Fast linear electro-optic effect in a centrosymmetric semiconductor | Communications Physics
Some of them will produce such great local fields that will destroy all material or change its physical properties. Description of local electromagnetic fields is a continuously durable through the all history of physics and was began with publication of first articles written by Maxwell Garnett which were devoted to colors in metal glasses and metallic films [ 1 ], Lorentz [ 2 ], and later in works of Brugeman [ 3 ] was developed by Edmund Stoner from University of Leeds [ 4 ] and Osborn from Naval Research Laboratory [ 5 ].
For a complicated medium such as the binary system with components A and B the dielectric function can be estimated as following [ 5 ]:. Structural properties of material may be strictly different as for surface and thin films, as for nanostructures such as clusters or nanocrystals, as for bulk material. However, it is obviously that most amounts of media in the universe is nanostructured or even in nanocrystal phase.
For example, interplanetary dust was observed charged coupled devices CCD detectors and infrared space telescope [ 6 ]. They observed a cometary coma of Hale-Bopp comet. These observations show the great fraction of silicon in all space dust. Space dust destruction and ion formation was studied by Mann and Czechovsky [ 8 ], which results from model calculations in silicate grains, carbon and ice grains. Grain destruction in a supernova remnant shock wave was investigated by astronomers of Harvard University [ 9 ].
The case of impact of nanoscopic dust grain with solar wind of spacecraft already was estimated by using the dimensionless parameter equals to ratio between Debye length and radius of dust cloud spherical shell with radius R [ 10 ]. From the other physical scientific trends we have an observations of local field by a nonlinear spectroscopic experiments with nonmaterial and nanocomposites, particularly, semiconductors. By using semiconductor materials have been made numerous types of devices, such as electronic devices and photon detectors, integrated circuits and thin film transistors, optoelectronic devices and others.
Every time when the device is developed the problem of reproducibility of its work regimes and durability of their realization is appeared. The solution of this problem is very important for device manufacturing, and it depends on properties of used active semiconductor materials.
The electrical properties often are not so transparent due to slightly nonlinear behavior of their characteristics. Figure 1 shows the current-voltage and resistance-voltage characteristics for two silicon films prepared by plasma-enhanced chemical vapor deposition technique with gas mixture of silane diluted by hydrogen and silicon tetra fluoride gas: amorphous and nanocrystallized [ 11 ]. It is seen, than their current-voltage characteristics are similar in this voltage range, but resistance-voltage characteristics are strictly different.
Such difference can be explained by the disorder of amorphous phase and generating of numerous point defects by applying external electrical field. Hydrogenated amorphous silicon was widely used in last decades in electronics. In recent years the nanocrystalline silicon are studying for many technological applications. The structural transformation from crystal to disordered materials, however, is investigated very poor, mainly resulted in Staebler-Wronski photo-stimulated effect.
However, the electric field applied to the nanostructured silicon thin film gives the new possibility to change structural order.
Such kind of structural transformation is caused because of there are numerous defects inside the silicon film. The current-voltage and ohm-voltage characteristics for two silicon films: amorphous and nanocrystallized. The anomalous characteristic of resistance-voltage can be explained by random distributed the point defects inside the amorphous film along with the hydrogen atoms, and existing the dipoles Si-O which turn to compensate the external electric field.
But, for the nanocrystalline silicon film, the point defects are incorporated into silicon nanostructured net and cannot move freely, because there is a stabile electric characteristic for nanocrystalline silicon film, and anomalous for amorphous. The other new area of scientific interests is crystal-amorphous phase transformations by applying electric fields and role of local fields in phase transition from order to disorder. Because, it is important to investigate the point defects which can be responsible for local electrical fields generation in polarized media, such as dielectric silicon oxide media or semiconductor thin film of silicon.
The main role plays here the silicon-oxide bonding in side thin film of silicon. Si-O dipoles play a dramatic role in crystal phase destruction by applying electric fields. The induced dipole moment by applied electric field can be written in the following form [ 12 ]:. The macroscopic description and molecular nanoscopic model are poor for investigating the mechanism of crystal semiconductor structures destruction by applied electric fields because the their dielectric functions is not so transparent for these complicated media, for example SiO x , from one side, and their ratio between covalent and ion fractions of inter atomic bond are not so homogeneous, from the other side.
The present work is devoted to the nature of local field appearance in silicon nanoscopic material and role point defects in phase transformation of material. Raman effect is result from the interaction of an electromagnetic field and optical phonon mode.unmardeposibilidades.es/modules/india/1775.php
Fast linear electro-optic effect in a centrosymmetric semiconductor
Raman susceptibility. The microcrystal wave function is a superposition of Eigen functions with k vectors centered at k 0. If we are using the weighting function as Gaussian we will have. The first-order Raman spectrum. For the silicon nanocrystalline and microcrystalline films the phonons can be generated in crystals by laser field or annealing.
The wave of deformations can be generated by picoseconds laser pulse [ 16 ]. The acousto-electric effect was observed in n-type germanium [ 17 ].
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Working pressure was 0. Figure 5 shows the changes in Raman scattering spectral data by applying the external electric field. It is seen, that there is phase destruction by the relatively high voltage. It is assumed that the nanocrystals which have grain boundary with oxygen atoms incorporated into silicon were destroyed in their crystal structure by Si-O dipoles reorientations caused by applied field. The initial crystal orientation was The incorporated oxygen atoms are adsorbed in determined places.
Their position results the appearance of numerous dangling bonds which are multiplied by the electric field and create the deep cracks in crystals. The crystal order is damaged along the axis that is perpendicular to The polarization of elliptic silicon grains evaluated by fixed NDB and stark energy shifts for levels in electronic structure by external electromagnetic field. It is necessary to note that the fractal structure of several kinds of nanocrystals may cause the dramatically changes four orders of magnitude in intensity of Raman scattering due to existing of plasmon resonance into the gaps between the fractals [ 19 ].
The Raman intensity by these conditions can be expressed as. The two atoms of hydrogen in the SiH 2 unit show an average proton separation of 2. Because, for the hydrogenated silicon nanocrystalline films under influence of applying the external electric field the hydrogen diffusion increases and polysilane chains are created, surely.
I suppose that all the oxygen is concentrated around crystals in their grains boundaries. By applying external voltage it is clear that all Si-O dipoles move to compensate external field and destroy the crystal structure. Because, by applied electric field I observed the crystal phase destruction and SiOx creation by using the Raman scattering data which correspond to the results reported in work [ 21 ]. The energy shift due to the stress appearance for crystal orientation is less than 0.
This matrix can be transformed into next triangular form:.
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The probability of changing the polarization state from one to another can be described by using Golden rule of Fermi. Matrix element for such changing of polarization state from i to state j, according to theoretical work of V. Lakhno [ 23 ], can be written as. The second-harmonic generation is forbidden for center symmetric crystal such as bulk silicon because the sum dipole moment is zero, but is possible due to the surface breaking symmetry and quadruple terms contributions.
The opposite situation is for nanostructured oxidized silicon film, the surface area for a great amount of nanocrystals is significant, the breaking symmetry is permanent and lateral isotropic. Figures 5 and 6 illustrate the SHG spectra of radiation reflected from silicon films. The bandwidth of radiation is 0. The SHG response was detected by a photomultiplier tube and gated electronics with an average of pulses. The diameter of irradiated spot was 0. The second-harmonic intensity can be written as.
Resonance spectra consist of two sharp peaks. The peak at 1. The contribution of point defects as deviations of local fields and external applied electric field for a phonon generation in silicon nanocrystalline can be described by using the perturbation theory. We assume that there is no strict disorder media, but some small disorder is determined. For j components of free energy along the axis 1 and 2 on 2D plate it is surely can be presented other form of such formula:. For analysis of deformation by applying the external electrical field it is clear to use ratio between free energy components for different bonding and directions:.
Accordingly, the ratio between the polarization charges for two dipoles inside the electric field is given by. Skip to main content Skip to table of contents. Advertisement Hide. Authors view affiliations Karl W.
Survey of Semiconductor Physics
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