Analysis of carrier distribution function through Smith-Purcell effect in GaAs/GaAlAs heterostructures

Cellular automaton (CA)-based device simulation is one of the most powerful tool to solve Boltzmann transport equation (BTE) of carriers in semiconductor devices. In comparison to the Monte Carlo (MC) method which suffers statistical noise problems, cell representation used in the CA method realizes noise free analysis of the carrier distribution function (DF) both in real and momentum space. However, CA requires more computer resources than MC in typical cases because cell sizes used for both real and momentum space are restricted to be small enough not to cause artificial diffusion (ADF). In this paper, a new scheme for calculation of flux among cells is proposed in which carrier distribution is interpolated between neighbor cells. The suppression of ADF is confirmed through comparisons to other simulation methods in homogeneous cases, an n/sup +/-p diode case and an n/sup +/-n-n/sup +/ structure case. Consistency with MC analysis is also demonstrated by analyzes of homogeneous cases and an n/sup +/-n-n/sup +/ case and also by a theoretical study. A speed up of at least two orders of magnitude can be obtained by introducing the new flux calculation whose accuracy is ensured with much less number of cells than conventional CA methods. Consequently, this CA method is drastically improved as a practical tool for semiconductor device modeling from the point of CPU time and accuracy.

We have obtained a simple expression that determines the effective minority carrier lifetime in macroporous silicon with periodic arrangement of infinitely long macropores as a function of bulk lifetime, surface recombination velocity of minority carriers, pore radius and the distance between the centers of macropores. This expression can be applied also to macroporous silicon with randomly distributed pores by replacing the pore radius and the distance between the centers of macropores with their average values. The distribution of steady-state excess minority carriers in macroporous silicon is calculated for the analytical model proposed by us. The calculation is made for the case when both the outer surface of macroporous silicon and the bottom of pores are illuminated with light. We observed two peaks of the distribution of steady-state excess minority carriers in macroporous silicon near the surfaces illuminated with light of wavelength 0.95 ?m. At the same time, if macroporous silicon was illuminated with light with the wavelength of 1.05 ?m, we observed only one maximum in the distribution function of the excess minority carriers, in spite of the fact that the pore bottom was also illuminated with light. It is shown that the distribution of excess minority carriers in macroporous silicon with through pores is similar to the distribution in single crystal silicon. But in this case, the effective lifetime of minority charge carriers in the effective medium of macroporous silicon, which includes silicon and the surface of pores, corresponds to the bulk minority-carrier lifetime in monocrystalline silicon.

Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p0 state in Si:Bi with optical phonons. The other one is based on the suppression of acoustic-phonon-assisted relaxation from the 2p0 state in Si:P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si:P under photoionization by a CO2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions.

A new carrier distribution function is derived to describe the the thermodynamics of carriers within localized states with a broad energy distribution. With the aid of this function, several luminescence behaviors, i.e., (1) fast redshift of peak positions at low temperatures; (2) decrease of full-width-at-half-maximum (FWHM) of luminescence band at low temperatures; and (3) blueshift of peak positions at high temperatures, frequently observed in above material systems can be explained. Finally, the model is employed to fit the experimental data of cubic InGaN thin film grown on GaAs. A good agreement between the experimental data and the theoretical fitting is obtained.

Far-ultraviolet (FUV) and far-infrared (FIR) luminosity functions (LFs) of galaxies show a strong evolution from $z = 0$ to $z = 1$, but the FIR LF evolves much stronger than the FUV one. The FUV is dominantly radiated from newly formed short-lived OB stars, while the FIR is emitted by dust grains heated by the FUV radiation field. It is known that dust is always associated with star formation activity. Thus, both FUV and FIR are tightly related to the star formation in galaxies, but in a very complicated manner. In order to disentangle the relation between FUV and FIR emissions, we estimate the UV-IR bivariate LF (BLF) of galaxies with {\sl GALEX} and {\sl AKARI} All-Sky Survey datasets. Recently we invented a new mathematical method to construct the BLF with given marginals and prescribed correlation coefficient. This method makes use of a tool from mathematical statistics, so called "copula". The copula enables us to construct a bivariate distribution function from given marginal distributions with prescribed correlation and/or dependence structure. With this new formulation and FUV and FIR univariate LFs, we analyze various FUV and FIR data with {\sl GALEX}, {\sl Spitzer}, and {\sl AKARI} to estimate the UV-IR BLF. The obtained BLFs naturally explain the nonlinear complicated relation between FUV and FIR emission from star-forming galaxies. Though the faint-end of the BLF was not well constrained for high-$z$ samples, the estimated linear correlation coefficient $\rho$ was found to be very high, and is remarkably stable with redshifts (from 0.95 at $z = 0$ to 0.85 at $z = 1.0$). This implies the evolution of the UV-IR BLF is mainly due to the different evolution of the univariate LFs, and may not be controlled by the dependence structure.

The problem of improving the efficiency of contrast enhancement for complex low-contrast images in an automatic mode with an acceptable level of computational costs is considered. A new approach to image enhancement by parameter-free intensity transformation based on an estimate of the bivariate distribution of brightness is proposed. Analysis of the bivariate distribution of brightness enables to significantly improve the efficiency of image contrast enhancement. Based on this approach, a new generalized description for the procedure of intensity transformation based on the analysis of the marginal cumulative distribution function of image brightness is proposed. The relationship between the proposed generalized description of the intensity transformation and the traditional definition of histogram equalization is shown. Based on proposed description, a new technique of modified histogram equalization is proposed. The research confirms the effectiveness of the proposed technique. The proposed technique of modified histogram equalization provides an increase in the efficiency of contrast enhancement compared to the well-known traditional technique of histogram equalization.

A variational determination of the hybrid coefficients in an spz harmonic hybrid model of the angular distribution shows that the pz mode maximizes at the liquid surface. Certain thermodynamic functions of the surface may be expressed in terms of the hybridization ratio of the coefficients.

Analysis of the experimental atomic radial distribution functions for thin amorphous films of zinc phosphides obtained by explosive laser sputtering has been performed within a fragmentary model. The experiment was carried out with an EMP-100A electron diffractometer in transmitted light at accelerating voltages of 50 and 75 kV. The films obtained by sputtering of β-ZnP2 single crystals contained nanoparticles of this phase. The films based on Zn3P2 turned out to be two-phase and consisted of dispersed Zn3P2 and β-ZnP2 nanoparticles. The composition of the film obtained on the basis of α-ZnP2 corresponded neither to any one of the known phases in the Zn-P system nor to any mixture of these phases. Crystallization of films in a divergent electron beam confirmed the results of the phase analysis performed using the model atomic radial distribution functions.

This paper proposes a dynamic global backlight dimming algorithm based on the analysis of the cumulative distribution function (CDF) of the image histogram. For each intensity level, the convexity of the CDF is calculated using the distance to the uniform histogram curve. Using these values, the proposed algorithm characterizes the shape of the CDF to find the proper clipping ratio. This ratio enables to get the maximum level data beyond which the intensity levels are clipped, as the results of backlight dimming but image distortion. The experimental results show that the proposed algorithm gives a good compromise between backlight power reduction and image quality preservation, quantified by the PSNR metric.

In fluorescent materials, light from a certain band of incident wavelengths is reradiated at longer wavelengths, i.e., with a reduced per-photon energy. While fluorescent materials are common in ev...

A model accounting for particle interaction with channel walls and collisions between particles is proposed on the basis of analysis of experimental particlevelocity distribution functions.

We present the results of a global QCD analysis of helicity parton distribution functions (PDFs) that includes the latest polarized W-lepton production data from the STAR collaboration at the Relativistic Heavy-Ion Collider (RHIC). This data allows the first extraction of a nonzero helicity light-quark sea asymmetry within a simultaneous global QCD analysis of unpolarized and helicity PDFs.

The local atomic structure of PbZrO3 (PZ) as a function of temperature has been examined using the atomic pair distribution function (PDF) analysis of the pulsed neutron powder-diffraction data. The local structure was found to be deviated significantly from the crystallographic average structure, and to vary less with the composition than the crystallographic average structure. Disordered oxygen octahedral rotations have been observed in the low-temperature antiferroelectric state. With heating the M-type rotation of octahedra becomes dominant and it persists through the intermediate phase into the high-temperature paraelectric state. The Pb displacements reflect these strong deviations, and locally have a large z-component. At room temperature, deviation of Pb displacements from the antiparallel [110] pattern was found. With increasing temperature disorder in the Pb displacement increases.

In this paper, the problem of security in multiple input multiple output (MIMO) system has been analysed in the presence of an eavesdropper in cognitive radio networks. Multiple primary and secondary users communicate with the primary and secondary receiver, respectively. The secrecy capacity at primary receiver (PR) and secondary receiver (SR) have been calculated. At first, we use zero-forcing (ZF) precoding at the relay which enhances the secrecy capacity of PR and SR by nullifying the impact of interference. Secondly, we use a scheme to improve the secrecy capacity of the PR and SR using the existing interference energy of the communication medium employing selective precoding (SP) at the relay. Finally, we employ phase alignment precoding (PAP) for further increase in the secrecy capacity for PR and SR by using the destructive part of interference. Our analysis shows that among the three precoding techniques, the best performance is achieved by using the PAP at the relay in terms of secrecy capacity, complementary cumulative distribution function (CCDF) and outage probability analysis.

Free standing chemical vapour deposition (CVD) diamond films were prepared under the gas recycling mode, where the substrate temperature ranged from 820 to 1050°C. Macro- and microtextures of the films were investigated based on the orientation distribution function (ODF) and electron backscatter diffraction (EBSD) analysis. The texture consisted of 〈001〉, 〈112〉, 〈111〉, 〈221〉 and 〈110〉 fibre components. Very high twinning frequency was observed because of the reduced purity of the deposition gas. The multi-twins appearing in series as well as in paratactic form reduced the grain size and randomised the orientation distribution. It is believed that the residual strain and stress in diamond films should relate to the fibre textures in certain extent because of the anisotropic elastic characteristics of diamond crystals.