photoinduced absorption dynamics of CdS 0.4Se 0.6 nanostructure semiconductors doped in glass

The ultrafast phenomena of photoinduced absorption far below the band gap of CdS 0.4Se 0.6 nanostructure semiconductors doped in glasses were investigated by using time-resolved differential transmittance spectroscopy. The carriers populated at the semiconductor–glass interfaces within less than 1 ps after photoexcitation give rise to the ultrafast photoinduced absorption. This transient photoinduced absorption decays with a lifetime of shorter than 10 ps, which strongly depends on the excitation intensity. We assign this behavior to nongeminate electron-hole recombination at the semiconductor–glass interfaces.

Raman spectra of semiconductor nanoparticles: Disorder-activated phonons

We present Raman spectra of four semiconductor doped glasses and a single crystal of ${\mathrm{CdS}}_{0.55}{\mathrm{Se}}_{0.45}$ in the range 30--800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the backscattering geometry. This includes the first-order Raman scattering from the disorder-activated zone-edge phonons and the LO phonons. TO phonon modes are not observed, as in bulk CdS, for the excitation well above the lowest gap. We show that the asymmetric line profile of the LO phonon structure can be understood as a composite of two phonon modes: the zone center and the zone edge phonons. Disorder-activated modes in the (30--${130)\ensuremath{-}\mathrm{c}\mathrm{m}}^{\mathrm{\ensuremath{-}}1}$ range and the higher-order Raman spectra are also observed and found to be consistent with this assignment.

Resonance effects in photoluminescence from deep traps in CdSxSe1−x doped glasses

We present photoluminescence studies on CdSxSe1−x semiconductor doped glasses with gap energies ranging from about 2 to 3 eV (400–600 nm). The investigations were performed by near-resonance as well as temperature-dependent resonance Raman spectroscopy. On the basis of the strongly resonant behavior of the deep trap photoluminescence with the excitonic states of the nanocrystallites, we have demonstrated that—besides the effect of photodarkening—inconsistencies in the experimental results of semiconductor doped glasses presented in literature, could be due to changes in the electronic resonance conditions when experimental parameters are changed.

Production of solid deuterium targets by ion implantation

Solid metal, semiconductor and metallic glass samples were irradiated with deuteron atomic ions between 60 and 180 keV incident energies. Accumulation rates of deuterons in different targets were recorded by the detection of protons and neutrons via the 2H(d, p) and 2H(d, n) reactions. A simple analytical expression is given to describe the kinetics of the accumulation. The dependence of the reaction rate on the deuteron energy gives information on the concentration profile in addition to the neutron flux density spectra. A varying distortion of the implanted deuteron profiles by a change in the beam energy were also observed for different targets.

Potassium source for ion-exchange glass waveguide fabrication

We propose and demonstrate the use of a new potassium-ion source for glass waveguide fabrication based on a KI -ZnCl2 mixture. Planar waveguide were made using glasses such as BK7, Pyrex, soda lime, and commercial semiconductor doped glasses. The optical quality of the waveguides prepared compare favorably with the quality obtained using other fabrication techniques and the processing time is considerably reduced.

Time-resolved photoinduced absorption spectroscopic study on trapped carriers at semiconductor-glass interfaces

Se0.6 microcrystals was investigated by using time-resolved differential transmittance spectroscopy. The electron trapping at microcrystal–glass interfaces was found to occur within less than 1 ps after photoexcitation. At low excitation energy density, the excited electrons are trapped at point defects distributed over the nanocrystal interfaces. Such electrons give rise to long-lived photoinduced absorption with a lifetime of 3.2 ns. On the other hand, at high excitation energy density, transient absorption with a fast (60 ps) and simultaneously a slow decay component (3.2 ns) was observed. This short-lived photoinduced absorption is attributed to the electrons trapped at the shallow trap states of the semiconductor–glass interfaces.

Electrical Conductivity, Thermoelectric Power, and Thermal Conductivity of Bi29Tl35Se36 Chalcogenide Glass Semiconductors in Solid and Liquid States

The properties of chalcogenide glass semiconductors of Bi29Tl35Se36 is investigated by the electrical conductivity, thermoelectric power and thermal conductivity as a function of temperature from room temperature to near 500°C. The experimental data of the electrical conductivity and thermoelectric power are analyzed in terms of a model developed from the density of states and electrical transport in solid amorphous semiconductors[1]. The activation energy calculated from electrical conductivity data is found to be 0.11 eV for the solid and 0.66 eV for the liquid. Moreover, the coefficient of the linear decrease of energy gap with temperature was found to be γ=10.37 ×10−4eV/K°. Measurements of the thermal conductivity of our sample were carried out from the room temperature to near 500° C. These measurements of thermal conductivity were carried out using the concentric cylinder method. The temperature dependence of the thermal conductivity was explained by postulating different mechanism[2] for (λ) in semiconductors. Values of room temperature electronic and bipolar thermal conductivity [λe(30) and λbp(30)] for the investigated sample were calculated, moreover these values estimated at 0° C. The thermal conductivity due to atomic motion (λa) also is calculated. Also the thermoelectric Q-factor (Z) is calculated for our sample in solid and liquid states.