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Electro-optical properties of diluted GaAsN on GaAs grown by APMOVPE

Abstract

In this paper we report on the optical and electrical studies of single GaAs1−x Nx epitaxial layers grown on GaAs substrates by means of atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). Three kinds of samples with 1.2 %, 1.6 % and 2.7 % nitrogen content were studied. Optical properties of the layers were investigated with the use of room temperature transmittance and reflectance measurements. Subsequently Schottky Au-GaAs1−x Nx contacts were processed and characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements within 80–480 K temperature range. From the I-V and C-V characteristics the ideality factor, series resistance and built-in potential were determined. Obtained diodes can be used for further studies on defects with the use of DLTS method.

Open access
A new porphyrin sensitizer with phenolic binding group for high efficiency dye-sensitized solar cells

Abstract

A novel zinc porphyrin (5,10,15-tri-dodecoxyphenyl-20-(4-hydroxyphenyl-azo-benzenyl)-porphyrinatozinc (tdhab-ZnP)) with benzenyl-azo-phenolic group, able to adsorb on the nanocrystalline-TiO2 film, has been synthesized. We constructed a dye-sensitized solar cell based on the nanocrystalline-TiO2 hierarchical structure film, with a power conversion efficiency of 4.15 % and a high current density of 14 mA/cm2 under AM 1.5 irradiation. UV-Vis absorption spectra measurements indicated that the tdhab-ZnP molecules formed a charge transfer complex with TiO2 nanoparticles (NPs) through the phenolic group. Cyclic voltammetry measurement showed that the charge separation resulting from the tdhab-ZnP excited singlet state to the conduction band (CB) of TiO2 and charge shifting from the I−/I3− couple to the porphyrin radical cation were thermodynamically feasible.

Open access
Structural and optical characteristics of SnS thin film prepared by SILAR

Abstract

SnS thin films were grown on glass substrates by a simple route named successive ion layer adsorption and reaction (SILAR) method. The films were prepared using tin chloride as tin (Sn) source and ammonium sulfide as sulphur (S) source. The structural, optical and morphological study was done using XRD, FESEM, FT-IR and UV-Vis spectrophotometer. XRD measurement confirmed the presence of orthorhombic phase. Particle size estimated from XRD was about 45 nm which fitted well with the FESEM measurement. The value of band gap was about 1.63 eV indicating that SnS can be used as an important material for thin film solar cells. The surface morphology showed a smooth, homogenous film over the substrate. Characteristic stretching vibration mode of SnS was observed in the absorption band of FT-IR spectrum. The electrical activation energy was about 0.306 eV.

Open access
Optical properties of AlN layers obtained by magnetron sputtering

Abstract

The growth of AlN layers on glass substrates using magnetron sputtering method was performed and the grown layers were subjected to optical measurements. Transmission spectra of the layers grown at different content of N2 in the atmosphere were obtained. The transmission spectra as well as energy gap depended on N2 content. The annealing of the layers in air led to transmission changes and influenced energy gap and refractive index values.

Open access
Temperature dependence of Bi4Ge3O12 photoluminescence spectra

Abstract

Bi4Ge3O12 single crystals were obtained using Czochralski growth method. Photoluminescence spectra were analyzed versus temperature from 12 to 295 K. Besides the previously observed emission bands at 610 and 820 nm, the new emission band at 475 nm was found by a careful temperature dependence measurement in the present study. The influence of basic and defect structure on the shape and position of the spectra versus temperature was discussed.

Open access
Influence of thermal treatment on the formation of ohmic contacts based on Ti/Al/Ni/Au metallization to n-type AlGaN/GaN heterostructures

Abstract

Interfacial reactions between Ti/Al/Ni/Au metallization and GaN(cap)/AlGaN/GaN heterostructures at various annealing temperatures ranging from 715 to 865 °C were studied. Electrical current-voltage (I–V) characteristics, van der Pauw Hall mobility measurements and surface topography measurement with atomic force microscopy (AFM) were performed. The ohmic metallizations were annealed at various temperatures in a rapid thermal annealing system and the annealing time of 60 seconds was kept for all samples. To study the influence of the parameters of annealing process on the properties of the 2 dimensional electron gas (2DEG) the van der Pauw Hall mobility measurement was used. Interfacial reactions between the contact metals and heterostructures were analyzed through depth profiles of secondary ion mass spectroscopy. It was observed that transition from nonlinear to linear I-V behavior occurred after the annealing at 805 °C. For the studied samples, the most promising results were obtained for the annealing temperature of 805 °C. This temperatue ensured not only low contact resistance but also made possible to preserve the 2DEG.

Open access
Antireflective bilayer coatings based on Al2O3 film for UV region

Abstract

Bilayer antireflective coatings consisting of aluminium oxide Al2O3/MgF2 and Al2O3/SiO2 are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5 × 10-3 Pa in the presence of oxygen, and magnesium fluoride was prepared by thermal evaporation on heated optical lenses made from quartz glass (Corning HPFS). Substrate temperature was maintained at 250 _C during the deposition. Thickness and deposition rate were controlled with a thickness measuring system Inficon XTC/2. The experimental results of the optical measurements carried out during and after the deposition process have been presented. Physical thickness measurements were made during the deposition process and resulted in 44 nm/52 nm for Al2O3/MgF2 and 44 nm/50 nm for Al2O3/SiO2 system. Optimization was carried out for ultraviolet region with minimum of reflectance at 300 nm. The influence of post deposition annealing on the crystal structure was determined by X-ray measurements. In the range from ultraviolet to the beginning of visible region, the reflectance of both systems decreased and reached minimum at 290 nm. The value of reflectance at this point, for the coating Al2O3/MgF2 was equal to R290nm = 0.6 % and for Al2O3/SiO2R290nm = 1.1 %. Despite the difference between these values both are sufficient for applications in the UV optical systems for medicine and UV laser technology.

Open access
Structural, optical and electrical characterization of CBD synthesized CdO thin films: influence of deposition time

Abstract

Cadmium oxide (CdO) thin films were grown on glass substrates by chemical bath deposition (CBD) method for different deposition times using cadmium acetate as cationic precursor. The structural and optical characterization was carried out using XRD, TEM, and UV-Vis spectrophotometer measurements. Structural analyses with XRD confirmed cubic structure of the CdO. Average particle size estimated from Rietveld refinement method of XRD pattern corresponded well with TEM measurement. The optical band gap varied between 2.35 eV to 2.48 eV with deposition time and an increase in optical band gap with decreasing film thickness was observed. The AC electrical conduction behavior of the CdO film was investigated as a function of temperature as well as frequency. The conductivity measurements indicated localized conduction and hopping of carriers between localized states. The value of real part of dielectric constant was found to decrease with frequency and increase with temperature. The Nyquist plots at different temperatures showed the existence of both grains and grain boundaries contributing to conduction mechanism.

Open access
Characterization of CuO/n-Si heterojunction solar cells produced by thermal evaporation

Abstract

Copper(II) oxide (CuO) in powder form was evaporated thermally on the front surface of an n-Si (1 0 0) single crystal using a vacuum coating unit. Structural investigation of the deposited CuO film was made using X-ray difraction (XRD) and energy dispersive X-ray analysis (EDX) techniques. It was determined from the obtained results that the copper oxide films exhibited single-phase CuO properties in a monoclinic crystal structure. Transmittance measurement of the CuO film was performed by a UV-Vis spectrophotometer. Band gap energy of the film was determined as 1.74 eV under indirect band gap assumption. Current-voltage (I-V) measurements of the CuO/n-Si heterojunctions were performed under illumination and in the dark to reveal the photovoltaic and electrical properties of the produced samples. From the I-V measurements, it was revealed that the CuO/n-Si heterojunctions produced by thermal evaporation exibit excellent rectifying properties in dark and photovoltaic properties under illumination. Conversion efficiencies of the CuO/n-Si solar cells are comparable to those of CuO/n-Si produced by other methods described in the literature.

Open access
Nanostructured device based on coated ZnO layer as a window in solar cell applications

Abstract

This work highlights some physical properties related to the influence of aluminum, tin and copper incorporation on nanostructured zinc oxide (ZnO:M; M:Al, Sn and Cu) thin films prepared by ultrasonic spray pyrolysis technique (USP) on glass substrate at 350±5 °C. For the as-grown layers, M- to Zn-ratio was fixed at 1.5 %. The effects of metal doping on structural, morphological, optical and electrical properties were investigated. X-ray diffraction pattern revealed that the as-prepared thin films crystallized in hexagonal structure with (0 0 2) preferred orientation. The surface topography of the films was performed by atomic force microscopy. AFM images revealed inhibition of grain growth due to the doping elements incorporation into ZnO matrix, which induced the formation of ZnO nanoparticles. Optical measurements showed a high transparency around 90 % in visible range. Some optical parameters, such as optical band gap, Urbach energy, refractive index, extinction coeffi-cient and dielectric constant were studied in terms of doping element. Particularly, dispersion of refractive index was discussed in terms of both Cauchy and single oscillator model proposed by Wemple and DiDomenico. Cauchy parameters and single oscillator energy E0 as well as dispersion energy Ed were calculated. Finally, electrical properties were investigated by means of electrical conductivity and Hall effect measurements. The measurements confirmed n type conductivity of the prepared thin films and a good agreement between the resistivity values and the oxidation number of doping element. The main aim of this work was the selection of the best candidate for doping ZnO for optoelectronics applications. The comparative study of M doped ZnO (M:Al, Sn and Cu) was performed. High rectifying efficiency of the Al/n-ZnO/p-Si/Al device was achieved and non-ideal behavior was revealed with n > 4.

Open access