Utilization In Optoelectronic Devices Research Articles

Nanostructured SnS2 Thin Films from Laser Ablated Nanocolloids: Structure, Morphology, Optoelectronic and Electrochemical Properties.

Tin disulfide (SnS2 ) is a binary chalcogenide semiconductor having applications in solar cells, energy storage, and optoelectronics. SnS2 thin films were deposited by spraying the nanocolloids synthesized by pulsed laser ablation in liquid. The structure, morphology, and optoelectronic properties were studied for films obtained from two liquid media (ethanol and isopropanol) and after heat treatments at various temperatures. X-ray diffraction analysis confirmed the hexagonal crystal structure of the films, whereas the 2-H polytype structure was identified by micro-Raman spectroscopy. Oxidation states of Sn (4+) and S (2-) identified from high resolution X-ray photoelectron spectra confirmed the composition and chemical states of the films. The SnS2 thin films exhibited distinct porous surface morphologies as the liquid medium in laser ablation was varied. All as-prepared and annealed films showed photoluminescence with a high intensity peak at 485 nm and a low intensity peak at 545 nm. Thin films annealed at 300 °C showed improved electrochemical properties upon illumination using a blue LED light source. Current-voltage curves recorded in dark and light as well as the photoresponse measurements showed their suitability for utilization in optoelectronic devices. The results of this study may trigger further research towards fabrication of nanostructured thin films in large area for optoelectronic and photoelectrochemical applications in an environment friendly and cost-effective way.

Structural, optical absorption and photoluminescence spectral studies of Sm3+ ions in Alkaline-Earth Boro Tellurite glasses

Sm3+ ions doped Alkaline-Earth Boro Tellurite (AEBT) glasses were prepared by using conventional melt quenching technique and characterized using the spectroscopic techniques such as FT-IR, optical absorption, emission and decay spectral measurements to understand their utility in optoelectronic devices. From absorption spectra, the bonding parameters, nephelauxetic ratios were determined to know the nature of bonding between Sm3+ ions and its surrounding ligands. From the measured oscillator strengths, the Judd-Ofelt (J-O) intensity parameters were evaluated and in turn used to estimate various radiative parameters for the fluorescent levels of Sm3+ ions in AEBT glasses. The PL spectra of Sm3+ ions exhibit three emission bands corresponding to the transitions 4G5/2 → 6H5/2, 6H7/2 and 6H9/2 in the visible region for which the emission cross-sections and branching ratios were evaluated. The decay spectral profiles measured for 4G5/2 → 6H7/2 transition showed single exponential for lower concentration and non-exponential for higher concentration of doped rare earth ion in the as prepared glasses. Conversion of decay spectral profiles from single to non-exponential have been analyzed using Inokuti–Hirayama (I–H) model to understand the energy transfer mechanism involved in the decay process. CIE Chromaticity coordinates were measured using emission spectral data to identify the exact region of emission from the as-prepared glasses. From the evaluated radiative parameters, emission cross-sections and quantum efficiencies, it was observed that AEBT glass with 1 mol% of Sm3+ ions is more suitable for designing optoelectronic devices.

Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red Light-Emitting Diodes.

Although halide perovskite nanocrystals (NCs) are promising materials for optoelectronic devices, they suffer severely from chemical and phase instabilities. Moreover, the common capping ligands like oleic acid and oleylamine that encapsulate the NCs will form an insulating layer, precluding their utility in optoelectronic devices. To overcome these limitations, we develop a postsynthesis passivation process for CsPbI3 NCs by using a bidentate ligand, namely 2,2'-iminodibenzoic acid. Our passivated NCs exhibit narrow red photoluminescence with exceptional quantum yield (close to unity) and substantially improved stability. The passivated NCs enabled us to realize red light-emitting diodes (LEDs) with 5.02% external quantum efficiency and 748 cd/m2 luminance, surpassing by far LEDs made from the nonpassivated NCs.

Mobility enhancement of CVD graphene by spatially correlated charges

We present a strategy for enhancing the carrier mobility of single layer CVD graphene (CVD SLG) based on spatially correlated charges. Our Monte Carlo simulations, numerical modeling and the experimental results confirm that spatial correlation between defects with opposite charges can provide a means to control independently the carrier concentration and mobility of planar field effect transistors in which graphene is decorated with a layer of colloidal quantum dots (QDs). We show that the spatial correlation between electrically charged scattering centres close to the graphene/SiO2 interface and the localised charges in a QD layer can smooth out the electrostatic potential landscape, thus reducing scattering and enhancing the carrier mobility. The QD capping molecules influence the distribution and correlation of electrical charges in the vicinity of SLG and provide a means of tuning the carrier concentration and increasing the carrier mobility in graphene. These results represent a significant conceptual advance and provide a novel strategy for control of the electronic properties of 2D materials that could accelerate their utilization in optoelectronic devices.

Full-potential calculations of structural and optoelectronic properties of cubic indium gallium arsenide semiconductor alloys

In this work, the first-principle calculations have been performed to predict the structural, electronic and optical properties of cubic InxGa1−xAs for 0≤x≤1, using 16-atom within the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method based on Density Functional Theory (DFT) as implemented in WIEN2k computational code. The Local Density Approximation (LDA) and Wu–Cohen Generalized Gradient Approximation (WC–GGA) were employed as the exchange–correlation term to calculate the structural and electronic properties. Moreover, the Engel–Vosko GGA (EV-GGA) and the recently modified semi–local Becke–Johnson (mBJ) functional were also used to compute the electronic and optical properties in order to get some better degree of precision. The real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient and optical conductivity were calculated to discuss the linear optical properties of InxGa1−xAs alloys. The achieved results show a great potential utilization in optoelectronic devices especially in infrared applications.

Theoretical investigation of band gap and optical properties of ZnO1−xTex alloys (x = 0, 0.25, 0.5, 0.75 and 1)

In this study, the special quasi-random structure (SQS) approach has been considered for structural, electronic and optical properties of rock-salt (RS) and zinc-blende (ZB) phases of ZnO1−xTex (x=0, 0.25, 0.5, 0.75 and 1) using density functional theory. The Wu–Cohen generalized gradient approximation (GGA) has been employed for optimizing the lattice parameters (a0) and bulk moduli (B0) in both phases which show reasonable agreement with numerous theoretical and experimental results. To compute the band gaps with high degree of precision, we employed Engel–Vosko GGA and modified Becke and Johnson local density approximation (mBJLDA) functionals. In the RS phase, metallic nature of the compounds under investigation is evident for 0.25<x<1, whereas direct band gap appears at all concentrations in ZB phase. The density of states (total and partial) are presented to comprehensively analyze the electronic structure of all compounds. Contrary to earlier theoretical studies, the mBJLDA band gap values for the end binaries appear to be significantly improved showing overall better agreement with the experimental data. The optical properties of ZnO1−xTex alloys in the ZB phase are also discussed in terms of dielectric function which show their potential utilization in optoelectronic devices.

Evaluation of electrical conductivity and thermal diffusivity of vanadyl naphthalocyanine

Metal phthalocyanines have attracted much attention because of their potential application in electronic devices, optical data storage, photoconductors and sensors [1, 2]. They are also very good candidates for high density optical data recording (ODR) media due to their thermal and chemical stability and facility for synthetic modification. An essential requirement for the ODR material is the long wavelength absorption. Metal naphthalocyanines absorb at a longer wavelength than the phthalocyanines because of their additional benzoannulation [3]. For constructing practical ODR devices the thermal properties of the organic dyes are of considerable importance [4–7]. It is also necessary to investigate the electrical properties of metal naphthalocyanines prior to their utilization in optoelectronic devices. Although there are a number of reports on the optical properties of metal naphthalocyanines [8, 9], only very few investigations are found on the electrical properties of these interesting materials. In the present study, we report the electrical conductivity and thermal diffusivity of pristine and iodine doped vanadyl naphthalocyanine (VONc). VONc was synthesized and purified by the method reported by Yanagi et al. [9]. The compound was characterized by elemental analysis, IR and electronic spectra. The data were in good agreement with those reported in the literature [3]. VONc was doped with iodine in the solution phase [10, 11] by stirring 100 mg of powdered sample with a saturated solution of iodine in carbon tetrachloride for 48 h. The doped material was filtered and washed with carbon tetrachloride to remove excess iodine. The iodine doped vanadyl naphthalocyanine (VONcI) was dried at 360 K in vacuo for 2 h. The pellet samples of 5.0 mm diameter and 0.8 mm thickness were prepared at a pressure of 2000 kg cm−2. The electrical conductivity was measured in a shielded cell under dynamic vacuum in the temperature range 100–450 K using a Keithley model 617 electrometer. The samples studied were heated to 375 K and cooled to ambient temperature before measurement, to avoid the interference of moisture and adsorbed oxygen. A photoacoustic method was used to measure the thermal diffusivity of the pellet samples (see Fig. 1). The light source used was a 488 nm radiation from an Ar+ laser (Liconix-5000 series) at a power level of 30 mW. The laser beam was chopped by a mechanical chopper (Stanford Research System model SR 540). By varying the chopping rate the characteristic frequency ( fc) was determined by front surface illumination of the sample. The Arrhenius plot of the temperature dependence of electrical conductivity (σ ) for VONc and VONcI are shown in the Fig. 2. In the pristine sample, the temperature dependence is very weak below 300 K. Above this temperature the behavior is in accordance with an Arrhenius relationship. The increase in conductivity at higher temperature must be due to an enhancement in carrier density with increase in thermal energy. The activation energies at different temperature ranges are given in Table I. The electrical conductivity of vanadyl naphthalocyanine increases when doped with iodine. The behavior of VONcI indicates that considerable changes have