Lifetime Of Nonequilibrium Charge Carriers Research Articles

Photoluminescence of GaPNAs/GaP(N) superlattices and bulk GaPN layers on GaP substrates

The addition of a few percent of nitrogen to GaP or GaPAs allows obtaining GaPNAs solid solutions that are lattice-matched to the silicon substrate over a wide range of band gaps, which makes it possible to obtain optoelectronic silicon integrated circuits. However, materials with a small fraction of nitrogen are understudied due to the difficulty in epitaxial growth of quaternary solid solutions with three materials of group V. The purpose of the study was the investigation of the influence of the substrate temperature during the epitaxial growth of dilute nitride materials (GaPN solid solution and GaPNAs/GaP(N) superlattices) on their optical properties, as well as the influence of the growth temperature and superlattice design on the bandgap of the resulting material. It was shown that there is an optimal growth temperature for samples: at temperatures below the optimal, non-radiative recombination at defects predominates, and at a temperature higher than the optimal one, the solid solution of the GaPN layer material decomposes into components with a larger and smaller fraction of nitrogen. Studies were also carried out on the decay of photoluminescence intensity over time in the studied structures at room temperature, which allowed us to evaluate the influence of growth parameters and structure design on the lifetime of nonequilibrium charge carriers. The best lifetime for structures with superlattices was obtained for the GaPNAs/GaPN superlattice and amounted to ~0.2 ns. As a result, the optimal growth temperatures were determined for bulk GaPN layers and for GaPNAs/GaP(N) superlattices, which leads to an increase in the PL intensity and lifetime of the carrier

Kinetics of Carrier Lifetime Degradation in High‐Temperature 1 MeV Electron‐Irradiated Cz n‐Si Associated with the Formation of Divacancy‐Oxygen Defects

Kinetics of degradation of the nonequilibrium charge carrier lifetime (τ) in Czochralski‐grown (Cz) n‐Si irradiated with 1 MeV electrons at different temperatures in the range from 20 to 285 °C are experimentally and theoretically investigated. It is established that changes in τ are qualitatively and quantitatively determined by the temperature of electron irradiation. Analysis of experimental data using the Shockley‐Read‐Hall (SRH) theory shows that the formation of recombinationally active divacancy‐oxygen (V2O) and vacancy‐oxygen (VO) complexes is the main mechanism of τ degradation in this experiment.

Effect of Gamma Irradiation on Electrophysical Parameters of Silicon Solar Cells Doped with Nickel

The results of the studies of changes in the electro-physical parameters (Voc – no-load voltage, Isc – short-circuit current density; τ – lifetime of nonequilibrium charge carriers) of photocells made on plates of monocrystalline silicon of the p-type conductivity with the specific resistance ρ 0.5 Ohm cm, doped with nickel, under irradiation with γ-quanta from 60Co source are presented. It is shown that the efficiency of the solar energy conversion in nickel-doped photovoltaic cells remains higher than in standard cells up to irradiation doses of 108 rad. It was established that with increasing diffusion temperature of nickel atoms radiation stability of electrophysical parameters of photovoltaic cells also increases. A decrease in the concentration of recombination-active radiation defects is due to the getterization by nickel atoms of technological (background) impurities and the action of nickel clusters as effluents for radiation-induced vacancies.

OPTICALLY PUMPED BIPOLAR TRANSISTOR

The properties of a bipolar npn transistor were studied when exposed to unmodulated incoherent radiation created by a “white” LED. The static and dynamic characteristics of the transistor were measured at various exposure intensities. It is shown that the change in the characteristics of the transistor under optical influence is due to an increase in the lifetime of nonequilibrium charge carriers and the photovoltaic effect in p-n junctions. For these reasons, the gain increases, the switching threshold decreases, and the transistor speed increases. The results obtained are applicable both to the creation of high-speed transistors and integrated circuits of a fundamentally new type.

Nonlinear Inertial Diode Model Considering the Dependence of Nonequilibrium Charge Carrier Lifetime on Direct Current to Improve Simulation of Radioelectronic Equipment

Introduction. Adequate modeling of semiconductor devices with a p–n-junction in reverse bias represents a relevant research problem. The existing quasistatic and non-quasistatic models fail to provide a satisfactory description for the dependence of nonequilibrium charge carrier lifetime on current density. This leads to significant simulation errors (tens of percent) at pulsed broadband signals. Simulation errors arise, because the existing models regard the lifetime as a constant value.Aim. To propose and investigate an equivalent circuit of a p–n-junction considering the dependence of the lifetime of nonequilibrium charge carriers on direct current, with the possibility of its simple integration into CAD.Materials and methods. The study was carried out on the example of a fast recovery silicon diode BAS16J with a p–n-junction manufactured by Nexperia. A modified diode model is proposed in the form of an equivalent circuit that considers the dependence of the lifetime of nonequilibrium charge carriers on the direct current of the p–njunction at high injection levels.Results. The discrepancy between the experimental and simulated curves did not exceed ±9 % under pulsed diode operation. The extraction of parameters in the proposed model is carried out conventionally, from the current-voltage and capacitance-voltage characteristics of the diode.Conclusion. The proposed non-quasistatic equivalent diode circuit can be used when designing radio electronic devices operated at short-pulse broadband signals. The proposed diode model can be easily implemented in modern CAD systems at the user level.

Impurity-impurity interaction during the growth of UMG-Si-based mc-Si

This article investigates the relationship between the chemical composition and electrophysical properties of p- and n-type multicrystalline silicon ingots based on metallurgical silicon with a purity of 99.99 at.%. In particular, the role of impurity-impurity interactions in the production of multisilicon by the Bridgman vertical method is evaluated in order to identify approaches to controlling this process effectively. The phase equilibrium calculations in the “silicon–all impurities” and “silicon-impurity-oxygen” systems were carried out based on the Gibbs energy minimization in the Selector software package. The study investigates the rank correlations of the concentrations of various impurities with each other, as well as with the specified electrical resistivity (SER) and the lifetime of nonequilibrium charge carriers (NCC) in the direction of crystal growth. Pair correlations of the element distribution profiles were considered based on the role of the main factor represented by the ratio of individual impurity solubilities in solid or liquid silicon (k0), as well as from the standpoint of direct interaction between two elements. It was found that the k0 value for two individual impurities in silicon does not automatically lead to the pair correlation of their distribution profiles in the ingot. A significant effect on the distribution profiles of impurities in multisilicon with k0→0 has the factor of binding some part of the impurity into such a form that this impurity can be incorporated easily into a growing crystal. Binding may be induced by the interaction of the impurity in the melt with the oxygen background, its segregation at the grain boundaries, and its capture by the crystallization front in the composition of the liquid inclusion. Significant correlations of impurity distribution profiles in the ingot were demonstrated by the pairs whose elements interact without the formation of chemical compounds in the 25–1413 °C temperature range. The conducted phase equilibrium calculations for the “silicon–all impurities” system revealed the possibility of forming the VB2, TiB2, ZrB2, and MgTiO4 solid phases in the melt.

Влияние никеля на время жизни носителей заряда в кремниевых солнечных элементах

It has been shown experimentally that nickel clusters on the surface of a silicon sample contain a large amount of oxygen and recombination impurities - Cu, Fe, Cr, which shows good gettering properties of clusters. The optimum temperature of nickel diffusion into silicon is determined - Т=800-850 ° С. Doping with impurity nickel atoms with the formation of clusters makes it possible to increase the lifetime of nonequilibrium charge carriers in the base of a solar cell by up to 2 times, while the formation of a nickel-enriched region in the face layer is more efficient. It is shown that the effect of additional doping with nickel weakly depends on the sequence of the processes of nickel diffusion and the creation of a working p–n-junction.

Effect of nickel on the lifetime of charge carriers in silicon solar cells

It has been shown experimentally that nickel clusters on the surface of a silicon sample contain a large amount of oxygen and recombination impurities --- Cu, Fe, Cr, and so shows good gettering properties of clusters. The optimum temperature of nickel diffusion into silicon is determined as 800-850oC. Doping with impurity nickel atoms with the formation of clusters makes it possible to increase the lifetime of nonequilibrium charge carriers in the base of a solar cell by up to 2 times, while the formation of a nickel-enriched region in the face layer is more efficient. It is shown that the effect of additional doping with nickel weakly depends on the sequence of the processes of nickel diffusion and the creation of a working p-n-junction. Keywords: silicon solar cells, nickel diffusion, nonequilibrium charge carriers, gettering, p-n junction.

Lifetime Control in Irradiated and Annealed Cz n‐Si: Role of Divacancy‐Oxygen Defects

The behavior of the nonequilibrium charge carrier lifetime (τ) in Czochralski‐grown (Cz) n‐Si after a low‐dose 60Co gamma or 1 MeV electron irradiation and subsequent annealing are investigated. Irradiated samples with different doping levels (free‐electron concentration n0 ≈ 1014−1016 cm−3) are isochronally annealed at temperatures between 20 and 380 °C. It is found that τ significantly decreases after annealing in the range ≈180–280 °C, and this effect is stronger in low‐resistivity n‐Si. It is shown that change in τ in the annealing range of 180–380 °C is caused by the divacancy‐oxygen (V2O) complexes. The Shockley–Read–Hall (SRH) theory is used to describe the experimental data. It is determined that the V2O formation is characterized by the activation energy of 1.24 ± 0.04 eV and the frequency factor of (1 ± 0.5) × 109 s−1, and their annealing is characterized by the activation energy of 1.54 ± 0.09 eV and the frequency factor of (2.9 ± 0.6) × 1010 s−1. The values of hole capture cross‐section (σp) by the single‐ and double‐charged acceptor states of V2O are obtained as (5 ± 2) × 10−13 and (8 ± 4) × 10−12 cm2, respectively.

Influence of Divacancy-Oxygen Defects on Recombination Properties of n-Si Subjected to Irradiation and Subsequent Annealing

The variation of recombination properties in n-Si grown by the Czochralski method, doped to the free electron concentration n0 ∼ 10^14 ÷10^16 cm^−3, irradiated with 60Co y-quanta or 1-MeV electrons, and isochronously annealed for 20 min in the temperature interval 180–380∘C, in which divacancy-oxygen (V2O) complexes are formed and annealed, has been studied in detail. The nonequilibrium charge carrier lifetime т is found to significantly decrease after the annealing in a temperature interval from 180 to 280∘C, with the effect being stronger for low-resistive n-Si. It is shown that a change in т after the annealing at 180–380∘C is caused by divacancy defects, most probably V2O. By analyzing the experimental data with the help of the Shockley–Read–Hall statistics, it is found that the formation of V2O defects is characterized by an activation energy of 1.25±0.05 eV and a frequency factor of (1±0.5)×10^9 s^−1, and their annealing by an activation energy of 1.54±0.09 eV and a frequency factor of (2.1±1.4)×10^10 s^−1. The values of the hole capture cross-sections by singly and doubly charged acceptor states of V2O are obtained as: (5±2)×10^−13 and (8±4)×10^−12 cm^2, respectively.

Crystal stacking: A route to control photoelectrochemical behavior of BiOBr films

Two types of BiOBr thin films with substantially different crystal stacking and photoelectrochemical (PEC) properties were grown on conducting ITO substrates. In the first case, electrophoretically deposited closely-packed layers with parallel arrangement of (001) faceted plate crystallites (BiOBr||) exhibit p-type PEC behavior in Br2/Br− aqueous solution generating cathodic photocurrent under electrochemical polarization. In the second case, BiOBr electrodes composed of plates with predominant perpendicular orientation to the ITO surface (BiOBr⊥) demonstrate opposite PEC behavior and generate anodic photocurrent. This fundamental difference in PEC properties of BiOBr⊥ and BiOBr|| photoelectrodes, which have close values of BET specific surface area (25 and 18 m2/g), plate thickness (15 and 16 nm) and comparable non-equilibrium charge carrier lifetime (in a sub-ns range), is explained by different stacking of plate crystals in them. Since BiOBr has better electronic conductivity within the (001) plane compared to that along the [001] direction, BiOBr⊥ crystallites have better electrical contact with ITO and are subjected to electrochemical polarization, while BiOBr|| crystallites are predominantly in an open circuit condition and their properties are influenced by the boundaries between plate crystals.

SEPARATE DETERMINATION OF THE PHOTOELECTRIC PARAMETERS OF THE BASE REGION OF N+−P(N)−P+ SILICON STRUCTURE BY NONCONTACT METHOD BASED ON QUANTUM EFfi CIENCY RELATION MEASUREMENTS AT TWO WAVELENGTHS

A noncontact method for the determination of recombination parameters of p(n) layer local ranges of silicon n+−p(n)−p+ structures is considered. The method is based on local illumination of the investigated structure by two different absorbed light beams. Initially both beams illuminate simultaneously one side of the local range of this structure and then another side. The intensities оf the light beams are modulated at one frequency so the alternative photo−voltage becomes equal to zero. In this case the short current regime is established for its alternating component. As a consequence the nonilluminated parts of the structure do not shunt its illuminated part. The ratios of the light beam intensities are measured under these conditions. In this work we calculated nomograms for separate determination of the nonequilibrium charge carrier lifetime of the illuminated p(n) local space and its surface recombination velocity using the measured intensity ratios. The calculations were performed at low injection level for one dimensional case. The nomograms were calculated at wave lengths of 1064 and 808 nm for various thicknesses of the n+−p(n)−p+ structures and various modulation frequencies. It was found that the nomograms almost do not depend on the modulation frequency if the live time of the nonequilibrium charge carriers is less than the modulation period. Furthermore, we observed that the nomograms shift substantially and change their shape for thin structures if the diffusion time of nonquilibrium charge carriers from the rear side of the structure to its face side becomes less than their lifetime. In this case the nomograms may be only used for the determination of the surface recombination velocity of the nonquilibrium charge carriers at the rear side of the structure.

On the Problem of Determining the Bulk Lifetime by Photoconductivity Decay on the Unpassivated Samples of Monocrystalline Silicon

In the indirect band gap semiconductors, and in particular, in silicon, the lifetime of nonequilibrium charge carriers is determined by recombination through impurity centers and it is inversely proportional to their concentration. Therefore, this is the most important parameter for determining the quality of the material. The noncontact methods of its measurement, in particular, the noncontact measurements of the decay of the photoconductivity (PC) constant, are the most important ones. The surface recombination strongly influences the shape of the curve. The calculation of the lifetime in the bulk by the decay constant remains relevant since there is no single-valued analytic solution of the continuity equation for this case. In the samples of monocrystalline silicon with unpassivated surfaces, the relaxation of PC is analyzed by numerical methods. The applicability of the known formulas for estimating the contribution of surface recombination to the effective PC relaxation time is discussed. It is shown that the period of time for which the fast exponents disappear depends on the relative thickness of the sample to be measured. The effective decay time is determined by the maximum value of the surface component of the relaxation time and is described by wellknown formulas only in this piece of the relaxation curve. The effective relaxation time attains saturation by the time when the signal intensity reaches 45% of the maximum value (the origin of the effective decay time according to the recommendation of the SEMI MF 1535 standard) only for the samples with a thickness of less than 3–5 diffusion lengths. For larger thicknesses, the contribution of the fast exponents to the effective PC relaxation time is observed right up to 5% of the maximum signal (i.e., until reaching the noise level of the signal to be measured). In this case using the recommended by SEMI MF 1535 standard formulas leads to a sufficiently large systematic error (up to 20%) in evaluating the free charge carrier’s lifetime.

Eu modified Cu2O thin films: Significant enhancement in efficiency of photoelectrochemical processes through suppression of charge carrier recombination

We propose a simple way to increase incident photon-to-current conversion efficiency (IPCE, Y) for electrodeposited p-type Cu2O films through addition of Eu(III) to the electrodeposition bath. This is the first reported enhancement of photocurrent for Cu2O modified with a rare-earth element. Our study is based on hypothesis that a large ionic radius of Eu(III) promotes its precipitation in form of inclusions of another phase, which act as getter centers leading to purification of host material from detrimental impurities and, correspondingly, to increase in lifetime of non-equilibrium charge carriers. SEM, EDX and XRD analyses indicate that addition of Eu(III) results in some increase of Cu2O crystallite size and growth of a secondary Eu containing phase without changing the Cu2O lattice parameters. Electrochemical impedance spectroscopy indicates invariance of acceptor concentration and flat band potential for Eu modified films. Remarkable increase of charge carriers’ lifetime, which manifests in the growth of Cu2O exciton photoluminescence (PL) intensity and PL decay constant, leads to increased IPCE for the Eu modified films. Optimization of Eu(III) concentration in the electrodeposition bath allows attaining the cathodic photocurrent as high as 3.2 mA cm−2 (35 mW cm−2 Xe lamp illumination), which is as ≈40% greater than that for the pure Cu2O film and corresponds to Y ≈ 100% at wavelength λ < 450 nm.

Two-photon confocal microscopy as a tool for nonequilibrium charge-carrier lifetime tomography in semiconductor materials

By the example of ZnSe crystals, the capabilities of two-photon confocal microscopy as a tool for obtaining “planar” maps of nonequilibrium charge-carrier lifetimes in semiconductor materials and for investigating other direct-gap semiconductors and semiconductor heterostructures are considered. It is shown that such maps with a depth step and an in-plane resolution of several microns can be obtained for distances from the surface up to 1 mm. This technique is used to visualize inhomogeneities in the crystals under study and to examine their structure and luminescence characteristics.

Microwave photoconductivity of bifacial silicon solar cells of p + nn + type under laser irradiation

The microwave photoconductivity of silicon solar cells under laser irradiation has been investigated. It is shown that shunting of the solar cell region exposed to light by the rest of the cell may reduce significantly the relaxation time of microwave photoconductivity in comparison with the nonequilibrium charge carrier lifetime in the base region.

Measurement of lifetime of nonequilibrium charge carriers in single-crystal silicon

An equation of continuity describing decay of nonequilibrium charge carriers after illumination of semiconducting silicon by a long duration pulse of light with wavelength of 1.06 µm is solved by numerical methods in a one-dimensional approximation. It is shown that, when the volume recombination lifetime of minority carriers is 500 µs and higher, the known formula for “thin” samples 1/τeff = 1/τV + 2s/d cannot be used to evaluate the effective lifetime of thin plates (10 µm or above). Estimations of the range of variation of excess density in which the instantaneous lifetime achieves saturation are carried out; this takes place in the second part of the relaxation curve if the wafer thickness does not exceed three diffusion lengths of minority carriers. It is demonstrated that the formula scaled to an infinite recombination rate is applicable for thicknesses of the sample within the range from one to five diffusion lengths. For higher thicknesses, it is necessary to apply corrections taking into account the dependence of instantaneous lifetime on the excess density of nonequilibrium charge carriers.

Temperature Dependence of Minority Carrier Lifetime in Epitaxially Grown p&lt;sup&gt;+&lt;/sup&gt;-p&lt;sup&gt;–&lt;/sup&gt;-n&lt;sup&gt;+&lt;/sup&gt; 4H-SiC Drift Step Recovery Diodes

In this paper we report on the effect of temperature and injection level on the effective lifetime of non-equilibrium charge carriers in p-base of 4H-SiC PiN diodes. Studies were carried out on 1kV drift step recovery diodes (DSRDs) with p+-p--n+. The lifetime of non-equilibrium charge carriers in 4H-SiC p+-p--n+ structures increases by an average of 6 times from 250ns to 1.4μs with the increase of the samples temperature from 300K to 673K. However, increase of the injection level in the drift region from 2.3·1016cm-3 to 5.9·1016cm-3 does not affect the lifetime indicating that Shockley-Read-Hall recombination processes are dominating.

Temperature dependence of the lifetime of nonequilibrium charge carriers in GaP diodes under condition of recombination current domination

Temperature dependence of the lifetime of nonequilibrium charge carriers limited by recombination process in a p-n junction space-charge region has been obtained from current–voltage, capacitance–voltage and thermometric characteristics of GaP p+-n junctions in the temperature range 150–500 K. The results have been refined using the data of the junction relaxation characteristics. Parameters of the carriers' lifetime sensitivity to the temperature and current have been determined. It has been established that the charge carriers recombine predominantly through deep single-level amphoteric-type centres. The depth of the centres makes approx. (EC-1.25 eV). We suppose that the nature of the centres formation is not connected with the junction fabrication technology. It has rather fundamental origin. The results of the present investigation could be used in the development of devices based on wide bandgap semiconductors and particularly high temperature diode sensors.

Influence of impurities and conditions of growing the silicon single crystals by Czochralski method on the value of lifetime of non-equilibrium charge carriers

В работе исследуется влияние содержащихся в монокристаллическом кремнии таких примесей, как кислород, углерод, бор, а также скорости охлаждения выращиваемого монокристалла на время жизни неравновесных носителей заряда. Установлено, что повышение концентрации кислорода и бора способствует увеличению времени жизни неравновесных носителей заряда, а увеличение концентрации углерода и скорости охлаждения монокристалла кремния ведет к уменьшению времени жизни неравновесных носителей заряда.