Electronand Hole Research Articles

Enhancing PFC ability to dye removal and power generation simultaneously via conductive spheres in the anodic chamber

Discharging organic contaminants into the water bodies has become one of the critical problems for the environment. Also, these pollutants are a source of chemical energy. In this study, we introduced a novel photocatalytic fuel cell system with a new design of photoelectrode to treat pollution and produce energy simultaneously. The effect of conductive copper spheres as an electron acceptor to reduce the recombination rate of photogenerated electronsand holes was investigated to improve dye removal, power generation and increase system conductivity. The TiO2/Ti photoanode is designed in a basket for the first time to keep the spheres in the anodic chamber and improve electron transfer through the external circuit. During 5 h, the decolorization of 20 mg/L of methyl orange (MO) reached 86.78%. The short-circuit current, open-circuit voltage, and maximum power density of the PFC were 0.21 mA/cm2, 0.69 V, and 0.033 mW/cm2, respectively. Using conductive spheres improved the system's overall performance by 10%, 23%, and 24%, respectively, compared to when conductive spheres were not used.

Особенности электрофизических параметров кремния, легированного последовательно примесными атомами фосфора и бора

Silicon samples sequentially doped with impurity atoms of phosphorus and boron were studied. These investigations make it possible to study the interaction and distribution of phosphorus and boron impurity atoms in silicon. It has been established that, in such silicon samples, the mobility of electrons and holes changes. From the analysis of the obtained results, it was shown that boron atoms change the type of conductivity of the material to a depth of 2 μm due to the compensation of phosphorus atoms, which are 4 times higher than the concentration of boron in silicon.

Insight into energy level modulation via Mn doping solid solutions for enhanced photocatalytic hydrogen production

Energy level modulationis an effective strategy of increasing the separation efficiency of the photogenerated electrons and holes of sulfide solid solution. In this work, Mn element was introduced to Zn0.5Cd0.5Ssulfide solid solution to modulate energy level of photocatalyst. Compared with pure Zn0.5Cd0.5S, Mn-dopedZn0.5Cd0.5Scaneffectivelyimprove theseparation of photogenerated electronsand holes. As a result, the hydrogen production rateof Mn-doped Zn0.5Cd0.5Sphotocatalystis 4 and 12 timesthan thatofZn0.5Cd0.5S and CdSunder visible-light irradiation. This improvement of photocatalytic activityof Mn-doped Zn0.5Cd0.5Sis attributed to an emerging impurity band, narrow band gap, and negative conduction band after Mn doping. This work providesa rational doping strategy of catalystand a deep insight of the enhancement mechanism of doping effect for photocatalytic reactions.

High-speed and large-responsivity synchronous-traveling carrier photodetector.

A synchronous-traveling carrier photodetector (STC-PD) with a thick absorption region and large diameter is presented and investigated for 100 Gbps PAM4 applications. In the STC structure, a suitable electric field is introduced to synchronize the traveling of electrons and holes, which achieves high bandwidth while maintaining large responsivity. The characteristics of STC-PD, including electric field distribution, energy band diagram, responsivity, junction capacitance, and frequency response, have been studied carefully.

MOF-based Photocatalysts for Hydrogen Production

Metal-organic Frameworks (MOFs) are a class of porous crystalline materials that are assembled by multiple metal ions and organic linkers, featuring high specific surface area and tailorable structures. MOFs exhibit semiconductor-like behavior due to the inorganic fragment in the framework. Principally, the perfect crystalline structure inhibits the formation of charge recombination centers, and their porous characters facilitate the rapid/efficient utilization of the photogenerated electrons and holes. Therefore, in recent years, MOF based materials have received increasing attention for their applications in photocatalysis. Here, starting from the photocatalytic mechanism toward hydrogen production on MOF based materials, the three key photocatalytic processes: Light absorption, electron- hole separation, and surface redox reactions, will be illustrated according to the recent reports. In addition, MOF derivatives for photocatalytic hydrogen production is briefly introduced. Finally, the conclusions and perspectives are provided for the future development of MOF based photocatalysts.

Nanoparticles and Significance of Photocatalytic Nanoparticles in Wastewater Treatment: A Review

Background: In the present situation where there is a water shortage globally, nanoparticles can play a vital role in treating wastewater to make it usable for several processes. Industrial wastewater contains numerous heavy metals and associated wastes that enter our food chain by one means or other. This article provides a review of applications of nanoparticles in wastewater treatment and highlights the significance of photocatalytic nanoparticles in general. Methods: Online journals and books related to wastewater treatment using nanoparticles are reviewed to compile their essentials findings. General mechanisms, applications, limitations, and comparison of photocatalytic nanoparticles are reviewed as well. Results: A study of photocatalytic nanoparticles shows that TiO2 and ZnO nanoparticles have excellent photocatalytic capabilities as compared to other nanoparticles due to their bandgap properties; however, the usage of these nanoparticles is limited since there is higher recombination rate of electrons and holes in photocatalysis. Further, individual limitations also exist as TiO2 is inoperable in the visible light region. So, their heterostructures with other nanoparticles have been developed to overcome their limitations. Other nanoparticles, like noble metals, and those like CuO, CeO2, SnO2 have potential in carrying out photocatalytic degradation of contaminants of wastewaters. Conclusion: Several contaminants can be eliminated from wastewater bodies using photocatalytic nanoparticles. The efficiency of photocatalytic nanoparticles can be enhanced by coupling them with suitable species. Research in this area can prevent the water shortage of upcoming years.

Photoelectrochemical Glucose Biosensor Based on the Heterogeneous Facets of Nanocrystalline TiO2/Au/Glucose Oxidase Films

TiO2 single-crystal nanomaterials with highly reactive surfaces have attracted widespread attention due to their fundamental aspects and industrial applications. However, many previous studies have ignored the poor photoelectric efficiency of TiO2 nanomaterials originating from a mismatch in the diffusion distance of electrons and holes as well as migration rates of holes and electrons. Therefore, suppression of hole migration could enhance the photoelectrochemical performance of TiO2. In this work, single-crystal anatase TiO2 nanomaterials with (001) facets were successfully prepared. The results suggested that some (101) facets were retained by the modified fluoride ion crystal facet control process. Subsequently, fluorine-free and Au-containing crystal facets were obtained by annealing and electrochemical deposition. In addition, the propensity for adsorption of Au on a TiO2 (101) surface was verified by first-principles quantum chemical calculations. Electrochemical impedance spectroscopy and UV–visible spectrophotometry showed the presence of a large area (001), conducive to better enzyme affinity. Biosensors prepared by carrier self-separation derived from natural different facets and Au nanoparticles (TiO2 (001)/Au/GOx) achieved high sensitivities reaching 16.86 μA mM–1 cm–2, an extended linear range (0.01–3 mM), and a low detection limit (0.83 μM). In summary, the proposed route allowed for the first time the use of nanocrystal engineering in the construction of glucose biosensors with satisfactory performances, which is promising for the future fabrication of high-performance biosensors.

Influence of Electron and Hole Distribution on 2T SONOS Embedded NVM

The influence of electron and hole (EH) distribution on two-transistor (2T) silicon-oxide-nitride- oxide-silicon (SONOS) embedded nonvolatile memory (eNVM) is investigated in terms of reliability. As PE (program/erase) cycles are repeated, it is observed that the electron distribution in the nitride layer becomes wider. It leads to the EH distribution mismatch, which degrades the reliability of 2T SONOS eNVM.

Measurement of mobility and lifetime of electrons and holes in a Schottky CdTe diode

We report on the measurement of drift properties of electrons andholes in a CdTe diode grown by the travelling heating method (THM).Mobility and lifetime of both charge carriers has been measuredindependently at room temperature and fixed bias voltage using chargeintegration readout electronics. Both electrode sides of the detectorhave been exposed to a 241Am source in order to obtain eventswith full contributions of either electrons or holes. The drift timehas been measured to obtain the mobility for each charge carrier. TheHecht equation has been employed to evaluate the lifetime. Themeasured values for μτe/h (mobility-lifetime product) are inagreement with earlier published data.

Electroluminescence Characteristics of Inorganic (p-GaN/MgO)-Organic (Alq3) Hybrid p-n Junction Light Emitting Diodes

ABSTRACTInorganic/organic hybrid light-emitting diodes (LEDs) (IO-HyLEDs) composed of p-type GaN/n-type Tris-(8-hydoroxyquinoline) aluminum (Alq3) were fabricated with and without thin MgO electron-blocking layer (EBL) at the inorganic/organic interface. These LEDs showed clear and stable current rectifying diode characteristics and electroluminescence (EL) peaked at UV region at room temperature. For the sample with MgO-EBL, obvious enhancement of green emission from Alq3 layer was observed. This result suggests that due to effective suppression of electron transport from Alq3 to p-GaN by MgO-EBL, radiative recombination of electrons and holes in Alq3 layer was enhanced. It was indicated that the band engineering technique can be applied to control the emission property of inorganic/organic hybrid LED.

Investigation of low-temperature electroluminescence of InGaN/GaN based nanorod lightemitting arrays

For InGaN/GaN based nanorod devices using a top-down etching process, the opticaloutput power is affected by non-radiative recombination due to sidewall defects (whichdecrease light output efficiency) and the mitigated quantum confined Stark effect (QCSE)due to strain relaxation (which increases internal quantum efficiency). Therefore, theexploration of low-temperature optical behaviors of nanorod light emitting diodes(LEDs) will help identify the correlation between these two factors. In this work,low-temperature electroluminescent (EL) spectra of InGaN/GaN nanorod arrays wereexplored and compared with those of planar LEDs. The nanorod LED exhibits amuch higher optical output percentage increase when the temperature decreases.The increase is mainly attributed to the increased carriers in the quantum wellsfor radiative recombination. Also, due to a better spatial overlap of electronsand holes in the quantum wells, the increased number of carriers can be moreefficiently recombined in the nanorod device. Next, while the nanorod array showsnearly constant peak energy in the EL spectra at various injection currents at thetemperature of 300 K, a blue shift has been observed at 190 K. The results suggest thatwith less non-radiative recombination and thus more carriers in the quantumwells, carrier screening and band filling still prevail in the partially strain relaxednanorods. Moreover, when the temperature drops to 77 K, the blue shift of bothnanorod and planar devices disappears and the optical output power decreasessince there are fewer carriers in the quantum wells for radiative recombination.

Bose–Einstein condensation of quasiparticles in graphene

The collective properties of different quasiparticles in various graphene-based structures ina high magnetic field have been studied. We predict Bose–Einstein condensation (BEC)and the superfluidity of 2D spatially indirect magnetoexcitons in a two-layer graphene. Thesuperfluid density and the temperature of the Kosterlitz–Thouless phase transition areshown to be increasing functions of the excitonic density but decreasing functions of amagnetic field and the interlayer separation. The instability of the ground state of theinteracting 2D indirect magnetoexcitons in a slab of superlattice with alternating electronand hole graphene layers (GLs) is established. The stable system of indirect 2Dmagnetobiexcitons, consisting of a pair of indirect excitons with antiparallel dipolemoments, is considered in a graphene superlattice. The superfluid density and thetemperature of the Kosterlitz–Thouless phase transition for magnetobiexcitons in agraphene superlattice are obtained. Moreover, the BEC of excitonic polaritons in a GLembedded in a semiconductor microcavity in a high magnetic field is predicted. While thesuperfluid phase in this magnetoexciton polariton system is absent due to a vanishingmagnetoexciton–magnetoexciton interaction in a single layer in the limit of a high magneticfield, the critical temperature of the BEC formation is calculated. The observation ofthe BEC and superfluidity of 2D quasiparticles in graphene in a high magneticfield would be interesting confirmation of the phenomena we have described.

Long-range migration of intrinsic defects during irradiation or implantation

A series of electron irradiations has been performed on diamond and 4H SiC single crystalspecimens. A wide range of different doses and dose rates was investigated. In addition,a more limited investigation of localized hydrogen and helium implantation of4H SiC has been made. The electron energies were sufficient to cause atomicdisplacements creating vacancies and self-interstitials in the irradiated samples. Afterelectron-irradiation or implantation the samples were studied by low temperature (∼7 K) photoluminescence microscopy. It was found that some of the defect centres migratedover large distances outside of the irradiated regions and that this distance increased withincrease of the dose. Two possible explanations for this remarkable behaviour are discussed.One is based on the absorption by the defects of light created by recombination of electronsand holes in the irradiated or implanted region. The other deals with the consequences ofrecombination-enhanced migration at point defects that traps carriers as they are drivenout of the irradiated region by electric fields created during the irradiation or implantationprocess. Interstitial atoms are deduced as migrating further than vacancies in this process.

Enhanced p-type conductivity and band gap narrowing in heavily Al doped NiO thin filmsdeposited by RF magnetron sputtering

Stoichiometric NiO, a Mott–Hubbard insulator at room temperature,shows p-type electrical conduction due to the introduction ofNi2+ vacancies(VNi′′) andself-doping of Ni3+ ions in the presence of excess oxygen. The electrical conductivity of this important materialis low and not sufficient for active device fabrication. Al doped NiO thin films were synthesizedby radio frequency (RF) magnetron sputtering on glass substrates at a substrate temperature of250 °C in anoxygen + argon atmosphere in order to enhance the p-type electrical conductivity. X-ray diffractionstudies confirmed the correct phase formation and also oriented growth of NiO thin films.Al doping was confirmed by x-ray photoelectron spectroscopic studies. The structural,electrical and optical properties of the films were investigated as a function of Al doping(0–4 wt%) in the target. The room temperature electrical conductivity increased from0.01–0.32 S cm −1 for 0–4% Al doping. With increasing Al doping, above the Mott critical carrier density,energy band gap shrinkage was observed. This was explained by the shift of the band edgesdue to the existence of exchange and correlation energies amongst the electron–electron andhole–hole systems and also by the interaction between the impurity quasi-particle system.

Halide-CVD Growth of Bulk SiC Crystals

A novel approach to the high growth rate Chemical Vapor Deposition of SiC is described. The Halide Chemical Vapor Deposition (HCVD) method uses SiCl4, C3H8 (or CH4), and hydrogen as reactants. The use of halogenated Si source and of separate injection of Si and C precursors allows for preheating of source gases without causing premature chemical reactions. The stoichiometry of HCVD crystals can be controlled by changing the C/Si flow ratio and can be kept constant throughout growth, in contrast to the Physical Vapor Transport technique. HCVD was demonstrated to deposit high crystalline quality, very high purity 4H- and 6H-SiC crystals with growth rates comparable to other bulk SiC growth techniques. The densities of deep electron and hole traps are determined by growth temperature and C/Si ratio and can be as low as that found in standard silane-based CVD epitaxy. At high C/Si flow ratio, the resistivity of HCVD crystals exceeds 105 _cm. These characteristics make HCVD an attractive method to grow SiC for applications in high-frequency and/or high voltage devices.

Symmetry-based calculation of single-particle states and intraband absorption in hexagonalGaN/AlN quantum dot superlattices

We present a symmetry-based method for the efficient calculation of energylevels in hexagonal GaN/AlN quantum dots within the framework of ak·p model. The envelope functions are expanded into a plane wave basis on a hexagonallattice and the group projector method is used to adapt the basis to exploit thesymmetry, resulting in block diagonalization of the corresponding Hamiltonian matrixinto six matrices and classification of the states by the quantum number of totalquasi-angular momentum. The method is applied to the calculation of the electron andhole single-particle states in a quantum dot superlattice. The selection rules forabsorption of electromagnetic waves in the dipole approximation are established andthe intraband optical absorption matrix elements are found. Good agreementwith the available experimental data on intraband optical absorption is found.

Role of rare-earth Ba2+ doping in governing the superconducting and mechanical characteristics of Bi–Sr–Ca–Cu–O

The effect of barium doping on the superconducting and mechanical properties in theBi2Sr2Ca2BaxCu5Oy (BSCCO) system has been investigated by thermoelectric power (TEP),Vickers microhardness (VHN), x-ray diffraction (XRD), and scanningelectron microscope (SEM) analysis. Barium was incorporated withx ranging from 0.0 to 0.82. The temperature variation of the thermopower (Seebeck coefficient)S shows that the critical transition temperatureTc0 is enhanced (to93 K) up to x = 0.45 andthen disappears for x = 0.82. The results have also suggested an increased interaction of electronsand holes with phonons at low temperatures. The enhancement ofTc0 isascribed to the improvement in electric connection between superconducting grains. XRD data show that thehigh-Tc (2:2:2:3) phaseincreases and the low-Tc (2:2:1:2) phase decreases as the barium concentration changes fromx = 0.0 to 0.45. SEManalysis of a sample (x = 0.45) shows that plate-like grains (2223 phase) are formed. Also, an appropriate level ofBa dopant improves the microhardness and fracture toughness remarkably. Theoptimum dopant level of Ba from the point of view of mechanical properties isx = 0.45. The improvement of mechanical characteristics is due to the fact thatBa2+ can fill the intergrain spaces, and thereby reinforce the coupling between granules. From the aboveresults, it is inferred that the added Ba has the positive effect of decomposing the structure of thelow-Tc phase, leadingto the production of BaBiO3 and BaCuO2 andenhancing the high-Tc phase creation.

Doping-Induced Phase Transitions in PolycrystallineLa0.49Sr0.51(Mn1−xNbx)O3

Observations of temperature dependences of ac susceptibilityχac, resistivity (ρ) and dcmagnetization M for polycrystallineLa0.49Sr0.51(Mn1−xNbx)O3(x = 0, 0.05, 0.15, and 0.25) show that due to substitution ofMn4+ by diamagnetic Nb5+, there appear to be(i) the decrease of χac as T>TN, (ii) the occurrence of amaximum (insulator-metal-like transition)for ρ near TC, (iii) the decline of M as x>0.05, and (iv)the lowering of TC. The results might beascribed to: (i) the rearrangement of Mn3+ andMn4+ ions, (ii) the decrease of the number ofMn3+ and Mn4+ pairs involved in doubleexchange interaction, (iii) the delocalization of the electrons andholes, (iv) the reduction of the randomness of the delocalized carrierscattering by thermal spin fluctuation due to magnetic ordering, and(v) the compensation effect of Nb5+ ions forSr2+ ions.

Radiation induced defects in Sr2B5O9Br:Ce3+ storage phosphor

Radiation induced defects in polycrystalline pure andCe3+ dopedSr2B5O9Br storagephosphors have been investigated using EPR and optical absorption methods. The EPR of irradiatedpure Sr2B5O9Br represents two overlapping spectra in the 335–340 mT range from paramagnetic electron andhole trapping centres, which are stable at room temperature. These centres are attributed toF(Br−) and OBr− centres, i.e. an electron trapped in a bromine vacancy and a hole trapped on an oxygen ionat a bromine site. The transitions of F(Br−) centres cause the optical absorption band at 560 nm. Another observedabsorption band at 365 nm was attributed to the transitions ofO− centres. Thus electron and hole trapping in pureSr2B5O9Br occursin VBr and OBr2− aggregates, which are created during the synthesis.EPR and optical absorption measurements onCe3+ doped Sr2B5O9Br reveal similar defects as in pure material. It is very likely that the same defects take part inthe processes of thermally and photo-stimulated luminescence.

Multiphonon resonant Raman scattering in the semimagneticsemiconductor Cd1−xMnxTe:Fröhlich and deformation potential exciton–phonon interaction

A theory describing multiphonon resonant Raman scattering (MPRRS)processes in wide-gap diluted magnetic semiconductors is presented,with Cd1−xMnxTeas an example. The incident radiation frequency ωl istaken above the fundamental absorption region. The photoexcited electron andhole make real transitions through the LO phonon, when one considers Fröhlich (F)and deformation potential (DP) interactions. The strong exchange interaction,typical of these materials, leads to a large spin splitting of the exciton states inthe magnetic field. Neglecting Landau quantization, this Zeeman splittinggives rise to the formation of eight bands (two conduction and six valenceones) and ten different exciton states according to the polarization of theincident light. Explicit expressions for the MPRRS intensity of secondand third order, the indirect creation and annihilation probabilities, theexciton lifetime, and the probabilities of transition between different excitonstates and different types of exciton as a function of ωl andthe external magnetic field are presented. The selection rules for all hot excitontransitions via exciton–photon interaction and F and DP exciton–phononinteractions are investigated. The exciton energies, as a function ofB, the Mnconcentration x, andthe temperature T,are compared to a theoretical expression. Graphics for creation and annihilationprobabilities, lifetime, and Raman intensity of second and third order arediscussed.