PbSe Thin Films Research Articles

Annealing temperature effects on optical and photoelectric properties of sputtered indium-doped PbSe thin films

Indium-doped PbSe thin films deposited on Si(111) by magnetron sputtering were annealed at different temperatures and characterized using the X-ray diffraction, Fourier transform infrared spectroscopy and physical properties measurement system. After the annealing treatment, an oxidation layer containing PbSe, PbO, SeO2 and In2Se3 is formed on the film surface. The optical band gap of the annealed samples increases to a maximum of 0.276 eV at 150 °C, and then decreases with the annealing temperature due to the position shift of the valence band maximum and the conduction band minimum. The photoelectric sensitivity of the annealed indium-doped PbSe thin films increases by 1.5–2 times, compared with the untreated samples. Moreover, the average value of the resistance change rate increases almost linearly with the annealing temperature due to the concentration of the dark charge carriers increases with the annealing temperature confirmed by the Hall effect measurements.

Structure and composition effects on electrical and optical properties of sputtered PbSe thin films

Lead selenide (PbSe) thin films were grown on Si (111) substrates using magnetron sputtering, and the structure and composition effects on the photoelectric and optical properties of the sputtered PbSe thin films were studied using field emission scanning electron microscope, energy dispersive X-ray detector, X-ray diffraction, X-ray photoelectron spectroscopy, physical property measurement system and Fourier transform infrared spectroscopy. The optical band gaps of all the sputtered PbSe thin films ranged from 0.264eV to 0.278eV. The PbSe thin film prepared with oxygen flux 1.0sccm, deposition time 240min, sputtering power 150W and substrate temperature 150°C showed the highest resistance change rate under illumination, about 84.47%. The variation trends of the photoelectric and optical properties with the average crystal size, lattice constant, oxygen content and lattice oxygen percentage were similar, respectively. The sputtered PbSe thin films showed poor photoelectric sensitivity, when the average crystal size was similar to the Bohr radius (46nm), while the photoelectric sensitivity increased almost linearly with the oxygen content in the thin films, indicating that both deviating the average crystal size from the Bohr radius and increasing the oxygen content are two direct and effective ways to obtain high photoelectric sensitivity in PbSe thin films.

Study on the growth mechanism and optical properties of sputtered lead selenide thin films

Lead selenide thin films with different microstructure were deposited on Si (100) substrates using magnetron sputtering at 50°C, 150°C and 250°C, respectively. The crystal structure of the sputtered PbSe thin films varies from amorphous crystalline to columnar grain, and then to double-layer (nano-crystalline layer and columnar grain layer) structure as the deposition temperature increases, which is due to the dominating growth mode of the thin films changes from Frank–van der Merwe (or layer-by-layer) growth mode at 50°C to Volmer–Weber (or 3D island) growth mode at 150°C, and then to Stranski–Krastanow (or 3D island-on-wetting-layer) growth mode at 250°C. The growth mechanism of the sputtered PbSe thin films is mainly dominated by the surface and strain energy contributions. Moreover, the strain energy contribution is more prominent when the deposition temperature is less than 180°C, while, the surface energy contribution is more prominent when the deposition temperature is higher than 180°C. The absorption spectra of the sputtered PbSe thin films are in 3.1–5μm range. Besides, the sputtered PbSe thin film prepared at 250°C has two different optical band gaps due to its unique double-layer structure. According to the theoretical calculation results, the variation of the band gap with the deposition temperature is determined by the shift of the valence band maximum with the lattice constant.

Effect of bath temperature on PbSe thin films prepared by chemical synthesis

Lead selenide (PbSe) thin films were deposited using chemical bath deposition techniques by varying bath temperatures (70–90°C) keeping deposition time and other parameters constant. The influence of the synthesis/bath temperature on structural and thermoelectric properties of as-deposited PbSe nanostructured film was investigated using x-ray diffraction, scanning electron microscope, Raman spectroscopy and thermo-emf measurement. The improvement of crystallinity of the PbSe films was studied using x-ray diffraction and Raman scattering. The structural parameters, such as the lattice constant (a), crystallite size (D), dislocation density (δ) and microstrain (ε) were evaluated from XRD spectra. The average crystallite size, as calculated from Scherrer's formula, increased from 22.45 to 24.87nm as the bath temperatures was varied from 70°C to 90°C. The dislocation density and microstrain were found to vary inversely with the crystallite size, whereas the lattice constant was found to slightly different with an increase in crystallite size. The scanning electron microscopy observation shows that with an increase in bath temperature, the grain size increases and they agglomerates. At the elevated bath temperatures individual particles agglomerate and lead to higher grain density and film crystallinity. The thermo-emf measurements have shown n-type conductivity in the as deposited films.

Effect of hydrazine hydrate concentration on structural, surface morphological and optoelectronic properties of SILAR deposited PbSe thin films

Lead Selenide (PbSe) thin films have been deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method to investigate the effect of hydrazine hydrate on film properties. The peak behavior of the X-ray diffractogram corroborates crystalline nature of PbSe thin films. The intensity of the major peaks attributable to PbSe improved at higher concentrations up to 5ml HH and gets reduced for 7ml HH. The average crystallite size is in the range 18.18–33.37nm. The film surface of lower HH sample is composed of spherical grains which are arranged in a compact manner. On increasing HH some clusters appears on the surface of the film over a homogeneous background. The AFM micrographs show that the surfaces of the lead selenide thin films consist of dense distribution of nanoscale particles with a range of grain sizes. The roughness obtained is in the range 13.7–76.3nm. Highly crystalline sample, 5HH exhibits very good topography. The direct band gap values are in the range 1.425–1.803eV. Thus by varying HH we have been able to tune the band gaps over a wide range. The highly crystalline sample 5HH with least strain and excellent topography exhibits maximum conductivity.

Influence of substrate temperature on structural, morphological and electrical properties of PbSe film deposited by radio frequency sputtering

PbSe films were prepared by radio frequency magnetron sputtering from PbSe slices target under different substrate temperatures (from room temperature to 300°C). The effect of substrate temperature on structural properties of PbSe thin film was investigated. The surface morphology and the crystal structure of film were determined using field emission scanning electron microscopy and X-ray diffractometry, respectively. It was found that the grain shape changed with substrate temperature. When the substrate temperature was below 250°C, most of the crystal grains were spherical in shape. For temperatures above 250°C, the grains transformed to triangle or prismatic ones. Meanwhile, with increasing substrate temperature, the preferential orientation of the film changed from (200) to (220). To figure out the intrinsic mechanisms for this behavior, the texture coefficient, as well as the comparison between surface energy and elastic strain energy was performed. At lower temperature, the film growth was determined by surface energy, which was replaced by strain energy at higher temperature. Therefore, the diversity of crystal structure and morphology of the films at different substrate temperatures occurred. Moreover, the electrical properties of the p-type PbSe films are also quite dependent on substrate temperature. With substrate temperature increased, the electrical resistivity decreased from 1.88 to 0.14Ωcm, while the carrier concentration increased from 1.74×1018 to 4.08×1019cm−3 as the mobility was enhanced from 0.54 to 2.21cm2/Vs.

Impact of thickness on crystal structure and optical properties for thermally evaporated PbSe thin films

Nanocrystalline lead selenide (PbSe) thin films with varied thickness were deposited on glass substrates by thermal evaporation technique. Physical and surface properties of PbSe films were examined by XRD, AFM, UV–Vis spectra. It was found that the structural and optical properties of the PbSe films were strongly dependent on thickness. On one hand, the particles were uniformly distributed in the surface for the thinner samples. On the other hand, however, the particles began to aggregate and worm-like structures appeared for the thicker ones (93 nm and 127 nm). The absorption band-edge was red shifted with increasing thickness. The optical band gap ranging 2.04–2.30 eV with thickness was observed. This could be attributed to the increasing of grain size and the improvement of film uniformity.

Thickness effect on the band gap of magnetron sputtered Pb45Se45O10 thin films on Si

Oxygen doped PbSe thin films with different thickness were grown on the Si (100) substrates by magnetron sputtering, and characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and physical properties measurement system. As the film thickness increased, the intensity of the (200) PbSe prominent diffraction peak increased, while the (220) peak almost vanished, indicating the primary growth direction. The change rate between the light and dark resistance increased with the film thickness, and the maximum of 64.76% was obtained. According to the density functional theory calculations and the experimental results, the band gap of the PbSe thin films decreased from 0.278eV to 0.21eV when doped with oxygen. Doping with oxygen during the deposition process is a viable way to prepare PbSe thin films with a tunable band gap. The band gap increased almost linearly with the lattice constant, confirmed by the calculated and experimental results.

Hot carrier solar cell with semi infinite energy filtering

Energy filtering of hot carriers in a solar cell may be attained by using band offsets at heterointerfaces. This rough energy filtering does not require special sophisticated energy filtering contacts, and may be implemented in the form of a double heterojunction. PbSe thin film as absorber layer was electrodeposited on InP single crystal. Experimental evidence of hot carrier filtering at InP/PbSe heterointerface at room temperature was obtained by double beam optoelectrical measurements. The measurements can be interpreted by thermionic emission over the band offset barriers. The valence band offset of 0.3eV at the InP/PbSe heterointerface was measured by X-ray Photoelectron Spectroscopy. The filtering process may become useful for new generation of hot carrier solar cells.

Observation of the Meyer–Neldel rule in nanocrystalline PbSe thin films

In this paper, nanocrystalline lead selenide (nc-PbSe) thin films have been chemically deposited on glass substrates using appropriate chemical reagents in aqueous alkaline media. The structural, morphological, optical and electrical properties of PbSe thin films have been studied. X-ray diffraction (XRD) analysis indicates that these films have a cubic structure with an average grain size of ∼21 nm. The field emission scanning microscope (FE-SEM) micrograph shows that the films have a dense surface with a smooth granular structure and well-defined grain boundaries. The σ(T) measurements were carried out under vacuum over a wide temperature range (77–350 K) for nc-PbSe films with a thickness of 375 ± 10 nm. The temperature dependence of dark dc conductivity σ(T) in PbSe nanocrystalline (nc) thin films is found to obey the Meyer–Neldel rule (MNR). The MNR correlates the spread in the thermal activation energy of conduction (ΔE) with the exponential pre-factor (σ0) of the Arrhenius conductivity formula.

Dialkyldiselenophosphinato-metal complexes – a new class of single source precursors for deposition of metal selenide thin films and nanoparticles

We report here a new synthetic approach for convenient and high yield synthesis of dialkyldiselenophosphinato-metal complexes. A number of diphenyldiselenophosphinato-metal as well as diisopropyldiselenophosphinato-metal complexes have been synthesized and used as precursors for deposition of semiconductor thin films and nanoparticles. Cubic Cu2-xSe and tetragonal CuInSe2 thin films have been deposited by AACVD at 400, 450 and 500 °C whereas cubic PbSe and tetragonal CZTSe thin films have been deposited through doctor blade method followed by annealing. SEM investigations revealed significant differences in morphology of the films deposited at different temperatures. Preparation of Cu2-xSe and In2Se3 nanoparticles using diisopropyldiselenophosphinato-metal precursors has been carried out by colloidal method in HDA/TOP system. Cu2-xSe nanoparticles (grown at 250 °C) and In2Se3 nanoparticles (grown at 270 °C) have a mean diameter of 5.0 ± 1.2 nm and 13 ± 2.5 nm, respectively.

ALD Synthesis of PbSe Thin Films inside Porous Si Templates for Innovative Thermoelectric Applications

The IV-VI lead chalcogenides are considered as prospective thermoelectric materials which have their potential applications in green renewable energy by waste heat recovery and infrared devices. Among these materials, PbSe demonstrates a remarkable thermoelectric performance, The thermoelectric figure of merit ZT exceeds 1 for both n-type and p-type PbSe at high temperature. ZT is defined as ZT=σS2T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity, respectively. In addition, Se element is more abandant and less costly than Te which is a scarce element [1].PbSe thin films on Si substrates have been synthesized by various methods. However, a careful literature search reveals, there are few if any reports on the synthesis of PbSe thin films by atomic layer deposition (ALD). The ALD technique exhibits self-limiting surface reactions in each ALD cycle which consequently results in precise layer thickness control, stoichiometry, composition, uniformity of large area on the substrate. ALD also can be used to deposit conformal film onto very complex substrates or nano-porous template surfaces. This is the one advantageous property of ALD which renders it more competitive and promising in porous template nano-structures. In contrast, magnetron sputtering and PLD cannot be used to coat complex 3D structures with PbSe. Furthermore, the growth temperature of ALD is rather low in comparison with other fabrication processes.In this work we report on the successful synthesis of multiple PbSe thin films on silicon substrates and inside microporous Si templates by thermal ALD, using lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2) and (trimethylsilyl) selenide ((Me3Si)2Se) as the chemical ALD precursors for lead and selenide, respectively. The repetitive structure of nano-porous Si templates offers an additional degree of periodicity in the quest for high ZT thermoelectric films.The XRD and FE-SEM results reveal that the Lead selenide thin films are polycrystalline at deposition temperatures of 170 °C based on Volmer Weber Island growth mode and have characteristic FCC rock-salt crystal structure as shown in Figure (1), (2) and (3).

AC Conduction and Dielectric Characterization of Vacuum Evaporated PbSe thin Films

Thin films of PbSe are prepared by vacuum deposition technique on to well cleaned glass substrates. Thin film capacitors of the type (Al-PbSe-Al) have been fabricated. AC Conduction and Dielectric studies performed on samples of thickness 300,500 and 700nm at various frequencies (10kHz-10MHz) and temperatures (293K-493K).From the AC conduction studies, it is confirmed that the mechanism responsible for the conduction process is hopping. Thermal activation energy is found to decrease with increase in film thickness. The variations of the dielectric constant and loss as function of frequency at different thicknesses and temperatures are observed and the results are discussed. The polarizability α is found to decrease with the increase of thickness while it increases with temperature.

Structural and optical properties of ZnSe thin films stacked with PbSe submonolayers

Structural and optical properties of Zinc Selenide (ZnSe) thin films stacked with multiple Lead Selenide (PbSe) submonolayers (ML) were studied. Thermal evaporation was preferred to produce ZnSe–PbSe thin films with the PbSe ML thickness ranges from 2.5 to 10 nm. Polycrystalline nature of the ZnSe was revealed through high resolution X-ray diffractometer measurement. The development of micro strain at the interfaces with increasing PbSe ML thickness was observed. A cross-sectional TEM image shows well-ordered periodicity and reproducibility of the layer thickness. The enhancement of optical absorption of ZnSe was identified upon stacking of PbSe ML. The evidence for quantum confinement in PbSe ML was revealed by the obtained red shift in band gap (2.5–1.8 eV) values as well as photoluminescence emission at 1,071 nm. The presence of tensile strain in the ZnSe layers upon staking of PbSe ML was discussed by the shift in LO phonon modes in Raman spectra.

Band gap engineering in PbSe thin films from near-infrared to visible region by photochemical deposition method

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32–1.40 eV for films deposited on soda lime glass substrates and 1.46–1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10−7–513 × 10−7 (Ω cm)−1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate.

Growth and opto-electro-structural properties of nanocrystalline PbSe thin films

The present work deals with the structural, optical and electrical characterization of PbSe thin films with variable thickness deposited on well-cleaned glass substrates by electron beam evaporation technique at room temperature (RT). Grown films are characterized by X-ray diffraction, energy dispersive spectroscopy, resistivity measurements (from room temperature to 200°C) and optical measurements at room temperature in order to study their various properties. The optical constants (namely, absorption coefficient, the refractive index, extinction coefficient, real and imaginary part of dielectric constant) have been studied for as-deposited PbSe thin films as a function of photon energy in the wavelength range 400–2500nm at RT. The thickness dependence of optical constants was discussed.

Chemically deposited PbSe thin films: factors deterring reproducibility in the early stages of growth

The early stages of growth in chemical solution deposition of lead selenide thin films on GaAs(100) substrates were studied in detail.

Atomic Layer Deposition of Nanolaminate Structures of Alternating PbTe and PbSe Thermoelectric Films

For this study PbTe and PbSe thin film nanolaminates have been prepared on silicon substrates with native oxide by Atomic Layer Deposition (ALD) using lead(II)bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and bis-(triethyl silyl) selane ((Et3Si)2Se) as ALD precursors for lead, tellurium and selenium. The experimental evidence revealed the ALD growth of lead telluride and lead selenide followed the Vollmer-Weber island growth mode. We found a strong dependence of the nucleation process on the temperature. In this paper, we present the optimized conditions for growing PbTe and PbSe thin film nanolaminates within the ALD process window range of 170°C to 210°C and discuss an early nano-scale PbTe/PbSe bilayer structure. Results of various physical characterizations techniques and analysis are reported.

ALD Growth of PbTe and PbSe Superlattices for Thermoelectric Applications

For this study PbTe and PbSe thin films have been prepared on silicon substrates with native oxide by Atomic Layer Deposition (ALD) using lead (II)bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and bis-(triethyl silyl) selane ((Et3Si)2Se) as ALD precursors for lead, tellurium and selenium . Instead of classic layer by layer ALD growth the initial ALD nucleation of lead telluride was found to follow the Vollmer-Weber island growth model. We found a strong dependence of the nucleation process on the temperature. In this project, we present the optimized conditions for growing PbTe and PbSe thin films within the ALD process window range of 170 °C to 210 °C and discuss early nanolaminate structures. Results of various physical characterizations techniques and analysis are reported.

Antimony Chalcogenide/Lead Selenide Thin Film Solar Cell with 2.5% Conversion Efficiency Prepared by Chemical Deposition

Antimony sulfide-selenide solid solutions offer optical band gaps, Eg, in the 1–1.88 eV interval; and lead selenide offers Eg upward of its bulk value, 0.28 eV, depending on the extent of quantum confinement. In this work, thin film solar cells of SnO2:F/CdS/Sb2(Se/S)3/PbSe/C-Ag are developed by chemical deposition of the thin films on transparent conductive oxide (TCO) glass. To prepare the solar cell, first a CdS thin film of 100 nm in thickness is deposited on the TCO from a solution containing Cd(II)-citrate complex. On this, a thin film is deposited from a solution containing potassium-antimony tartrate, thioacetamide and selenosulfate, which upon heating at 280°C in nitrogen ambient results in a Sb2S1.2Se1.8 film of 150 nm in thickness with an Eg of 1.67 eV. PbSe thin film 110 nm in thickness is deposited on it from a solution of Pb-citrate complex and selenosulfate, with crystalline grain diameter 10 nm, and Eg of 1.86 eV. The cell shows open circuit voltage (Voc), 454 mV, short circuit current density (Jsc) 12.5 mA/cm2, fill factor (FF) 0.44 and conversion efficiency (η) 2.5%. The observed cell parameters are backed by a tentative energy level diagram and an estimate for the light generated current density.