Diffraction Properties and Application of 3D Polymer Woodpile Photonic Crystal Structure

We present a new technique for modification of diffraction and optical properties of photonic devices by surface application of polymer Three-Dimensional (3D) woodpile Photonic Crystal (PhC) structure. Woodpile structure based on IP-Dip polymer was designed and fabricated by Direct Laser Writing (DLW) lithography method based on nonlinear Two-Photon Absorption (TPA). At first, we investigated diffraction properties of woodpile structure with a period of 2 μm. The structure was placed on a glass substrate, and diffraction patterns were measured using laser sources with different wavelengths. After diffraction properties investigation, the fabricated structures were used in optoelectronic devices by their surface application. Our polymer 3D PhC woodpile structures were used for radiation properties modification of light emitting devices - optical fiber and Light Emitting Diode (LED) and for angular photoresponse modification of InGaAsN-based photodiode. The modification of the far-field radiation patterns of optical fiber and LED and spatial modulation of light coupling into photodiode chip with applied structures were measured by goniophotometer. Quality of fabricated structures was analyzed by a Scanning Electron Microscope (SEM)

Properties of Mechanochemically Synthesized Famatinite Cu3SbS4 Nanocrystals

In this study, we report the optoelectric and thermoelectric properties of famatinite Cu3SbS4 that was mechanochemically synthesized in a planetary mill from powder elements for 120 min in an inert atmosphere. The tetragonal famatinite Cu3SbS4 was nanocrystalline with a crystallite size of 14 nm, as endorsed by Rietveld refinement. High-resolution transmission electron microscopy showed several crystallites in the range of 20–50 nm. Raman spectroscopy proved the purity of the synthesized famatinite Cu3SbS4 and chemical-state characterization performed by X-ray photoelectron spectroscopy confirmed that the prepared sample was pure. The Cu1+, Sb5+, and S2− oxidation states in Cu3SbS4 sample were approved. The morphology characterization showed homogeneity of the prepared sample. The photoresponse of Cu3SbS4 was confirmed from I–V measurements in the dark and under illumination. The photocurrent increase reached 20% compared to the current in the dark at a voltage of 5 V. The achieved results confirm that synthesized famatinite Cu3SbS4 can be applied as a suitable absorbent material in solar cells. The performed thermoelectric measurements revealed a figure of merit ZT of 0.05 at 600 K

Composition related electrical active defect states of InGaAs and GaAsN

This paper discusses results of electrically active defect states - deep energy level analysis in InGaAs and GaAsN undoped semiconductor structures grown for solar cell applications. Main attention is focused on composition and growth condition dependent impurities and the investigation of their possible origins. For this purpose a widely utilized spectroscopy method, Deep Level Transient Fourier Spectroscopy, was utilized. The most significant responses of each sample labelled as InG2, InG3 and NG1, NG2 were discussed in detail and confirmed by simulations and literature data. The presence of a possible dual conduction type and dual state defect complex, dependent on the In/N composition, is reported. Beneficial characteristics of specific indium and nitrogen concentrations capable of eliminating or reducing certain point defects and dislocations are stated

AP-MOVPE Technology and Characterization of InGaAsN p-i-n Subcell for InGaAsN/GaAs Tandem Solar Cell

Tandem (two p-n junctions connected by tunnel junction) and multijunction solar cells (MJSCs) based on AIIIBV semiconductor compounds and alloys are the most effective photovoltaic devices. Record efficiency of the MJSCs exceeds 44% under concentrated sunlight. Individual subcells connected in series by tunnel junctions are crucial components of these devices. In this paper we present atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE) of InGaAsN based subcell for InGaAsN/GaAs tandem solar cell. The parameters of epitaxial structure (optical and electrical), fabrication process of the test solar cell devices and current-voltage (J-V) characteristics are presented and discussed

Nanostructure and magnetic anomaly of mechanosynthesized Ce1−x_{1-x}Yx_{x}O2−δ_{2-δ} (x ≤ 0.3) solid solutions

Electromagnetic properties of complex oxide solid solutions containing Ce and Y attract increasing interests due to their high application potential. Their properties are known to be dependent on many factors including grain size and crystal defects. Here we focus on unique features of nanocrystalline Ce$_{1-x}$Y$_{x}$O$_{2-δ}$ (x ≤ 0.3) solid solutions prepared via a mechanosynthesis. Mechanically activated CeO$_{2-δ}$ and mechanosynthesized Ce$_{1-x}$Y$_{x}$O$_{2-δ}$ exhibit room-temperature ferromagnetism. The saturation magnetization reaches maximum for the Ce$_{0.9}$Y$_{0.1}$O$_{2-δ}$ solid solution. XPS and Raman spectra show that Ce$^{Zahl}$4+s are partially reduced to Ce$^{3+}$, with simultaneous introduction of oxygen vacancies accumulated on surface of the solid solutions. An analysis of the experimental magnetization data and the determination of both the spin state and the concentration of magnetic carriers revealed that a small part of the Ce$^{3+}$ spins (<1%) is responsible for the magnetic state of the Ce$_{1-x}$Y$_{x}$O$_{2-δ}$ system. Existence of clusters with a short-range antiferromagnetic order is also suspected

Theoretical and Experimental Substractions of Device Temperature Determination Utilizing I-V Characterization Applied on AlGaN/GaN HEMT

A differential analysis of electrical attributes, including the temperature profile and trapping phenomena is introduced using a device analytical spatial electrical model. The resultant current difference caused by the applied voltage variation is divided into isothermal and thermal sections, corresponding to the instantaneous time- or temperature-dependent change. The average temperature relevance is explained in the theoretical section with respect to the thermal profile and major parameters of the device at the operating point. An ambient temperature variation method has been used to determine device average temperature under quasi-static state and pulse operation, was compared with respect to the threshold voltage shift of a high-electron-mobility transistor (HEMT). The experimental sections presents theoretical subtractions of average channel temperature determination including trapping phenomena adapted for the AlGaN/GaN HEMT. The theoretical results found using the analytical model, allow for the consolidation of specific methodologies for further research to determine the device temperature based on spatially distributed and averaged parameters

Mechanochemical Synthesis and Characterization of CuInS2/ZnS Nanocrystals

In this study, CuInS2/ZnS nanocrystals were synthesized by a two-step mechanochemical synthesis for the first time. In the first step, tetragonal CuInS2 was prepared from copper, indium and sulphur precursors. The obtained CuInS2 was further co-milled with zinc acetate dihydrate and sodium sulphide nonahydrate as precursors for cubic ZnS. Structural characterization of the CuInS2/ZnS nanocrystals was performed by X-ray diffraction analysis, Raman spectroscopy and transmission electron microscopy. Specific surface area of the product (86 m2/g) was measured by low-temperature nitrogen adsorption method and zeta potential of the particles dispersed in water was calculated from measurements of their electrophoretic mobility. Optical properties of the nanocrystals were determined using photoluminescence emission spectroscopy

Synthesis and characterization of CuInS2 nanocrystalline semiconductor prepared by high-energy milling

Nanocrystalline CuInS particles have been synthesized from copper, indium, and sulfur powders by high-energy milling in a planetary mill in an argon atmosphere. Structural characterization of the prepared nanoparticles, including phase identification, Raman spectroscopy, specific surface area measurement, and particle size analysis were performed. The optical properties were studied using UV–Vis absorption and photoluminescence (PL) spectroscopy. The production of CuInS (JCPDS 027-0159) particles with a crystallite size of about 17.5–23.5 nm was confirmed by X-ray diffraction. The crystal structure has a tetragonal body-centered symmetry belonging to the I-42d space group. The Raman spectra also proved the formation of pure CuInS nanoparticles. TEM and HRTEM measurements revealed the presence of nanoparticles of different dimensions (10–20 nm) and their tendency to form agglomerates. The nanoparticles tend to agglomerate due to their large specific surface area. The average size of the synthesized particles was determined by photon cross-correlation spectroscopy to be in the range of 330–530 nm (bimodal size distribution). The band gap of the CuInS particles is 2 eV which is wider than that in bulk materials. The decrease in size leads to the blue-shift of the PL spectra. Therefore, CuInS nanoparticles are promising candidates for optical applications, and they have high potential in solar energy conversion.The support through the Slovak Grant Agency VEGA (projects 2/0027/14, 1/0439/13, 2/0051/14) and APVV 14-0103 is gratefully acknowledged. The authors also acknowledge the support of the European Union through the CT-2011-1-REGPOT285895 AL-NANOFUN project (Advanced Laboratory for the Nano-Analysis of novel Functional materials), for the microscopy facilities sited at the Institute of Materials Science in Seville

Comparative study of ZnO thin film prepared by pulsed laser deposition - Comparison of influence of different ablative lasers

Článek se zabývá transparentními vodivými oxidy na bázi ZnO, které byly připraveny pulsní laserovou depozicí (PLD) a jejich různými vlastnostmi, které jsou porovnány v rozsahu aplikovaných ablačních laserů: (1) pevnolátkový Nd:YAG laser pracující s třetí harmonickou (vlnová délka 355 nm, 15 ns délka pulzu a 10 Hz pulzní frekvence) a (2) excimerový laser pracující s KrF plynnou směsí (248 nm, 20 ns and 10 Hz). První část se zabývá vlivem tlaku kyslíku na krystalografické parametry nedopovaných tenkých vrstev ZnO. Jako optimální byl vybrán tlak v rozmezí 2 až 5 Pa. Navíc byl zkoumán vliv různých dopovacích prvků, hliníku a galia, v daném prostředí. Výsledky ukázaly, že male množství (cca 0,15 hmotnostního %) Al (nebo Ga), podstatně zlepšilo koncentraci nosičů náboje s adekvátním snížením resistivity. Dále byly zkoumány optické vlastnosti – propustnost a šířka zakázaného pásu. Srovnání použitých laserů odhalilo v podstatě pozitivní vliv na elektrické vlastnosti pro excimerový laser.The contribution deals with transparent conductive oxides based on ZnO, which were prepared by Pulsed Laser Deposition (PLD) and their different properties are compared in the scope of the applied ablating lasers: (1) a solid state Nd:YAG laser working at third harmonic generation (wavelength 355 nm, 15 ns pulse length and 10 Hz pulsing frequency) and (2) an excimer laser working with KrF gas composition (248 nm, 20 ns and 10 Hz). The first part of the study deals with the influence of the oxygen pressure on crystallographic parameters of undoped ZnO films and the pressure interval between 2 and 5 Pa was assessed as an optimum. Moreover, the influence of different doping elements, aluminum and gallium, respectively, were analyzed. The results showed that a small amount (∼0.15% wt. content) of Al (or Ga, respectively) substantially improved carrier concentration with adequate resistivity decrease. Furthermore, optical properties: – transmittances and energy band-gap shift were investigated. Comparison between applied lasers revealed a substantially positive effect on electrical properties for the excimer laser