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Excess-carrier recombination mechanisms in undoped BaSi2 epitaxial films grown by molecular beam epitaxy on n-type silicon substrates have been studied by the microwave-detected photoconductivity decay measurement. The measured excess-carrier decay is multiexponential, and we divided it into three parts in terms of the decay rate. Measurement with various excitation laser intensities indicates that initial rapid decay is due to Auger recombination, while the second decay mode with approximately constant decay to Shockley-Read-Hall recombination. Slow decay of the third decay mode is attributed to the carrier trapping effect. To analyze Shockley-Read-Hall recombination, the formulae are developed to calculate the effective lifetime (time constant of decay) from average carrier concentration. The measurement on the films with the thickness of 50-600 nm shows that the decay due to Shockley-Read-Hall recombination is the slower in the thicker films, which is consistent with the formulae. By fitting the calculated effective lifetime to experimental ones, the recombination probability is extracted. The recombination probability is found to be positively correlated with the full width at half-maximum of the X-ray rocking curves, suggesting that dislocations are acting as recombination centers. [ABSTRACT FROM AUTHOR]

Carrier confinement and injection characteristics of polar and nonpolar III-nitride quantum well (QW) light-emitting diode or laser diode structures are compared. We demonstrate that strongly inhomogeneous QW injection in multiple-QW (MQW) active region is one of the possible reasons holding back the advance of nonpolar laser structures. In polar structures, strong interface polarization charges induce the nonuniform carrier distribution among the active QWs so that the extreme p-side QW always dominates the optical emission. On the contrary, in nonpolar MQW structures, the inhomogeneity of QW populations is supported mainly by QW residual charges and the prevailing QW is the one closest to the n-side of the diode. For both polar and nonpolar structures, the QW injection inhomogeneity is strongly affected by the QW carrier confinement and becomes more pronounced in longer wavelength emitters with deeper active QWs. We show that in nonpolar structures indium incorporation into optical waveguide layers improves the uniformity of QW injection. On the contrary, QW injection in polar structures remains inhomogeneous even at high-indium waveguide layer compositions. We show, however, that polarization-matched design of the electron-blocking layer can noticeably improve the injection uniformity in polar MQW structure and enhance the structure internal quantum efficiency. [ABSTRACT FROM AUTHOR]

The effects of ultraviolet (UV) irradiation on the relaxation processes in Ba0.3Sr0.7TiO3 thin film capacitors were experimentally investigated in a range of wavelengths λ=(310–400) nm. It was observed that irradiation with a specific wavelength reduces the time of slow capacitance relaxation up to three orders of magnitude in comparison with relaxation time in the “dark” regime. It was also observed that at a certain wavelength of UV irradiation there was a maximum in the leakage current of the capacitors. This wavelength corresponded exactly with a minimum in the relaxation time of the capacitance. It was shown that the decrease in the ferroelectric film thickness resulted in a shift in τ(λ)minima and I(λ)maxima towards the shorter wavelengths. Phenomena observed are analyzed using Bouguer’s law. [ABSTRACT FROM AUTHOR]

The microscopic states and performance of organic solar cell are investigated theoretically to explore the effect of the carrier mobility. With Ohmic contacts between the semiconductor and the metal electrodes there are two origins of carriers in the semiconductor: the photocarriers generated by photon absorption and the dark carriers diffused from the electrodes. The power efficiency of the solar cell is limited by the recombination of a carrier with either the photocarrier or a dark carrier. Near the short-circuit condition the photocarrier recombination in the semiconductor bulk decreases as the mobility increases. Near the open-circuit condition the dark carrier recombination increases with the mobility. These two opposite effects balance with one another, resulting in an optimal mobility about 10-2 cm2/V s which gives the highest power conversion efficiency. The balance of the electron and hole mobilities are not necessary to maintain the optimal efficiency also because of the balance of the photocarrier and dark carrier recombination. The efficiency remains about the same as one carrier mobility is fixed at 10-2 cm2/V s while the other one varies from 10-1 to 10-3 cm2/V s. For solar cell with a Schottky barrier between the semiconductor and the metal electrode there is no dark carrier recombination. The efficiency therefore always increases with the mobility. [ABSTRACT FROM AUTHOR]

High quality electrical resistivity ρ(T) versus temperature data of as-prepared and O2-annealed Cu0.5Tl0.5Ba2Ca2Cu3-ySnyO10-δ (y=0, 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5) superconductors has been studied for fluctuation-induced phenomena setting in at temperatures well above the critical temperature [Tc(R=0)]. The analysis of the data is done by using Aslamazov–Larkin (AL) and Lawrence–Doniach models for the excess conductivity. We have estimated several physical parameters, including coherence length, interplane coupling strength, exponents, and dimensionality of the fluctuations. The as-prepared and oxygen postannealed samples have shown a cross-over temperature associated with two distinct exponents and the excess conductivity data fits well with the two-dimensional and three-dimensional AL equations. The coherence length along the c-axis [ξc(0)] and the interlayer coupling strength (J) are found to decrease with increased Sn doping. These values are increased after annealing the samples in oxygen atmosphere, which is most likely associated with the approach of carrier concentration in the conducting CuO2/SnO2 planes to the optimum value. The Tc(R=0) and the peak temperature (TP) as determined from the dρ/dT versus temperature plots are also found to decrease with increased Sn substitution, however, these temperatures are improved to higher values after annealing the samples in oxygen atmosphere. The decreased values of Tc(R=0) and TP with increased Sn substitution in the as-prepared samples are most likely arising from the suppression of carrier’s density promoted by the increased volume of unit cell and the localization of the carriers at the Sn4+ sites. [ABSTRACT FROM AUTHOR]

Carrier relaxation dynamics in tin nitride (SnxNy) nanowires have been investigated using femtosecond transient absorption spectroscopy. The nanowires were grown directly on quartz using chemical vapor deposition and had diameters ≤200 nm and lengths up to 2 μm. Steady state optical transmission measurements suggest that the band gap is ∼2.9 eV while time resolved measurements reveal that free carrier absorption dominates the carrier dynamics and overcomes state filling within 0.5 ps of the incoming excitation pulse even when probing above the band edge. This is a unique and markedly different behavior compared to what we have observed in other semiconductor nanowires and it is attributed to fast scattering of the photogenerated carriers out of the excitation energy region and possible rise in the lattice temperature due to energy relaxation. Carrier relaxation occurs through two channels with a fast time constants of ≈200 ps and a slow time constant ranging between 5 and 8 ns while intensity measurements reveal negligible contribution from nonlinear effects such as Auger recombination. [ABSTRACT FROM AUTHOR]

Ultrafast carrier dynamics in In2O3 nanowires with an average diameter of ≈100±20 nm grown by the vapor-liquid-solid method have been investigated in detail using differential absorption spectroscopy with femtosecond resolution. Measurements revealed that state filling is important for states above the band gap and states just below the band edge, thus demonstrating the critical role that shallow traps play in the relaxation of the photogenerated carriers. Furthermore, time-resolved intensity measurements revealed the importance of Auger recombination in the relaxation of carriers in the In2O3 nanowires and provided the maximum fluence (∼3 μJ/cm2) where this recombination mechanism may be considered negligible. Transient measurements in this low-fluence regime for carriers above the band gap revealed single exponential recovery (∼1.5 ns) associated with recombination of the photogenerated carriers. Similar behavior has been observed for the photogenerated carriers distributed within the shallow traps just below the band edge. Furthermore, measurements at longer probing wavelengths provided an estimate of the nonradiative relaxation of carriers (∼300 ps), which are distributed among the midgap states. Finally, long-lived oscillations in the transient reflection were detected, which corresponds to the presence of longitudinal acoustic phonons in the In2O3 nanowires. [ABSTRACT FROM AUTHOR]

A valuable nondestructive measurement and analysis method for determining individual excess carrier lifetimes in multilayer systems is presented. This is particularly interesting for the characterization of crystalline silicon thin-film samples consisting of an electrically active epitaxial layer on top of a highly doped crystalline substrate. The analysis principle is based on a comparison between a measured photoluminescence intensity ratio and associated simulated radiative recombination ratios for samples with different epitaxial layer thicknesses. It benefits from the fact that for low excess carrier lifetimes within the epitaxial layer the carrier concentration in the said layer is limited by bulk recombination, while for high carrier lifetimes surface and interface recombination is dominating. In order to verify this measurement and analysis principle, results of a set of crystalline silicon thin-film samples with varying epitaxial layer thickness on a highly doped Czochralski substrate are presented. [ABSTRACT FROM AUTHOR]

An approach to evaluate the microwave-detected photoconductance decay (MWPCD) is developed, which allows to extract the minority carrier lifetime as a function of the excess carrier density from a single MWPCD measurement. The method is shown to be applicable to thin (w≤200 μm) silicon wafers with low minority carrier recombination at the surfaces and bulk lifetimes in the range of about 1–100 μs. Comparison of the MWPCD results with minority carrier lifetime measurements using the quasi-steady-state photoconductance method reveals very good agreement between both types of measurement. Only when the photoconductance exceeds 30% of the dark conductivity, is a deviation observed, because then the MWPCD signal is no longer directly proportional to the excess carrier density. Minority carrier trapping is found to affect the MWPCD signal only in the tail of the measured photoconductance decay. The evaluation method is used to map the interstitial iron content with high spatial resolution, as well as to determine the minority carrier trap density. An excellent agreement between numerical simulation and measured MWPCD signal is found revealing the assumptions made for the evaluation approach to be valid. This evaluation of the MWPCD measurement is well suited to characterize silicon of low purity and low crystalline quality, which is often employed to solar cells with high spatial resolution. [ABSTRACT FROM AUTHOR]

Coupled donor states induced by Sn doping into InP and their behaviors were studied by employing photoluminescence (PL) measurements and first-principles calculations. InP: Sn crystals were grown in the [100] orientation by a modified liquid-encapsulated vertical Bridgman technique. The PL data show a donor-acceptor recombination line and its phonon replica at 898 nm and 926 nm, respectively, and another recombination line around 800 nm, which uniquely appears at the top in high Sn concentration. The first-principles calculations for the InP:Sn system support these results by observing two separate donor levels below (DSn1) and above (DSn2) the bottom of the conduction band, which are responsible for the recombination lines. They deviate from the bottom of the conduction band with the increase of Sn concentration. A peak at 879 nm from the band-to-band transition could only be visible at room temperature. The PL mapping of this line shows the increase of Sn concentrations with the crystal growth, which helps to reduce the dislocation density and increase the lifetime of excess carriers. [ABSTRACT FROM AUTHOR]

Thermally stimulated current (TSC) controlled by thermal release of excess charge carriers (holes) from intrinsic traps in a conjugated polymer poly(9,9-bis(2-ethylhexyl) fluorene-2,7-diyl) has been studied at different readout voltages (VRO) applied during the heating run. We found that the TSC peak measured at low applied electric field is located at somewhat higher temperature then the thermally stimulated luminescence (TSL) detected in this material; however, the TSC peak shifts towards the lower temperature with increasing VRO and at high electric fields approaches the temperature spectra of TSL. We found that the above shift of the TSC peak is not accompanied with a substantial increase of TSC intensity usually observed in the TSC of organic solids, and is considered as an indication that the recombination of liberated charge carriers plays no role. Whereas the observed behavior of the TSC peak is due to the thermally stimulated dispersive transport of holes in the polymer. We formulated a model of dispersive TSC, which considers the partial filling of deep traps. Results of the calculations agree well qualitatively with the experiment. The possible implication of the dispersive character of TSC for evaluation of the energetic distribution and spatial concentration of traps from the TSC data is analysed. [ABSTRACT FROM AUTHOR]

Evaluates the consequences of interactions between charge carriers on the transport dynamics of currents in normally insulating one-dimensional systems where excess charges have been injected electrically, chemically or optically. Calculation of time-dependent currents and space charge distribution using a many body Monte Carlo method.

Studies the excess carriers lifetime in indium phosphide (InP) single crystals. Importance of the lifetime of excess carriers in semiconductors; Details on the experiment; Factors influencing photoluminescence decay.

Abstract We investigated an optical carrier injection mechanism in an organic semiconductor rubrene crystal. We simultaneously measured exciton photoluminescence (PL) and photocurrent under an electric field higher than 1 kV/cm at room temperature. An anti-correlation between the exciton PL intensity and photocurrent was observed. This directly indicates that carriers are generated through an exciton dissociation induced by the electric field. The estimated exciton dissociation efficiency is on the order of 10−2 for an excitation wavelength of 442 nm under an electric field of 12 kV/cm at room temperature. In addition, we revealed that both carriers and excitons are trapped at oxidation sites at the surface area of the crystal and more efficiently emit a modified luminescence. [ABSTRACT FROM AUTHOR]

Determines the anisotropy of excess charge carriers mobility in pure and mixed crystals of polydiacetylene derivatives. Use of pulse-radiolysis time-resolved microwave conductivity technique; Orientation of polymer backbone with respect to electric field direction; Absolute value of charge carrier mobility; Influence of grain boundaries on charge carrier mobility.

Examines the effects of photon recycling in a two-dimensional model accounting for the geometry of the device and the spectral content of the recombined excess carriers. Inclusion of a three-dimensional ray tracing algorithm; Angular dependence of transmissivity between layers in a heterostructure device.

Presents a study which investigated using electroluminescence as a monitor the behavior of charge carriers injected from electrodes and excitons generated by the recombination of charge carriers in multilayer organic light-emitting diodes. Background on the concerned materials; Description of the experimental setup; Results.

Deals with a study which investigated excess carrier distribution and saturation current generated by a graded p-n junction. Discussion on excess carrier distribution; Information on how the contribution of the graded region to the saturation current can be obtained.

Discusses a study which mapped the three-dimensional excess carrier distribution in semiconductor imaging arrays using a three-dimensional simulation. Mathematical equation for three-dimensional excess carrier distribution; Assumptions on excess carrier distribution; Effects of various absorption coefficients.

Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment. For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps. [ABSTRACT FROM AUTHOR]

The influence of the generation and recombination of free charge carriers in the p-i-n structure in strong electric fields on the stationary volt-ampere characteristics is considered. The issues of the stability of stationary solutions are investigated. It is shown that a form of the stationary volt-ampere characteristics and their stability depend on ratios between free electrons and holes in the current injected into the i-layer and in the current outflowing from the layer. When the structure is forward biased, the oscillations may occur. [ABSTRACT FROM AUTHOR]

Spectral photoluminescence emitted from the front compared to the rear side of a semiconductor layer like a photovoltaic absorber is shown to exhibit significant differences in the high-energy regime. This arises from the excess-carrier depth profile and the absorption of photoluminescence photons during their way through the semiconductor layer depending on photon energy, distance to the absorber exit, and absorption coefficient.We get access to surface-recombination velocities, the minority-carrier diffusion length, the excess-carrier depth profile and the optical band gap by fitting photoluminescence spectra via numerical modeling. The numerical modeling is based on an one-dimensional three-layer system that includes multiple reflection. This procedure is exemplarily demonstrated for a thin-film system based on Cu(In,Ga)Se2. [ABSTRACT FROM AUTHOR]

Abstract: Aluminum oxide provides an excellent surface passivation on p- and n-type crystalline silicon. On n-type silicon, however, the effective excess carrier lifetime τ eff is often found to be injection dependent. Our experimental results show that, in our case, this effect depends mainly on the size of the lifetime samples. The fixed negative charges present at the Al2O3/c-Si interface induce an inversion layer at the surface, which results in a p–n-junction close to the surface of the sample and the inversion layer couples the sensing area with the poorly passivated or damaged edge of the sample. For smaller samples stronger injection-dependent lifetimes are measured, whereas large samples show a smaller injection dependence. In addition, photoconductance-calibrated photoluminescence lifetime images show that for low injection levels the lifetime decreases towards the sample edge. Device simulations for different sample sizes including the edge recombination are in agreement with the measured injection-dependent lifetimes. Therefore, it is necessary to use sufficiently large samples or decouple the sensing area form the edge when evaluating the injection dependence of the lifetime. For the samples used in this contribution, the injection dependence of the lifetime did not even fully vanish for an edge length of 12.5cm. [Copyright &y& Elsevier]

SUMMARY A physically based power PiN diode model is presented. Eigen value internal approximation method is used to solve the ambipolar diffusion equation. This model is implemented in SIMPLORER circuit simulator using VHDL-AMS language. The proposed model can be used in both circuit simulators and the optimization of a given power PiN diode. Good agreement is obtained by comparing the results of the suggested model with experimental data. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A geminate reaction between A and B reactants affected by the bulk reaction between B and scavengers C is discussed. The exact solution of the problem obtained recently for randomly walking B reactant (excess electron) is compared with the superposition approximation commonly used to interpret experimental data. Distinctions related to the important role of time correlations between geminate and bulk reactions are analyzed. The largest deviations exponentially growing in time are observed for geminate reaction rate in the presence of scavengers. It is shown that superposition approximation can decrease essentially the ultimate probability of geminate recombination. The difference is great enough to lead to qualitatively incorrect description of the experiment even at small concentration of scavengers. This, in turn, may give rise to considerable errors in the determination of geminate pair parameters or, alternatively, to the wrong information about bulk kinetics of electron scavenging. [ABSTRACT FROM AUTHOR]

The combination of emitter control with local lifetime tailoring by ion irradiation is experimentally analyzed in fast-recovery high power diodes. For this purpose, the carrier lifetime and excess carrier concentration profiles are measured and modeled within the low doped region of unirradiated and helium irradiated diodes under low current densities (<20 A/cm²). The interest in working under these current conditions responds to the fact that the only recombination mechanism that modulates the steady-state carrier concentration is that of the multiphonon-assisted case (Shockley-Read-Hall model). This enables us to extract parameters for their modeling under arbitrary working conditions and to detect the influence of ion irradiation on the excess carrier distribution. For a better comprehension of the results, the excess carrier profile in the unirradiated diode is physically analyzed in detail by an analytical model. Afterward, physical simulations are also carried out, employing the experimental lifetime profiles as input parameters. As a result, a very good agreement between simulation predictions and experiments is observed, which is used to explain, by the support of analytical expressions, how the ion-irradiation process can improve the diode operation at low current densities during the late phase of the reverse recovery. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an iterative method for obtaining footprint, pressure distribution, local deformation and sub-surface stress field for the contact between a rigid cylindrical indenter and an elastic flat substrate. The methodology is applicable for semi-infinite, as well as for thin or thick bonded elastic layered solids with high or low elastic moduli. All findings are in accord with the observed behaviour of hard wear resistant and soft solid lubricating coatings. It is shown that the decomposed contact pressure distribution into a series of harmonic waves induces sub-surface stress fields that decay into the depth of the solid according to their wavelengths. Consequently, conditions vis-à-vis fatigue spalling and adhesion performance may be predicted for given thickness of layered bonded elastic solids. [Copyright &y& Elsevier]

The effect of louver baffles on gas back-mixing was investigated in a large-scale two-dimensional fluidized bed of fluid catalytic cracking (FCC) particles with helium as tracer gas. The axial gas dispersion coefficient of the baffle-free fluidized bed first increased with increasing superficial gas velocity and then decreased after reaching a maximum near the onset of the turbulent flow regime. “Gulf streaming” of emulsion flow in the baffle-free bed determined the lateral profiles of tracer gas concentration. Solids back-mixing flux was greatly reduced by the addition of a layer of louver baffles, while solids mixing above the baffle layer was enhanced. The modified baffled fluidized bed with multilayer louver baffles not only provided a high efficiency of gas−solids contacting but also greatly suppressed the back-mixing of both gas and solids. [ABSTRACT FROM AUTHOR]

Abstract: We developed a perturbation method to predict the behaviour of ionization chambers functioning in current mode when the space charges are neglected. This method allowed us to go for the first time beyond the Thomson problem by taking into account, in the output current calculation, the spatial variations of the primary charge density induced by the incident ionizing particles. The results obtained are presented under the form of series for which we studied the convergence radius and quality in a simple case. Additionally, we solved the Thomson problem when the space charges are neglected and established for the first time the explicit relationship linking the input voltage to the output current. Finally, we calculated the voltage that delimits the transition between the recombination regime and the saturation plateau. [Copyright &y& Elsevier]

Abstract: The present paper deals with a non-conventional scale transition for modelling the behaviour of highly-filled particulate composites, starting from a methodology initially proposed by Christoffersen [Christoffersen J. Bonded granulates. J Mech Phys Solids 1983;31:55–83] and recently extended by Nadot et al. [Nadot C, Dragon A, Trumel H, Fanget A. Damage modelling framework for viscoelastic particulate composites via a scale transition approach. J Theor Appl Mech 2006;44(3):553–83] in presence of damage. The model thus obtained is here completed with several ingredients allowing to describe damage evolution and in particular a defect nucleation criterion as well as a closure criterion. These criteria are formulated in terms of displacement, and so as to ensure continuity in terms of macroscopic stress. They are finally introduced in an iterative numerical solving procedure which allows to follow damage evolution as a discrete sequence of interfacial debonding including also eventual closure of defects. [Copyright &y& Elsevier]

Abstract: The object of considerations is a thin linear-elastic cylindrical shell with arbitrary cross-section having a periodic structure in both directions tangent to the shell midsurface. The aim of this paper is to propose a new averaged non-asymptotic model of dynamical stability problems for such shells. As a tool of modeling we shall apply the tolerance averaging technique, given for periodic structures in Woźniak and Wierzbicki [Averaging techniques in thermomechanics of composite solids, Wydawnictwo Politechniki Częstochowskiej, 2000]. In contrast with models obtained by means of asymptotic homogenization methods, the proposed one makes it possible to describe the effect of the period lengths on the global shell stability, called a length-scale effect. [Copyright &y& Elsevier]

Abstract: The functioning of the solar cells relies on the photo-generation of carriers in p–n junctions and their subsequent recombination in the quasi-neutral regions. A number of basic issues concerning the physics of the operation of solar cells still remain obscure. This paper reports on some unsolved basic problems, namely: a model of the recombination processes that does not contradict Maxwell''s equations; the role played by space charges in the transport phenomena, and the formation of quasi-neutral regions under the presence of non-equilibrium photo-generated carriers. In this work, a new formulation of the theory that explains the underlying physical phenomena involved in the generation of a photo-e.m.f. is presented. [Copyright &y& Elsevier]

Dependences of the spectral peak position of edge photoluminescence, its half-width, resistivity, charge carrier mobility in crystals of semi-insulating undoped GaAs on the carbon concentration N[sub c] at 77 K (3.0 x 10[sup 15] cm[sup -3] ≤ N[sub C] ≤ 4.3 x 10[sup 16] cm[sup -3]) were studied. The dependences observed are explained by the interaction of charge carriers with ionized impurity atoms and with structural defects. [ABSTRACT FROM AUTHOR]

The effect of bulk (τ) and radiative (τ[sub r]) charge-carrier lifetimes on the degree of spatial separation of the regions of the carriers' generation and radiative recombination in graded-gap semiconductors with the drift transport mechanism in the built-in quasi-electric field of the crystal was investigated experimentally and theoretically. It was found that the degree of spatial separation increases with increasing τ and/or τ[sub r]. The effect of spatial separation of the regions of radiative recombination, which correspond to transport mechanisms with various τ[sub r], was observed. The data obtained are related to the coordinate dependence of recombination probability for graded-gap semiconductors. [ABSTRACT FROM AUTHOR]

Examines the dynamics of injected carriers and the conditions for intersubband gain and inversion in semiconductor indium gallium arsenine-gallium arsenide self-organized quantum dots using direct femtosecond pump-probe spectroscopy. Electron relaxation time between excited and ground states; Analysis of carrier relaxation and phonon bottleneck.

A nondestructive method for measuring the three-dimensional distribution of the charge-carrier lifetime and diffusion length in silicon ingots with a length of up to 1 m and a diameter as large as 0.3 m is presented. Physically, this method is based on infrared crossed-beam probing of an ingot with polished surface areas. One of the beams is repetitively pulsed, has a wavelength of 1.15-1.28 µm, and generates excess charge carriers in a rodlike zone along the beam trajectory in the ingot. Other beams are continuous and have longer wavelengths; these beams detect the temporal and spatial kinetics of excess charge carriers in a small portion of the rodlike zone and in the vicinity of it (the free-carrier absorption is measured). By virtue of the fact that the investigated zone is at a distance from the ingot surface, there is no need to consider the surface recombination. The capabilities of the method are demonstrated for an ingot with known spatial nonuniformity of the charge-carrier lifetime. Spatial resolution amounting to several millimeters was attained. [ABSTRACT FROM AUTHOR]

Describes an experimental setup for investigating the electrical transport properties in semiconductors. Applications of the Haynes-Shockley experiment; Utilization of electrical or optical injection of the excess carriers; Mobility and diffusion coefficients; Measurement of recombination lifetime from the collected pulses area.

A theory of size-quantization of charge carriers in a small semiconductor crystal under conditions where the polarization interaction plays a large role is constructed. The charge-carrier spectrum in a small microcrystal and its dependence on the radius of the microcrystal, the charge-carrier effective mass, and the relative permittivity are investigated. It is shown that the appearance of local states is of a threshold nature depending on the size of the microcrystal. [ABSTRACT FROM AUTHOR]

Examines microscopic processes that do not possess a characteristic time scale, particularly transport and relaxation in disordered solids. Discussion of dispersive transport, time-of-flight measurements and random-walk theory; Experiments and mechanisms of disorder in the form of a distribution of trap states; Relaxation laws and the dispersive transport of a group of mobile defects; Illustration showing the relative probabilities of events in the dispersive transport of a pulse of excess charge across a disordered solid's film. INSETS: What happened to the infinity.;Mechanical relaxation.

Discusses the use of penetrating radiation in the measurement of excess carrier lifetime in semiconductors. Assumptions required for the detailed procedure of the photoconductivity decay method; Results of the experiment regarding the scattering of penetrating light; Information on the photocurrent technique of lifetime measurement.

Abstract: The dependence of off-leakage current on channel film quality in poly-Si thin-film transistors has been analyzed using two-dimensional device simulation. It is found that the off-leakage current decreases as the intragrain trap density decreases for the low V gs. This is because the Phonon-assisted tunneling with Poole–Frenkel effect is the dominant mechanism of the carrier generation and the generation rate of carrier pair decreases as the intragrain trap density decreases. On the other hand, the off-leakage current slightly increases as the intragrain trap density decreases for the high V gs. This is because the band-to-band tunneling is the dominant mechanism and the influence of the intragrain trap density to the carrier conductance is larger than that to the generation rate. [Copyright &y& Elsevier]

We introduce single-carrier devices with electrical doped layers as a concept for the characterization of charge-carrier transport in organic semiconductors. In this approach, individual organic layers from a multilayer device are investigated in single-carrier test devices, where they are enclosed by symmetrically arranged electrical doped layers of equal thickness and composition. Single carrier devices without electrical doped layers are usually difficult to interpret due to an uncertainty about interface dipole effects between the metal contacts and pristine organic layers. In comparison, our devices show Ohmic contacts at the electrodes as well as zero built-in voltage and thus allow a more direct insight into charge-carrier transport. State-of-the-art simulation models are applied to analyze current-voltage characteristics and evaluate crucial parameters such as energy barriers between adjacent organic layers and mobilities. [ABSTRACT FROM AUTHOR]

The letter presents a two-dimensional analytical model of the space charge limited (SCL) current injection in a solid with exponentially distributed trap energy state. By considering that the electrons are injected from an infinitely long emission strip of width W, the one-dimensional SCL current density is enhanced by a factor of 1+F(4/π)/(W/L), where F=1/(l+2) measures the mean position of the injected electrons in the solid of length L, and l is the ratio of the distribution of the traps to the free carriers. The analytical formula is verified by using a two-dimensional device simulator. [ABSTRACT FROM AUTHOR]

β-FeOOH nanorods of dimensions of 15 nm diameter and 200 nm length were prepared by aqueous synthesis. Charge carrier dynamics following femtosecond excitation display three time scales. The first is a subpicosecond decay of initially excited carriers to the band edge followed by trapping or nonradiative decay within 2 ps. The trapped electrons and holes persist for significantly longer times (at least tens of picoseconds), similar to previous results from α-Fe2O3 materials. The short carrier lifetimes in these materials are attributed to fast trapping to Fe d-d and midgap states. [ABSTRACT FROM AUTHOR]

p-GaAs/n-GaN heterojunction was fabricated by wafer bonding. Its current-voltage characteristic was systematically investigated at room temperature and at a variety of low temperature. The curves of different temperatures in the logarithmic scales indicate space-charge-limited currents (SCLCs) in the high voltage region (>0.4 V). SCLC current-transport mechanism was confirmed by fitting data. Single-charge injection and the amorphous layer at the bonding interface are presumably the reasons to cause SCLCs. [ABSTRACT FROM AUTHOR]

The first results are reported on the concentration profiles of majority carriers and the effective lifetime profiles of minority carriers in thick (1.6 mm) GaAs plates subjected to surface gettering. It was established that the one- and two-sided coating of the GaAs plates with Y films, followed by heat treatment at 700-800°C, allows a high-resistivity material to be obtained with homogeneous distributions of the electron concentration and the hole lifetime in depth of the semiconductor. [ABSTRACT FROM AUTHOR]

The minority carrier lifetime in boron-doped oxygen-contaminated Czochralski (Cz) silicon is strongly reduced under illumination or carrier injection. This process can be fully reversed by a 200 °C anneal step. In several recent studies it was shown that boron and oxygen are the major components of the underlying metastable Cz-specific defect. The energy level of the defect in its active state A was determined to be around midgap [Schmidt et al., J. Appl. Phys. 86, 3175 (1999)] while the energy level of the defect in its passive state P is very shallow. The Cz-specific defect in its passive state can be identified with the shallow thermal donor. The kinetics of the excess carrier-induced transformation from state P to state A can be described using recombination-enhanced defect reaction theory. On the basis of these experimental facts different solutions for the reduction or elimination of the metastable defect are suggested. Two promising solutions are discussed in more detail: the use of gallium-doped Cz silicon and the introduction of high-temperature anneals into the process sequence. Gallium-doped Cz silicon shows no degradation and excellent lifetimes over a wide resistivity range, although the concentration of interstitial oxygen is in the same range as in standard Cz silicon. Stable solar cell efficiencies comparable to FZ silicon have been achieved. If standard boron-doped Cz silicon is used, the defect concentration can be reduced permanently by a high-temperature anneal using conventional tube or rapid thermal processing. This leads to an improvement of the carrier lifetime by a factor of 2–3. Nevertheless, it is always necessary to use an optimized set of process parameters because otherwise the lifetime of all oxygen-contaminated materials (including gallium-doped Cz silicon) is severely reduced © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is shown that deep trapping of excess carriers in amorphous silicon-carbon films can be used for charge storage applications. Using surface-near pulsed carrier generation ‘‘write,’’ ‘‘read,’’ and ‘‘erase’’ operations are illustrated and charge retention times determined for a set of films with differing carbon contents. [ABSTRACT FROM AUTHOR]

Presents excess carrier lifetimes of several hundred nanoseconds in superlattices grown by photoassisted molecular beam epitaxy. Measurement of quality interfaces by excess carrier lifetime; Reduction of recombination at the superlatticed interface; Achievement of long lifetimes in superlattices.

Carrier decays following pulsed excitation in GaAs-AlGaAs quantum wells have in the past been attributed to an excitonic recombination path. We show here that such an interpretation is inconsistent with the experimental evidence, and that the decays are controlled by recombination through electronic states at the GaAs-AlGaAs interfaces. We discuss the expected magnitude of the decay times and the influence of carrier trapping on the decay process. [ABSTRACT FROM AUTHOR]