Band Gap Of PbS Research Articles

Studies on Lead Sulphide (PbS) Thin Film Prepared by Chemical Bath Deposition Method

Lead Sulphide, PbS thin films deposited on glass substrates by a chemical bath deposition method, which is a simple and easily controlled technique. The reactive substances used to obtain the PbS layers were (Pb(NO3)2), NaOH, Sc(NH2)2 and H2O for different dipping concentrations of lead nitrate, dipping times and temperatures. The films were structurally characterized by X-ray diffraction studies. The films are very adherent to the substrate and well crystallized according to the face centered cubic structure with the preferred orientation (1 1 1). The films were optically characterized by the transmission and reflectance spectrum, examined by a UV – VIS Spectrophotometer. In the infrared range, low transmittance and reflectance are detected (between 10% and 30%), while there is no transmittance or reflectance in the UV and visible regions. It can be seen from absorption spectra that absorption is stronger in the UV and UV-VIS region and gradually diminishes. Maximum absorption is observed in the visible and ultraviolet range, which indicates that the film prepared is of nanocrystalline. The band gap of PbS can be varied in the range of 0.41 to 2.71 eV, which is a significant material feature and opens the door to a new class of applications. The calculated band gap was determined to be between 1.88eV and 2.1eV.

Stable Ta2O5 nanotubes decorated by PbS by the SILAR method for photocatalytic dye degradation

Tantalum oxide Ta2O5 nanotubes (NTs) were prepared by electrochemical anodization and were decorated with lead sulfide nanoparticles PbS (NPs) by Successive Ionic Layer Adsorption and Reaction commonly known as the SILAR method. The PbS NPs/Ta2O5 NTs were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Transmission Electron Spectroscopy (TEM), Photoluminescence (PL), and Diffuse Reflectance Spectroscopy (DRS). An increasing number of SILAR cycles applied on this substrate were shown to induce a variation in the optical properties and the bandgap of PbS NPs/Ta2O5 NTs. The bandgap went from 3.83 eV for bare Ta2O5 to 3.4 eV for Ta2O5 NTs decorated with 10 PbS SILAR cycles. Ten SILAR cycles were seen to correspond to 2.7 wt% and 1.4 M percentage of the decorated Ta2O5 NTs. Ten SILAR cycles were required to drive the fastest degradation kinetics of the Black Amido mediating Ta2O5 (NTs)-PbS NPs under light irradiation. However, longer SILAR cycles were not seen to faster the degradation kinetics due to light screening. The prepared nanotubes exhibited high stability over 5 photocatalytic reuse cycles.

PbS and PbO Thin Films via E-Beam Evaporation: Morphology, Structure, and Electrical Properties.

Thin films of lead sulfide (PbS) are being extensively used for the fabrication of optoelectronic devices for commercial and military applications. In the present work, PbS films were fabricated onto a soda lime glass substrate by using an electron beam (e-beam) evaporation technique at a substrate temperature of 300 °C. Samples were annealed in an open atmosphere at a temperature range of 200–450 °C for 2 h. The deposited films were characterized for structural, optical, and electrical properties. Structural properties of PbS have been studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The results of XRD showed that the PbS thin film was crystalline in nature at room temperature with cubic crystal structure (galena) and preferential (111) and orientation (022). The morphology of the thin films was studied by FESEM, which also showed uniform and continuous deposition without any peel-off and patches. EDS analysis was performed to confirm the presence of lead and sulfur in as-deposited and annealed films. The thickness of the PbS film was found to be 172 nm, which is slightly greater than the intended thickness of 150 nm, determined by RBS. Ultraviolet-Visible-Near-Infrared (UV-Vis-NIR) spectroscopy revealed the maximum transmittance of ~25% for as-deposited films, with an increase of 74% in annealed films. The band gap of PbS was found in the range of 2.12–2.78 eV for as-deposited and annealed films. Hall measurement confirmed the carriers are p-type in nature. Carrier concentration, mobility of the carriers, conductivity, and sheet resistance are directly determined by Hall-effect measurement. The as-deposited sample showed a conductivity of 5.45 × 10−4 S/m, which gradually reduced to 1.21 × 10−5 S/m due to the composite nature of films (lead sulfide along with lead oxide). Furthermore, the present work also reflects the control of properties by controlling the amount of PbO present in the PbS films which are suitable for various applications (such as IR sensors).

Electronic characteristics of PbS quantum dots passivated by halides on different surfaces

The electron properties of PbS quantum dots (QDs) with different halogens passivation on different surfaces were studied by first principle calculation. The relaxation analysis showed that the vertical direction of the surface is the main relaxation direction for the PbS QDs surface. Energy analysis shows that the greater the surface energy induces higher adsorption energy. The positive adsorption energy implies that all adsorption models are exothermic and thermodynamically stable. Compared with the I atom with larger atomic number, the F atom with smaller atomic number releases more heat after adsorption on the surface, which makes the reaction easier. The energy level shift results suggest that the vacuum energy level has shifted, leading to the PbS band edge shift. The investigations dealing with the partial density of states (PDOS) show that trap state energy levels could be observed in the bandgap of PbS (110). Furthermore, with the smaller atomic number and more serious the orbital localization, more energy levels are introduced into the bandgap. It can be seen from the differential charge distribution that the S-I, I-I and Pb-I covalent bonds are formed on PbS(100), PbS(110) and PbS(111) respectively.

Структура, оптические и фотоэлектрические свойства пленок сульфида свинца, легированных стронцием и барием

The morphological evolution of composition, structural characteristics (lattice constant, microdeformations, texturing), optical and photoelectric properties of PbS films obtained by chemical bath deposition in the presence of ammonium iodide and strontium/barium chlorides at a concentration range up to 5 mmol/l was studied. According to elemental EDX analysis, the strontium content in PbS films was 0.4−0.7 at%, whereas barium concentration was beyond the determination error interval. The size of the particles forming the PbS films ranged from ~ 200 to ~ 400 nm with monomodal particle size distribution. The introduction of NH4I and SrCl2/BaCl2 into the bath retained the cubic B1 structure of PbS films, but led to a nonmonotonic change in the lattice parameter, which was associated with the defects, namely, vacancies or interstitial ions. The introduction of strontium and barium salts had no effect on the PbS band gap, but led to a change in the intensities of the impurity absorption bands in the depth and near the bottom of the conduction band. The dependence of the volt−watt sensitivity of the PbS films upon the concentration of strontium/barium in the solution was extreme with maxima at 0.05 and 0.1 mmol/l, respectively.

Trap-Free Heterostructure of PbS Nanoplatelets on InP(001) by Chemical Epitaxy.

Semiconductor nanocrystalline heterostructures can be produced by the immersion of semiconductor substrates into an aqueous precursor solution, but this approach usually leads to a high density of interfacial traps. In this work, we study the effect of a chemical passivation of the substrate prior to the nanocrystalline growth. PbS nanoplatelets grown on sulfur-treated InP (001) surfaces at temperatures as low as 95 °C exhibit abrupt crystalline interfaces that allow a direct and reproducible electron transfer to the InP substrate through the nanometer-thick nanoplatelets with scanning tunnelling spectroscopy. It is in sharp contrast with the less defined interface and the hysteresis of the current-voltage characteristics found without the passivation step. Based on a tunnelling effect occurring at energies below the bandgap of PbS, we show the formation of a type II, trap-free, epitaxial heterointerface, with a quality comparable to that grown on a nonreactive InP (110) substrate by molecular beam epitaxy. Our scheme offers an attractive alternative to the fabrication of semiconductor heterostructures in the gas phase.

Band gap tailoring of chemically synthesized lead sulfide thin films by in situ Sn doping

In the present report, undoped and tin (Sn)‐doped lead sulfide thin films were synthesized via chemical bath deposition method. The effects of Sn molar concentration on the optical, structural, and morphological properties were systematically studied. The concentration of Sn in the chemical bath was characterized by the ratio of [Sn+2]/[Pb+2] and varied from 0 to 15 at.%. Both doped and undoped thin films were polycrystalline in nature with a face‐centered cubic crystal structure; however, the preferred orientations of the crystallites were varied along the (111) and (200) planes with Sn‐doping concentration. The X‐ray powder diffraction results also showed that peak intensities and the crystalline size were decreased with increasing Sn concentration. The lattice constant varied with Sn concentration and found in the range of 6.020 to 5.944 Å. The variation of Sn concentration in PbS:Sn thin films were confirmed by energy dispersive X‐ray analyses study. The scanning electron microscope and atomic force microscopy studies revealed that Sn doping had a critical role on the surface roughness and morphology of the PbS:Sn thin films. The optical band gap study showed that the band gap of PbS:Sn thin films were engineered from 0.676 to 1.345 eV because of incorporation of Sn+2 ions via cost‐effective chemical route. Room temperature photoluminescence spectra showed a well‐defined peak at 427 nm and shoulders at 405 and 462 nm for all Sn‐doped and undoped PbS samples.

Two-electron exchange between impurity centers of tin in PbS z Se1–z solid solutions

Using emission Mossbauer spectroscopy on 119mmSn(119mSn) and 119Sb(119mSn) isotopes, the electron exchange process between neutral and doubly ionized U – tin centers is studied in partially compensated PbS z Se1–z solid solutions. The activation energy of this process for compositions with z ≈ 1 is comparable to the deposition depth of the tin energy levels in the band gap of PbS (~0.11(1) eV, and for compositions with z ≈ 1, it is comparable with the correlation energy of donor U – tin centers in PbSe (~0.05(1) eV). For all compositions of solid solutions, the exchange is realized by the simultaneous transfer of two electrons with the use of the delocalized states of the valence band.

Two-electron exchange between neutral and ionized negative-U tin centers in lead chalcogenides

Two-electron exchange between neutral and doubly ionized negative-U tin centers in PbS and PbSe has been studied by Mossbauer emission spectroscopy. The activation energy for this process in PbS is 0.11(2) eV, which is comparable to the depth of tin levels in the band gap of PbS, whereas the activation energy for this process in PbSe, 0.05(1) eV, is comparable to the correlation energy of negative-U donor tin centers in PbSe. The exchange occurs through simultaneous transfer of two electrons and involves valence band states.

The two-electron exchange between the U – tin centers in crystal and glass-like chalcogenide semiconductors

The two-electron exchange between neutral and doubly ionized U – tin centers in the partially compensated Pb0.96Sn0.02Na0.01Tl0.01S hole solid solutions in the temperature range of 80–900 K and in the partially compensated Pb0.965Sn0.015Na0.01Tl0.01Se hole solid solutions in the temperature range of 80–600 K was studied by 119mm Sn(119m Sn) Mossbauer spectroscopy. The activation energy of this process for the Pb0.96Sn0.02Na0.01Tl0.01S solid solutions is comparable with the depth of the tin energy levels in the PbS band gap and amounts to 0.11(2) eV, while in the Pb0.965Sn0.015Na0.01Tl0.01Se solid solutions it is comparable with the correlation energy of the donor U – tin centers in PbSe and amounts to 0.05(1) eV. It is established that the exchange is implemented by the simultaneous transfer of two electrons with the valence band states involved. In the glass-like (As2Se3)0.3(GeSe)0.6(SnSe)0.1 alloy containing quadruply charged six-coordinated tin (singly ionized donor center) and doubly charged three-coordinated tin (singly ionized acceptor center), no traces of the electronic exchange between differently charged tin states was observed up to a temperature of 480 K, which is explained by the fact that the doubly charged and quadruply charged tin centers are in different coordination states.

Electron exchange between impurity centers of tin in lead chalcogenides

Electron exchange between neutral and doubly ionized U-minus centers of tin in partially compensated solid solutions Pb0.96Sn0.02Na0.01Tl0.01S, Pb0.99Sn0.005Na0.005S, Pb0.965Sn0.015Na0.01Tl0.01Se, and Pb0.988Sn0.005Na0.007Se has been investigated using 119mmSn(119mSn) emission Mossbauer spectroscopy. The activation energy of the process for PbS-based solid solutions is 0.11(2) eV and is comparable to the depth of energy levels of tin in the PbS band gap, while the activation energy of this process for PbSe-based solid solutions is comparable to the activation energy of donor U-minus centers of tin in PbSe being 0.05(1) eV. The exchange has been performed by the simultaneous transfer of two electrons with the use of the valence band states.

Fabrication and Properties of Poly(vinylidenefluoride)/PbS/Au Heterogeneous Nanostructures

We report on the fabrication of polyvinylidenefluoride (PVdF) PVdF/PbS and PVdF/PbS/Au heterogeneous nanostructures by the processes, electrospinning and chemical treatment. Initially electrospinning a solution consisting of PVdF and lead acetate was used to form PVdF nanofibers loaded with Pb ions. Exposure of Pb ions loaded PVdF fibers to H2S resulted in PVdF/PbS nanostructures. The deposition of gold nanoparticles onto PVdF/PbS nanostructures results in PVdF/PbS/Au heterogeneous structure. The existence of PbS particles with an average diameter of 11 nm is evident from field emission transmission electron microscopy (FETEM) image of PVdF/PbS. The results from X-ray diffraction of PVdF/PbS also predict the size of PbS particles as in accordance with FETEM. A blue shift in the optical transition of PbS is noticed in the UV-visible spectrum of PVdF/PbS as a result of quantum confinement effect. The band gap of PbS is influenced by the presence of Au nanoparticles over the PbS particles. An equal atomic weight % of Au and PbS is found in the PVdF/PbS/Au nanostructure as inferred from energy dispersive X-ray spectroscopy (EDX). Photoluminescence (PL) spectra of PVdF/PbS and PVdF/PbS/Au are compared. Emission peaks are noticed at 400 nm and 480 nm for PVdF/PbS and PVdF/PbS/Au nanostructures respectively for an excitation wavelength of 254 nm. The presence of Au nanoclusters in PVdF/PbS/Au diminishes the intensity of photo emission of PbS.

Photoelectrical properties of In(OH)xSy/PbS(O) structures deposited by SILAR on TiO2

Photoelectrical properties of uncoated In(OH)xSy and PbS(O) layers deposited by SILAR (successive ion layer adsorption reaction) and of TiO2/In(OH)xSy/PbS(O)/PEDOT:PSS solar cell structures were investigated by spectral surface photovoltage, Kelvin-probe, current–voltage and quantum efficiency analysis. By changing the annealing temperature of In(OH)xSy in air between 50 and 350 °C, the band gap of In(OH)xSy was tuned between 2.6 and 2 eV while the band gap of PbS(O) remained unchanged at about 0.7 eV. The open circuit voltage of the solar cell structures correlated well with the band gap and the workfunction of the In(OH)xSy. Surprisingly, excess charge carriers generated in the PbS(O) layer do not contribute significantly to the short circuit current. A short circuit current of more than 10 mA cm−2 was reached by modifying TiO2 with Nb. Possible ways of optimization are discussed.

Effective mass approximation for two extreme semiconductors: Band gap of PbS and CuBr nanoparticles

An effective mass approximation (EMA) with finite-depth square-well potential is used to investigate the size-dependent band gap (BG) of PbS and CuBr nanoparticles embedded in different matrices. These two materials are interesting from the theoretical point of view as PbS is a low-BG material with smaller effective masses and larger dielectric constants, whereas CuBr is a wide-BG material with larger effective masses and smaller dielectric constants. Comparing the experimental BGs with our theoretical calculations, it is shown that EMA provides a better description of the experimental data, especially for CuBr, when the Coulomb interaction having the size-dependent dielectric constant is included in the calculation. Further, comparing the change in the BG of spherical nanoparticle, nanowire and thin film, it is predicted that the effective dimensionality of semiconductor nanoparticles can be increased by embedding them in another semiconducting matrix.