ZnSe Grains Research Articles

Combustion synthesis of ZnSe with strong red emission

A fast and furnace-free way is reported to synthesize ZnSe from self-sustained combustion reaction between Zn and Se. The synthesized ZnSe shows a zincblende structure and large particle size of >100μm, which can be reduced by two magnitude to 1.4μm by using NaCl as diluent. It is proposed that the added NaCl can lower the reaction temperature and diminish the interfacial area of ZnSe grains by a steric hindrance effect. The ZnSe samples show the characteristic band-edge absorption in visible region, and the band gap energy is estimated to be 2.43–2.58eV. Under an ultraviolet excitation, the ZnSe samples do not show the near-band-edge blue emission but exhibit strong red emission, which is likely related to the intrinsic point defects in ZnSe. Compared with previous studies, the ZnSe samples synthesized in this work show red emission peaks at even larger wavelength up to 730nm.

Atom probe tomography study of internal interfaces in Cu2ZnSnSe4 thin-films

We report on atom probe tomography studies of the composition at internal interfaces in Cu2ZnSnSe4 thin-films. For Cu2ZnSnSe4 precursors, which are deposited at 320 °C under Zn-rich conditions, grain boundaries are found to be enriched with Cu irrespective of whether Cu-poor or Cu-rich growth conditions are chosen. Cu2ZnSnSe4 grains are found to be Cu-poor and excess Cu atoms are found to be accumulated at grain boundaries. In addition, nanometer-sized ZnSe grains are detected at or near grain boundaries. The compositions at grain boundaries show different trends after annealing at 500 °C. Grain boundaries in the annealed absorber films, which are free of impurities, are Cu-, Sn-, and Se-depleted and Zn-enriched. This is attributed to dissolution of ZnSe at the Cu-enriched grain boundaries during annealing. Furthermore, some of the grain boundaries of the absorbers are enriched with Na and K atoms, stemming from the soda-lime glass substrate. Such grain boundaries show no or only small changes in composition of the matrix elements. Na and K impurities are also partly segregated at some of the Cu2ZnSnSe4/ZnSe interfaces in the absorber, whereas for the precursors, only Na was detected at such phase boundaries possibly due to a higher diffusivity of Na compared to K. Possible effects of the detected compositional fluctuations on cell performance are discussed.

Optoelectronic study and annealing stability of room temperature pulsed laser ablated ZnSe polycrystalline thin films

In principal, we described stability of the room temperature ZnSe thin films with thermal annealing deposited onto glass by pulsed laser deposition technique using third harmonic 355nm of Nd: YAG laser beam. Optoelectronic analysis and stability with thermal annealing was described in terms of structural and optical properties. These properties were investigated via X-ray diffraction, atomic force microscope, scanning electron microscope, Raman, Fourier transform infrared and photoluminescence spectroscopies. From the strong reflection corresponding to the (111) plane (2θ=27.48°) and the longitudinal optical “LO” phonon modes at 250cm−1 and 500cm−1 in the X-ray diffraction and Raman spectra, a polycrystalline zincblende structure of the film was established. At 300 and 350°C annealing temperatures, the film crystallites were preferentially oriented with the (111) plane parallel to the substrate and became amorphous at 400°C. Atomic force microscopic images showed that the morphologies of ZnSe films became smooth with root mean squared roughness 9.86nm after annealing at 300 and 350°C while a rougher surface was observed for the amorphous film at 400°C. Fourier transform infrared study illustrated the chemical nature and Zn–Se bonding in the deposited films. For the as-deposited and annealed samples at 300 and 350°C, scanning electron micrographs revealed mono-dispersed indistinguishable ZnSe grains and smooth morphological structure which changed to a cracking and bumpy surface after annealing at 400°C. The physical phenomenon of annealing induced morphological changes could be explained in terms of “structure zone model”. Excitonic emission at 456nm was observed for both as-deposited and annealed film at 350°C. The transmission spectrum shows oscillatory behavior because of the thin film interference and exhibited a high degree of transparency down to a wavelength ~500nm in the IR region. Energy band-gap was increased from 2.65eV to 2.7eV for the annealed crystalline film at 350°C which was further decreased to 2.56eV for the annealed amorphous film at 400°C. The observed results manifested that room temperature pulsed laser ablated ZnSe thin film showed excellent structural, optical and morphological stability up 350°C for optoelectronic applications.

The effect of Zn excess on kesterite solar cells

Accuracy in composition control has been one of the top issues for fabricating high-performance kesterite (Cu2ZnSn(Se,S)4) solar cells. A detailed understanding of the effect of Zn excess on device performance has not yet been demonstrated. Thus, specific criteria for high-performance devices, in particular discriminating between the effects of Zn-rich features at the front versus the back of the absorber, are desired. In this study, we report that co-evaporated kesterite absorbers can demonstrate high device efficiency despite the presence of large quantities of ZnSe. However, the benign presence of ZnSe is found to be conditional. While large ZnSe grains on the back of the absorbers are not harmful to device performance, the ZnSe grains produced by excess Zn near the end of the deposition degrade the cell efficiency from 8% level to 6% level (without anti-reflection coatings). The other effect related to excess Zn on the front of absorber is the facilitation of breakdown in lower reverse bias. The breakdown indicated here occurs only under the illumination of blue photons, and to our best knowledge has not been reported before. The exact mechanism of the breakdown remains open, but it is demonstrated to be related to the photoconductivity of CdS, and is thus possibly a symptom of lateral defect issues in the absorber, caused by the overdose of Zn. The same type of issue contributing to the breakdown may also be responsible for part of the parasitic loses at the working voltage, and therefore warrants further research.

Zinc Blende 구조를 가지는 ZnSe 결정의 밴드 특성에 관한 연구

ZnSe, as a II-VI compound semiconductor which has a wide band gap in the visible region is applicable to the various fields such as laser diode, display and solar cell. By using the electrochemical deposition method, ZnSe thin film was synthesized on the ITO glass substrate. The synthesis of ZnSe grains and their structure having zinc blende shape were verified through the analysis of XRD and SEM. UV spectrophotometric method determined the band gap as the value of 2.76 eV. Applying the DFT (Density Functional Theory) in the molecular dynamics, the band structure of ZnSe grains was analyzed. For ZnSe grains with zinc blende structure, the band structure and its density of state were simulated using LDA (Local Density Approximation), PBE (Perdew Burke Ernzerhof), and B3LYP (Becke, 3-parameter, Lee-Yang-Parr) functionals. Among the calculations of energy band gap upon each functional, the simulated one of 2.65 eV based on the B3LYP functional was mostly near by the experimental measurement.

Raman Scattering from ZnSe Nanolayers

A series of ZnSe single layers having thickness between 30 nm and 1 μm was deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in high vacuum has been applied. Moreover, SiOx/ZnSe periodic multilayers prepared by the same deposition technique and having ZnSe layer thickness of 2 and 4 nm have been studied. Raman spectra were measured at 295 K, using the 442 nm line of a He–Cd laser as well as different lines of the Ar or Ar/Kr lasers. The observed Raman features have been related to multiple optical phonon (1LO to 4LO) light scattering and connected with the existence of randomly oriented crystalline ZnSe grains in both ZnSe single layers and ZnSe layers of the multilayers. Relatively large line width (≈ 15 cm−1) of the 1LO band has been observed and related to lattice distortion in the crystalline grains and existence of amorphous phase in the layers thinner than 100 nm. The Raman spectra measured on both ZnSe single layers and SiOx/ZnSe multilayers using the 488 nm line with a gradually increased laser beam power indicate an increased crystallinity at high irradiation levels.

CVD Grown Zinc Based Nanostructures on Zinc Selenide Microscale Grains

With a suitable growth condition using CVD method, 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. To our best knowledge, there is no report in growing ZnO nanostructures on in-situ synthesized ZnSe. The growth direction of ZnSe nanorods on a facet of a ZnSe grain is quiet uniform. The growth mechanism of the nanostructure will be discussed. Meanwhile, the photoluminescence of the nanostructures will be investigated.

Characterization and growth mechanism of ZnSe microspheres prepared by hydrothermal synthesis

ZnSe microspheres have been prepared in NaOH aqueous solution at 150 °C for 24 h by hydrothermal synthesis using Zn and Se as source materials. Effect of Zn/Se on the morphologies of ZnSe was studied. High ratio of Zn/Se was critical to prepare ZnSe microspheres and only tiny ZnSe grains were derived when Zn/Se was less than 2. The ZnSe microspheres were formed by the attached growth of ZnSe nuclei on the surface of Zn cores while the ZnSe grains were synthesized by the free growth of the nuclei in hydrothermal solution without sustainment.

ZnO nanorod synthesis from Zn‐based II–VI semiconductors

AbstractIn this paper, we report the synthesis of ZnO nanorods on in‐situ grown ZnSe grains by using the simple chemical vapor deposition (CVD) method and elementary sources of Zn and Se. To our best knowledge, there is no report of growing other Zn‐based nanostructures on in‐situ synthesized ZnSe. The ZnO–ZnSe system has the advantage of carrier transfer between the two binary II–VI semiconductors with different energy levels for device applications [1], which cannot be achieved in the single‐compound semiconductor nanostructures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Self-catalytic ZnSe nanorods on grains synthesized using thermal evaporation method

In this paper, ZnSe nanorods grown on in-situ synthesized ZnSe grains are reported. The ZnSe products are synthesized through thermal evaporation of elementary materials of Zn and Se powders in a horizontal resistance furnace. It is interesting to note that the ZnSe nanorods of nearly the same diameter and length are obtained, and they grow in the same direction on a facet of the ZnSe grain. The ZnSe grains are random in shape, with well-defined bounded facets. The ZnSe grains can be synthesized in various growth conditions while the ZnSe nanorods can be synthesized on the ZnSe grains with the fulfillment of the Zn enriched condition. The growth of ZnSe nanorods can be described by the self-catalytic vapor–liquid–solid (VLS) mechanism.