Wurtzite ZnSe nanowires: growth, photoluminescence, and single-wire Raman properties

Wurtzite ZnSe nanowires were prepared on GaAs substrates in a metal-organic chemical vapour deposition system. Electron microscopy shows that they are smooth and uniform in size. Both transmission electron microscopy and x-ray diffraction reveal the wurtzite structure of the nanowires, which grows along the [Formula: see text] direction. Raman scattering studies on individual nanowires were performed in the back-scattering geometry at room temperature. Besides the commonly observed longitudinal and transverse optical phonon modes, a possible surface mode located at 233?cm(-1) is also observed in the Raman spectrum. A peak located at 2.841?eV was clearly observed in the photoluminescence spectra of the nanowires, which can be assigned to near band edge emissions of wurtzite ZnSe.     

ZnO nanorods on in-situ synthesized ZnSe grains

The ZnO nanorods grown on in-situ synthesized ZnSe grains through the chemical vapour deposition method are reported here for the first time. With a suitable growth condition, single crystal ZnO nanorods grow on the well-defined bounded facets of the random shape ZnSe grains using Zn and Se powders without any metal catalyst. The growth direction of ZnSe nanorods on a facet of a ZnSe grain is quite uniform. The synthesis mechanism of the ZnO nanorods on the ZnSe grains is proposed. The effects of the Se powder usage on the ZnO-ZnSe products and the photoluminescence of the products are investigated.     

ZnSe晶体的气相法制备和性能研究

采用化学气相输运法,以单质Zn和Se为原料生长ZnSe晶体。比较了加碘(Zn-Se-I2)和未加碘(Zn-Se)两种情况下产物的特征,借助XRD和SEM检测仪器对所生长的ZnSe晶体的结构、形貌和成分进行了分析。结果表明,加入碘后生长的ZnSe晶体为橙黄色,具有较好的结晶性能,晶格常数为5.668nm,Zn与Se的化学成分比为1∶1,没有其它杂质峰;未加碘的产物为多孔状陶瓷,说明加碘可以明显提高ZnSe的结晶性能,解决了一致升华范围较窄的限制条件,避免了ZnSe生长动力学的限制,因此可以获得理想化学计量比的ZnSe晶体。     

Simulating far infrared spectra of Zn1-xMnxSe/GaAs epifilms,MnSe/ZnSe superlattices and predicting impurity modes of N,P defects in Zn1-xMnxSe

A comprehensive lattice dynamical study is reported to emphasize the vibrational behavior of perfect/imperfect zinc-blende (zb) ZnSe, MnSe and Zn_1?xMn_xSe alloys. Low temperature far-infrared (FIR) reflectivity measurements performed on a series of molecular beam epitaxy grown Zn_1?xMn_xSe/GaAs (001) epilayers have a typical ‘intermediate-phonon-mode’ behavior. Besides perceiving ZnSe- and MnSe-like TO-phonon resonances, the study also revealed a weak Mn alloy-disorder mode below MnSe band. A classical effective-medium theory of multilayer optics is used to evaluate dielectric tensors of both epilayers and substrate for simulating reflectivity and transmission spectra of ultrathin epifilms and superlattices at near normal and/or oblique incidence. In the framework of a realistic rigid-ion model and exploiting an average t-matrix Greens function (ATM-GF) theory we appraised the vibrational properties of nitrogen and phosphorous doped Zn-Mn chalcogenides. Lattice relaxations around isolated N_Se (P_Se) defects in ZnSe and zb MnSe are evaluated by first principles bond-orbital model that helped construct perturbation models for simulating the localized vibrational modes (LVMs). Calculated shift of impurity modes for isotopic ¹⁴N_Se (¹⁵N_Se) defects in ZnSe offered a strong revelation of an inflexible defect–host interaction. By retaining force constant change parameter of ¹⁴N_Se (¹⁵N_Se) in heavily N-doped ZnSe, the ATM-GF theory predicted (a) three non-degenerate LVMs for the photoluminescence defect center ^V_Se-Zn-¹⁴N_Se (^V_Se-Zn-¹⁵N_Se) of C_s symmetry, and (b) six impurity modes for the second nearest-neighbor N_Se-Zn-N_Se pair defect of C_2v symmetry. From the range of simulated defect modes, we have ruled out the possibility of N-pairs and justified the presence of V_Se-Zn-N_Se complex centers – likely to be responsible for the observed large absorption bandwidth in highly N-doped ZnSe. High resolution measurements of FIR absorption and/or Raman scattering spectroscopy are needed to validate the accuracy of our theoretical conjectures.     

Observation of Non-Radiative Recombination Enhanced Point Defect Reaction in Semiconductors

IntroductionWide-bandgapcompoundsemiconductorsforblue-greenlaserdiodesandlight-emittingdiodeshavebeenintensivelystudiedinrecentyears.Ithasbeenrecognizedthatpre-existingdefectsplayasignificantroleinthedevicedegradation.Reductionofthesedefectshasbeentheprimaryeffortinachievingalonglifetimeoflight-emittingdevices.Inthispaper,wepresentourmainexperimentalresultsonthenonradiativerecombinationenhancedpointdefectreactioninsemiconductorsbydirectlymonitoringtheprocessofradiativeelectron-holerecombinatio…     

Crystal-chemical models of the defect system in nonstoichiometric and oxygen-doped ZnSe crystals

Quasi-crystal-chemical formulas that take into account the generation of point defects and defect complexes have been proposed for nonstoichiometric, self-doped, and oxygen-doped n- and p-type ZnSe crystals. The defect densities and electron, hole, and Hall carrier concentrations have been evaluated as functions of nonstoichiometry and dopant (Zn, Se, and O) concentration, and conditions have been identified for producing zinc selenide with a given conductivity type and tailored carrier concentration.     

Investigation of intrinsic defects and their distribution in CdSe/ZnSe quantum dot structures

The intrinsic defects and their distribution in CdSe/ZnSe self-assembled quantum dot heterostructures grown under variation of VI/II group beam pressure ratio are investigated by luminescent and high-resolution X-ray diffraction methods. In all samples the self-activated emission connected with donor-acceptor pairs V_Zn–D is found. Analysis of excitation spectra of this band shows that vacancy related defects are mainly localised in ZnCdSe wetting layer. It is found that increase of Se beam pressure results in: (i) the increase of the number of metal vacancy related defects and their appearance on nanoisland interface; (ii) enhancement of Cd/Zn interdiffusion process; (iii) the decrease of Cd content in nanoislands and suppression of nanoisland formation. It is proposed that observed transformation of nanoisland emission band is mainly caused by enhancement of interdiffusion process.     

Study of electroless template synthesized ZnSe nanowires and its characterization

In this work, the successful synthesis of ZnSe nanowires using alumina template by simple and facile electroless template technique has been reported. Morphological characterization of the synthesized nanowires has been done by X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. The optical characterizations were conducted by UV–visible and time resolved photo-luminescence. Grain size of synthesized ZnSe nanowires was also calculated using the XRD results. The calculated crystallite size was found to be 6.80 nm. SEM analysis confirms the fabrication of nanowires successfully and it also confirms the size of the nanowires as per the template parameters. The calculated band gap value of 3.03 eV shows the origin of quantum confinement effect in ZnSe nanowires even at the 100 nm scale. The time resolved photoluminescence result indicates that the ZnSe nanowires can be a promising material for luminescent applications in micro-second time domain.     

Green chemical approaches to ZnSe quantum dots: preparation,characterisation and formation mechanism

ZnSe quantum dots (QDs) and flower-shaped nanocrystals (NCs) were successfully synthesised via a cheap, green and nontoxic route, using environmentally friendly N, N-dimethyl-oleoyl amide as the solvent of Se. The experimental results show that the as-prepared ZnSe QDs with a zinc-blende structure have a narrow size distribution and without resorting to any as-synthetic size-selective procedure. A systematic study of the ZnSe QDs formation process indicates the following properties: variation of some reaction parameters allows us to tune the particle sizes and plays a greater role in the determination of the monodisperse characterisation, for example, these parameters include the amount of ligand and precursors, the injection temperature of Se solution. These size tunabilities interpreted well by the growth kinetics. Another interesting result is that the ZnSe QDs aggregate to flower-shaped NCs, and the flower-shaped NCs also have size-dependence quantum effects as the prepared disperse ZnSe QDs.     

Numerical exploration of plastic deformation mechanisms of copper nanowires with surface defects

Based on the molecular dynamics simulation, plastic deformation mechanisms associated with the zigzag stress curves in perfect and surface defected copper nanowires under uniaxial tension are studied. In our previous study, it has found that the surface defect exerts larger influence than the centro-plane defect, and the 45° surface defect appears as the most influential surface defect. Hence, in this paper, the nanowire with a 45° surface defect is chosen to investigate the defect’s effect to the plastic deformation mechanism of nanowires. We find that during the plastic deformation of both perfect and defected nanowires, decrease regions of the stress curve are accompanied with stacking faults generation and migration activities, but during stress increase, the structure of the nanowire appears almost unchanged. We also observe that surface defects have obvious influence on the nanowire’s plastic deformation mechanisms. In particular, only two sets of slip planes are found to be active and twins are also observed in the defected nanowire.     

The dependence of structural stability and tunable gap on the Si components of ZnSe/Si bi-coaxial nanowire heterostructures

The bare and hydrogen-passivated ZnSe/Si bi-coaxial nanowire heterostructures along [110] direction have been investigated by using the first-principle calculations within density functional theory. The structural stability and electronic property of ZnSe/Si bi-coaxial nanowire heterostructures have been shown by changing the Si components. It is found that the ZnSe/Si nanowires have zero gaps at lower Si components, and then they have the increasing gap at higher Si components. It is seen clearly that there is the transition of band gap form zero to nonzero. With increasing Si components, the ZnSe/Si nanowires can be also achieved as n-type or p-type, in agreement qualitatively with the experimental observations. In addition, the structural stabilities and the cohesive energies of ZnSe/Si bi-coaxial nanowires are changed obviously with the different Si components.     

Inducing imperfections in germanium nanowires

Nanowires with inhomogeneous heterostructures such as polytypes and periodic twin boundaries are interesting due to their potential use as components for optical,electrical,and thermophysical applications.Additionally,the incorporation of metal impurities in semiconductor nanowires could substantially alter their electronic and optical properties.In this highlight article,we review our recent progress and understanding in the deliberate induction of imperfections,in terms of both twin boundaries and additional impurities in germanium nanowires for new/enhanced functionalities.The role of catalysts and catalyst-nanowire interfaces for the growth of engineered nanowires via a three-phase paradigm is explored.Three-phase bottom-up growth is a feasible way to incorporate and engineer imperfections such as crystal defects and impurities in semiconductor nanowires via catalyst and/or interfacial manipulation."Epitaxial defect transfer"process and catalyst-nanowire interfacial engineering are employed to induce twin defects parallel and perpendicular to the nanowire growth axis.By inducing and manipulating twin boundaries in the metal catalysts,twin formation and density are controlled in Ge nanowires.The formation of Ge polytypes is also observed in nanowires for the growth of highly dense lateral twin boundaries.Additionally,metal impurity in the form of Sn is injected and engineered via third-party metal catalysts resulting in above-equilibrium incorporation of Sn adatoms in Ge nanowires.Sn impurities are precipitated into Ge bi-layers during Ge nanowire growth,where the impurity Sn atoms become trapped with the deposition of successive layers,thus giving an extraordinary Sn content (＞6 at.％) in Ge nanowires.A larger amount of Sn impingement (＞9 at.％) is further encouraged by utilizing the eutectic solubility of Sn in Ge along with impurity trapping.     

Structural properties of <111>B -oriented III-V nanowires

Controlled growth of nanowires is an important, emerging research field with many applications in, for example, electronics, photonics, and life sciences. Nanowires of zinc blende crystal structure, grown in the <111>B direction, which is the favoured direction of growth, usually have a large number of twin-plane defects. Such defects limit the performance of optoelectronic nanowire-based devices. To investigate this defect formation, we examine GaP nanowires grown by metal-organic vapour-phase epitaxy. We show that the nanowire segments between the twin planes are of octahedral shape and are terminated by {111} facets, resulting in a microfaceting of the nanowires. We discuss these findings in a nucleation context, where we present an idea on how the twin planes form. This investigation contributes to the understanding of defect formation in nanowires. One future prospect of such knowledge is to determine strategies on how to control the crystallinity of nanowires.     

Analysis of shape and location effects of closely spaced metal loss defects in pressurised pipes

Metal loss due to corrosion is a serious threat to the integrity of pressurised oil and gas transmission pipes. Pipe metal loss defects are found in either single form or in groups (clusters). One of the critical situations arises when two or more defects are spaced close enough to act as a single lengthier defect with respect to the axial direction, causing pipe ruptures rather than leaks, and impacting on the pressure containing capacity of a pipe. There have been few studies conducted to determine the distance needed for defects to interact leading to a failure pressure lower than that when the defects are treated as single defects and not interacting. Despite such efforts, there is no universally agreed defect interaction rule and pipe operators around the world have various rules to pick and choose from. In this work, the effects of defect shape and location on closely spaced defects are analysed using finite element analysis. The numerical results showed that defect shapes and locations have a great influence on the peak stress and its location as well as the failure pressure of pipes containing interacting defects.     

Spectroscopic evidence and control of compensating native defects in doped ZnSe

Electron paramagnetic resonance spectroscopy combined with photoexcitation is used to identify and characterise the defects responsible for the compensation in iodine or aluminium doped ZnSe bulk crystals. The principal g-values of the Al_ZnV_Zn complex are reported for the first time. The acceptor levels of both A-centres observed are determined at 0.50 and 0.54 eV above the valence band edge for I_SeV_Zn and Al_ZnV_Zn, respectively. Annealing of these samples in Zn vapour is shown to be suitable for reproducible adjustments of the electron concentration at room temperature up to a few 10¹⁸ cm⁻³. The tight coupling of these vapour phase equilibrations with the electrical and spectroscopic analysis allows to propose a simple defect-chemical model.     

Effect of point defects and impurities on the electronic transport of Au tipped ultranarrow PbS nanorods

Electronic transport through single nanowire/nanorod directly probes the fundamental limits of semiconductor device miniaturization. Point defects or impurity centers form easily during the growth of nanorods/nanowires which may strongly affect the electronic transport efficiencies. Existing models of electronic transport are often unable to determine the role of defects and impurities at the nanoscale because there are significant differences between nanostructures and bulk materials arising from unique geometries and confinement. The effect of defect and impurities on the conductance of a model ultranarrow PbS rod was modeled using density functional theory. It was observed that the introduction of defects and Au impurities modified the orbital energies of PbS nanorods and reduced the conductance compared to the defect-free rod. The conductance for the nanorods with defects and impurities were limited by the number of available conduction channels required for efficient electronic conduction.     

溶剂热法合成ZnSe纳米材料

以乙酸锌为锌源, Na₂SeO₃•5H₂O或Se粉为硒源, 采用溶剂热法在乙醇胺(EA)溶剂中一步合成晶型和形貌可控的闪锌矿和纤锌矿结构的ZnSe纳米材料。利用X射线衍射(XRD)、能量色散X射线谱 (EDS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对产物的晶型、成分和形貌进行了表征。结果表明, Se源的选取直接决定了ZnSe纳米材料的晶型和形貌: 以Na₂SeO₃•5H₂O为源, 产物为立方相闪锌矿结构的ZnSe纳米颗粒, 直径30 nm左右; 以Se粉为源, 产物为六方相纤锌矿结构的ZnSe纳米片, 厚度约50 nm。进一步的研究表明, 具有合适配位能力的乙醇胺溶剂和Se源对ZnSe纳米结构的合成起重要作用。通过紫外-可见光谱(UV-Vis)和室温光致发光光谱(PL)表征了产物的光学性质。     

Optimum growth of ZnSe film by molecular beam deposition

Zinc selenide (ZnSe) thin film has been grown originally on Coning 7059 glass substrate by molecular beam deposition (MBD). Optimum growth condition has been determined rapidly by comparing and analyzing the relative characteristics of X-ray diffraction spectrum. In this paper, films deposited at different substrate temperatures as a function of Zn/Se beam equivalent pressure (BEP) ratios are investigated. As-grown ZnSe films are polycrystalline and have a cubic (zinc-blende type) structure by the X-ray diffraction technique. The composition of ZnSe film was determined by Energy dispersive spectroscopic (EDS) analysis. Optical properties of ZnSe film were characterized by photoluminescence spectra. Structural parameters such as lattice constant, grain size, strain, dislocation density calculated are correlated with various growth conditions. The dependence of film properties on various substrate temperatures and Se/Zn BEP ratios has been discussed in detail. Finally, high quality of ZnSe film has been successfully obtained and ready for device application.     

Magnetic-field tuning of the alloy-induced disorder in quaternary semimagnetic (Zn, Cd, Mn)Se quantum well structures

The influence of magnetic-field-induced tuning of the disorder on the line width of the lowest excitonic transition in diluted magnetic semiconductor (Zn, Cd, Mn)Se/ZnSe quantum well samples is studied by photoluminescence at 2 K and in magnetic fields up to 7.5 T. It is shown that the dependence of the photoluminescence line width on quantum well thickness can be explained as a sum of contributions of ZnSe barrier, (Zn, Cd, Mn)Se well and the interfaces.     

Doped ZnO nanowires obtained by thermal annealing

Doped ZnO nanowires were prepared in a very simple and inexpensive thermal annealing method using ZnSe nanowires as a precursor. As doped, P doped, and As/P codoped ZnO nanowires were obtained in this method. X-ray diffraction shows that the zincblende ZnSe nanowires were converted to doped wurtzite ZnO nanowires. The incorporation of the dopants was confirmed by energy dispersive X-ray spectroscopy. The doping concentration could be adjusted by changing the annealing temperature and duration. Scanning electron microscopy indicated that the morphology of the ZnSe nanowires was essentially retained after the annealing and doping process. Photoluminescence spectroscopy also verified the incorporation of the dopants into the nanowires.