PbSe Thin Films Research Articles

Unraveling the structural and electronic properties of strained PbSe on GaAs

Thin films of PbSe have been synthesized by molecular beam epitaxy on both GaAs(100) and GaAs(111)B substrates. Despite the smaller lattice constant of GaAs, the PbSe layers are (001)-oriented and undergo in-plane tensile strain on both substrates due to the thermal expansion coefficient mismatch between the materials. High resolution transmission electron microscopy observations reveal an abrupt and highly crystalline interface, not impacted by the tensile strain. The impact of strain on the electronic band structure is computed and found to induce an increase in the energy gap by as much as 10%.

Potential photovoltaic properties of thin film solar cells based on chemically deposited ZnO/PbSe junctions

We report for the first time the fabrication of thin film solar cells based only on aqueous-phase chemically deposited ZnO/PbSe junctions. In particular, ZnO and PbSe thin films were synthesized by Successive Ionic Layer Absorption-Reaction and Chemical Bath Deposition methods. The photovoltaic performance was tested by fabricating ITO/ZnO/PbSe/Ag arrangements. Fill factors (FF), open-circuit voltages (Voc) and short-circuit current densities (Jsc) in the range of 25.4–29.2%, 0.39–0.51 V and 17.9–21.5 mA/cm2 were achieved. Power conversion efficiencies varied typically between 1.9% and 3.0%. Results showed the important photovoltaic activity of our solar cells, achieving good and comparable efficiencies to those reported by similar research. Our research represents a considerable improvement of the cost-performance relation for this kind of device.

Chemical bath deposition of high structural and morphological quality PbSe thin films with potential optoelectronic properties for infrared detection applications

Lead selenide (PbSe) thin films deposited by aqueous-based chemical methods have recently reached considerable importance for the production of different low cost and good quality optoelectronic devices. Applications in infrared devices as well as in low cost photovoltaic technologies as efficient absorbent layers have been extensively studied. In this work, the synthesis of homogeneous, polycrystalline, low-roughness, electrically conductive and narrow band gap PbSe thin films by using Chemical Bath Deposition (CBD) on glass substrates is reported. The effects of using different NaOH concentrations on the films physical and chemical properties were studied. Structural analysis realized by X-Ray Diffraction (XRD) technique showed the polycrystalline nature of the films, particularly observing a preferred <100> texture. Atomic Force Microscopy (AFM) studies revealed a compact and homogeneous growth of the thin films. A well-defined microstructure and low roughness (varying between 5 and 35 [nm]) were generally observed. Scanning Electron Microscopy (SEM) imaging studies showed the good growth quality of the thin films, observing well-defined film-to-substrate interfaces. Film thickness values between 138 ± 9 and 277 ± 20 [nm] were estimated. Chemical composition analysis realized by Energy Dispersive X-Ray Spectroscopy (EDS) exposed the non-stoichiometric nature of the PbSe films. An atomic concentration predominance of Se with respect to Pb in all samples was observed, suggesting a possible p-type conductivity. Infrared spectrophotometry measurements indicated energy band gaps in the Mid-Infrared Range (MIR), estimating values from 0.326 up to 0.393 [eV]. The thin films generally presented high electrical conductivities with respect to the typical ranges for semiconductors, estimating values in the order of 101 [(Ω·cm)−1]. Results show that the low cost and simple synthesis CBD based procedures can be used to produce high structural and morphological quality PbSe thin films with attractive optoelectronic properties (narrow band gap and electrically conductive) for the potential development of devices in infrared detection industry.

Rutherford backscattering spectroscopy analysis of the growth quality of chemical bath deposited PbSe thin films

This research focuses on the study of the growth quality, by means of the chemical profile analysis, of good structural and morphological quality chemical bath deposited PbSe thin films on glass substrates (SiO2) by Rutherford Backscattering Spectroscopy (RBS). RBS results with other complementary techniques like XRD and SEM were contrasted. Thin films by using different NaOH concentrations during the growth process were synthesized. XRD studies showed the films polycrystalline nature and their good structural quality. Pure structural effects of amorphous SiO2 and PbSe face-cubic-centered structure were observed. SEM imaging analysis revealed the good morphological growth quality of the PbSe films, observing well-defined films dimensions (thickness), a clear film-to-substrate transition at the interface and good microstructural homogeneity. According to XRD and SEM results, RBS experiments contrasted with theoretical simulations evidenced the good growth quality of the PbSe films. A good agreement between experimental data and theoretical modelling by assuming a simple film/substrate structure with a perfectly defined interface and negligible film roughness for the PbSe/SiO2 samples was achieved. RBS experimental-theoretical analysis reveal the non-stoichiometric nature of the PbSe films, being consequent with preliminary EDS based chemical studies. In particular, a predominance of Se with respect to Pb (considering the atomic concentration) in all samples was observed, suggesting a possible p-type conductivity. By stopping power analysis, thin films thicknesses between 141 and 296 [nm] were also estimated, being comparable to those obtained from SEM imaging analysis of the samples cross-sections. General results show that some aspects (chemical profile of the structure and interfaces quality) related to the growth quality of the chemical bath deposited PbSe thin films, studied by RBS experiments, are considerably intercorrelated to those analyzed by other techniques like XRD and SEM. This suggests RBS method as a suitable technique for a complete and rigorous analysis of thin films growth quality.

Reactive ion etching of PbSe thin films in CH4/H2/Ar plasma atmosphere

In this work, we reported a reactive ion etching of PbSe thin films on silicon in CH4/H2/Ar plasma atmosphere. Various etching parameters that affect dc self-bias, the etching rate and the etching smoothness of the surface and sidewalls, including rf power, gas ratio, and process pressure, have been systematically investigated. It is found that the dc self-bias has an approximate linear relationship with rf power, but it decreases as the process pressure increases. The etching rate increases with increasing rf power and decreasing process pressure. Additionally, the etching rate increases to the maximum as CH4 percentage increases to 40%, beyond which it decreases with further increasing CH4 percentage due to formation of polymer. Furthermore, SEM results show that for all investigated samples except one etched in atmosphere with 60% CH4, the etched surfaces are smooth, and the sidewalls are vertical. The etched profile of sample etched in atmosphere with 60% CH4 is very rough, which should be attributed to formation of polymer as well.

Influence of carbon in the sp1 hybridized state on the structure of PbSe thin films

The optical reflection spectra of PbSe films and PbSe films coated with a layer of linear chain carbon were studied by IR Fourier spectroscopy in the wavelength range of 1-16 μm. In all IR spectra of the samples, two minima were observed, related to plasma fluctuations of free charge carriers and related to the PbSe and PbSeO3 phases. It was found that the PbSe film coated with a layer of linear chain carbon is less oxidized. This conclusion is confirmed by the results of x-ray structural studies of the samples. The results showed a decrease in the percentage of oxygen-containing phase PbSeO3 by 2-4 times.

Photoconductive mechanism of IR-sensitive iodized PbSe thin films via strong hole-phonon interaction and minority carrier diffusion.

Photoconductive PbSe thin films are highly important for mid-infrared imaging applications. However, the photoconductive mechanism is not well understood so far. Here we provide additional insight on the photoconductivity mechanism using transmission electron microscopy, x-ray photoelectron microscopy, and electrical characterizations. Polycrystalline PbSe thin films were deposited by a chemical bath deposition method. Potassium iodide (KI) was added during the deposition process to improve the photoresponse. Oxidation and iodization were performed to sensitize the thin films. The temperature-dependence Hall effect results show that a strong hole-phonon interaction occurs in oxidized PbSe with KI. It indicates that about half the holes are trapped by KI-induced self-trapped hole centers (Vk center), which results in increasing dark resistance. The photo Hall effect results show that the hole concentration increases significantly under light exposure in sensitized PbSe, which indicates the photogenerated electrons are compensated by trapped holes. The presence of KI in the PbSe grains was confirmed by I 3d5/2 core-level x-ray photoelectron spectra. The energy dispersive x-ray spectra obtained in the scanning transmission electron microscope show the incorporation of iodine during the iodization process on the top of PbSe grains, which can create an iodine-incorporated PbSe outer shell. The iodine-incorporated PbSe releases electrons to recombine with holes in the PbSe layer so that the resistance of sensitized PbSe is about 800 times higher than that of PbSe without the iodine-incorporated layer. In addition, oxygen found in the outer shell of PbSe can act as an electron trap. Therefore, the photoresponse of sensitized PbSe is from the difference between the high dark resistance (by KI addition and iodine incorporation) and the low resistance after IR exposure due to electron compensation (by electron traps at grain boundary and electron-hole recombination in KI hole traps).

FTIR analysis of PbSe thin films after irradiation of β-ray

PbSe semi conductors are considered to be suitable product for its phototransistor implementations for IR emission. The structural characteristics of PbSe nanostructures have been studied. Placing the produced thin films of PbSe on sufficiently washed quartz molecules by thermal evaporation technique. The structural characteristics of the FTIR recording device spectroscopy design Shimadzu have been employed to calculate the transmitted and absorbed wavelengths of PbSe thin layer placed in luminous spectrum (400–4000 nm) on quartz substrates pre and post β-ray radiation.

Laser annealing to improve PbSe thin film photosensitivity and specific detectivity

PbSe thin films were deposited on SiO2/Si wafers using chemical bath deposition for mid-wave infrared (MWIR) detection. To enhance the photosensitivity of PbSe thin films, oxidation, followed by iodization, was performed to create a PbI2/PbSe two-layer system for efficient MWIR detection in the spectral range from 3 µm to 5 µm. A near-infrared (IR) laser annealing was performed after sensitization with 1070 nm wavelength at an energy density of 1J/cm2 to selectively heat the PbSe thin films. After IR laser annealing, the change in resistance between dark condition and MWIR illumination improved significantly from 19.8% to 22.6%. In addition, the dark resistance increased by 32.5% after IR laser annealing. IR photoluminescence spectra after IR laser annealing shows an increase in the sub-peak intensities from iodine incorporation. The results indicate that more iodine is incorporated into Se sites at the outer regions of PbSe grains. Therefore, more donors (electrons) from iodine diffuse into PbSe and recombine with holes so that PbSe thin film after IR laser annealing shows much higher dark resistance. Test devices with NiCr electrodes at the bottom of PbSe were fabricated with feature sizes of 40 µm to investigate the effect of IR laser annealing on electrical properties and specific detectivity (D∗). I-V characteristics show dark resistance increased after IR laser annealing. The specific detectivity increases significantly after IR laser annealing at the applied bias of 10 V at 270 K from 0.55×1010cmHz1/2W-1 to 1.23×1010cmHz1/2W-1 due to dramatic noise reduction, which is originated from higher dark resistance.

Structural and Surface morphology of Lead Selenide (PbSe) thin films

Lead Selenide (PbSe) thin films are deposited by chemical bath deposition for 2 hours in different temperature. The precursors used are 0.2M of Lead (II) nitrate, 0.5M of Sodium Selenosulfate, 2.0M of Sodium hydroxide and 4ml of Triethanolamine. The film deposition is carried out at 50°C, 60°C, 70°C, and 80°C for 2 hours. The thickness of the film varied in the range from 1400 to 5200Å. The structural characterization of these films is carried out by X–ray diffractometar (JEOL-Japan, JDX 8030 model). The XRD pattern of PbSe films deposited at different temperature exhibit the polycrystalline structure. In the present study, Scanning Electron Microscope (JOEL 840 SEM/EDAX) is employed to analyze the surface morphology of the films. In addition, the compositions of the films are estimated from EDAX Spectrum. Therefore, it is observed that the films deposited in this work, possess strong peaks for Pb and Se and no other impurities are detected through the EDAX Spectrum, confirming high purity of the PbSe thin film.

Synthesis of a Novel Single-Source Precursor for the Production of Lead Chalcogenide Thin Films

A novel complex [Pb((SePiPr2)2N) (S2CNEt2)] has been synthesized and characterized by microelemental analysis, melting point NMR, and FT-IR spectroscopies. Its crystal structure has also been successfully determined using single-crystal X-ray crystallography. The structure indicates a distorted square pyramidal geometry with the four basal atoms being noncoplanar. The complex was used as a single-source precursor for the deposition of lead chalcogenide thin films on glass substrates at 300, 350, 400, and 450°C by AACVD. The films were characterized by SEM, EDX, and XRD. The XRD peaks matched with cubic PbSe at all temperatures. The SEM micrographs showed the formation of cubes with the lower temperatures (300–350°C) showing well-resolved cubes while with the higher temperatures (400–450°C) showing poorly resolved cubes. The EDX analyses confirmed the formation of PbSe thin films at all the deposition temperatures.

Mid-infrared photoresponse of electrodeposited PbSe thin films by laser processing and sensitization

Thin films of PbSe semiconductors are important for mid-wave infrared imaging applications. There is a need for a low-cost large-area PbSe thin film deposition process to generate highly sensitive mid-infrared (mid-IR) responsive devices. Here, we report the mid-IR response in the 3 – 5 µm wavelength for PbSe thin films prepared by the electrodeposition process followed by laser processing for densification and sensitization. Scanning electron microscope imaging shows that electrodeposited films consisted of a porous structure having an interconnected particle network. A 1064 nm wavelength pulsed laser, with 50 nanosecond pulse width, was used for homogeneous melting and fast recrystallization of the porous films to convert into planar dense thin films. A comparison of XRD patterns of the as-deposited and laser processed films revealed improvement in PbSe crystallinity with the original crystal structure remaining intact. The electrical resistivity of the laser-sintered films was found to be around 0.027 Ω-cm. The two-step sensitization process of oxidation and iodization increased the final film resistivity to 10.77 Ω-cm and was highly sensitive to mid-IR radiation. The percentage change in film resistance between dark and due to mid-IR exposure of 18.5 mW/cm2 is reported to be 15.9% at an operating voltage of 10 V. Electrodeposition of thin films followed by laser processing can emerge as a viable tool to produce the large-area uniform film for PbSe thin film applications in electronics and photonics devices.

Структура и фотоэлектрические свойства пленок PbSe, осажденных в присутствии аскорбиновой кислоты

PbSe thin films chemically deposited using ascorbic acid as an antioxidant for selenourea were examined by X -ray diffraction (XRD), scanning electron microscopy (SEM) with X -ray microanalysis (EDX) and X -ray photoelectron spectroscopy (XPS). Influence of annealing temperature on chemical and phase composition, lattice parameters, surface morphology and photoelectric properties were studied. Determined that PbSe thin films contain dopant phase PbSeO3, PbSeO4, PbI2 after annealing at 633−683K. The direct and indirect optical band gaps Eg layers were observed. It has been shown that the deposited films are comparable with known commercial samples by their threshold photoelectric characteristics and can be used to create highly sensitive IR detectors.

Оптические свойства и критические точки наноструктурированных тонких пленок PbSe

Spectroscopic ellipsometry (SE) method has been used to investigate the optical properties of nanostructured PbSe thin films obtained by chemıcal bath deposıtıon (CBD) method. For a better resolution of the structure of interband transitions and for determination of critical points, the function obtained by numerical differentiation of the experimental data of the dielectric function is used. The theoretical fitting was carried out using the "Graphical Analysis" program. The best fit ıs obtained with a 2D-critical point line shape (m = 0) for E=2÷3 eV energy region. One critical point corresponding to Eg = 2,5 eV have been determined. This value is attributed to the L4L6 transition of the Brillouin zone.

Characterization and performance of graphene–PbSe thin film heterojunction

An infrared detector with high responsivity based on graphene–PbSe thin film heterojunction was reported. High-quality PbSe thin film and graphene were prepared by molecular beam epitaxy and chemical vapor deposition, respectively. The physical characteristics of PbSe thin film and graphene were performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman measurement. The phototransistor using PbSe thin film as a sensitizer and graphene as a channel to transport excitons exhibits peak responsivity and detectivity up to ~ 420 A·W−1 and 5.9 × 1011 Jones (radiation intensity: 0.75 mW·cm−2) at room temperature in the near-infrared (NIR) region, respectively. The high optical response is attributed to the photo-excited holes transferring from PbSe film to graphene under irradiation. Moreover, it is revealed that the responsivity of graphene–PbSe phototransistor is gate-tunable which is important in photodetectors.

Гидрохимический синтез пленок халькогенидов металлов. Часть 42. Экспериментальная проверка областей осаждения PbSe селеносульфатом натрия и селеномочевиной в присутствии различных лигандов

Calculation of ionic equilibria in the reaction system for synthesis of PbSe thin films was carried out. Three reaction systems containing the following combinations of reagents were considered: sodium citrate with liquid ammonia and sodium selenosulfate (system 1) or selenourea (system 2) used as chalcogenizer, ethilendiamine, sodium acetate and selenourea (system 3).The main lead complex compoundsprevented the fast PbSe formation in system 1 and 2 in region of pH of intensive selenosulfate and selenourea decomposition were hydroxo-citrate complexes. In the system 3 complexes with ethilendiamine and acetate-ions played the most significant role. For evaluating the deposition conditions of the main and impurity phases (metal hydroxides and cyanamides) by thermodynamic calculations taking into account the sizes of critical nucleis, the boundary conditions and regions of formation of PbSe, Pb(OH)2, PbCN2 in the studied reaction systems were found. The calculation results are presented in the form of three-dimensional dependencies in the coordinates “indicator of the initial concentration of the metal salt – pH of the solution – ligand concentration” and “indicator of the initial concentration of the metal salt – pH of the solution – concentration of the chalcogenizer”. Based on the calculations and preliminary experiments, the compositions of the discussed reaction mixtures were formed for the chemical bath deposition of PbSe films, which, in addition to the main components, included a dopant in the form of ammonium iodide. In the synthesis process at a temperature of 353 K (system 1 and 2) for 60 minutes and 308 K for 90 minutes (system 3), using all the studied reaction systems on glass substrates, homogeneous PbSe layers with a thickness of ~500 to ~700 nm were obtained. The ratio between the main elements of Pb and Se in the film varies between 0.98-1.32, and the iodine content is 7-11 at.% depending on the composition of the reaction bath.

Properties of chemical bath deposited and sensitized PbSe thin films for IR detection

PbSe thin films of one-micron thickness were deposited on SiO2/Si wafers using chemical bath deposition method for IR detector applications. To sensitize the PbSe films for efficient mid-wave IR detection in the spectral range from 3 to 5 μm, oxidation at 460 °C and subsequent iodization at 350 °C were performed. The x-ray diffraction for as-grown PbSe shows poly-crystalline face-centered cubic NaCl type structure while Pb3O2(SeO3) oxide peak develops as a function of oxidation time. The existence of Se-rich structure may lead to p-type conduction. Scanning electron microscope and cross-sectional energy dispersive x-ray depth profile measurements after oxidation show the top layer of the film contains primarily Pb-Se-oxide while film at the bottom layer was PbSe. After sensitization, polytype trigonal 12R PbI2, Pb3O2I2 and PbSe were confirmed. The top layer of the sensitized PbSe film was found to be converted to primarily PbI2 while the bottom layer remained PbSe. However, during sensitization without oxidation, little PbSe remained because most of the PbSe was converted into PbI2. Also, the presence of metallic Pb nano-crystals with 10 nm diameter was detected in the sensitized film.

Hydrothermal synthesis of nanoporous lead selenide thin films: photoelectrochemical and resistive switching memory applications

The interconnected nanoporous lead selenide (PbSe) thin films were synthesized with the aid of polyvinyl alcohol (PVA) as a surface directing agent by simple hydrothermal route. Films were deposited with different time intervals like 1, 2 and 3 h. Effect of time variation was studied by structural, morphological and optical characterizations. XRD analysis revealed that the film exhibit a cubic phase of PbSe. SEM study shows an evolution in nanoflakes like morphological feature. It is observed that, the nanoflakes become denser with an increase in the diameter of the platelets as the deposition time increases. Interconnected nanoporous network, forming well defined 3D nanoenvelopes has been developed to analyze solar cell and resistive switching properties. The photoelectrochemical (PEC) performance of nanoporous PbSe thin films was tested in Polysulfide electrolyte. Among all PbSe films, the sample prepared at 3 h shows higher PEC performance with maximum short circuit current 97 µA/cm2 and open circuit voltage 110 mV. In addition to this, Ag/PbSe/FTO thin film device shows the photo-induced resistive switching behavior. The non-volatile memory results suggested that the memory device is able to switch up to 104 cycles and store the data up to 103 s with good uniformity during the resistive switching process. The analysis of I–V results revealed that the Ohmic and space-charge-limited current are responsible for current conduction in the Ag/PbSe/FTO thin film memory device. The results of present investigation suggest that the nanoporous lead selenide thin films are potential candidate for the photoelectrochemical and resistive switching memory applications.

Mid-wavelength infrared photo response and band alignment for sensitized PbSe thin films

PbSe thin films were deposited using the chemical bath deposition method and sensitized with iodine for enhanced IR photoconductivity. After sensitization, PbSe films showed a high photoresponse of 44.7% in terms of resistance change in the midinfrared wavelength range (3–5 μm). To investigate the origin of high photoresponse in sensitized PbSe films, the bandgap, work function, and valence band maximum were measured by photoluminescence (PL) and X-ray photoelectron spectroscopy secondary cutoff and valence spectra. Infrared photoluminescence spectra showed a PbSe bandgap of 0.29 eV. Visible PL spectra showed a PbI2 bandgap of 2.41 eV. Work functions of as-grown PbSe and PbI2 in sensitized PbSe were determined to be 4.30 eV and 4.50 eV, respectively. An Ag/PbSe/Ag band diagram shows a measured barrier height of 0.25 eV at the PbSe/Ag interface due to Fermi level pinning. When the Ag/PbI2/PbSe/PbI2/Ag structure is biased and exposed to midwavelength infrared illumination, the electron flow is limited due to high barriers at the interfaces. Therefore, the only hole can flow after charge separation such that the electrical resistance of PbSe film is dramatically reduced. The measured bandgap, work function, and valence band maximum along with measured barrier height for metal contacts should help in providing the understanding of the charge transport mechanism in PbSe photoconductors.

Thermal Conductivity and Phonon Scattering Processes of ALD Grown PbTe–PbSe Thermoelectric Thin Films

AbstractThis work studies the thermal conductivity and phonon scattering processes in a series of n‐type lead telluride‐lead selenide (PbTe–PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe–PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer–Weber mode of growth promotes grains with a preferred columnar orientation. The ALD growth of these lead‐rich PbTe, PbSe, and PbTe–PbSe thin films results in secondary oxide phases, along with an increase microstructural quality with increased film thickness. The compositional variation and resulting point and planar defects in the PbTe–PbSe nanostructures give rise to additional phonon scattering events that reduce the thermal conductivity below that of the corresponding ALD‐grown control PbTe and PbSe films. Temperature‐dependent thermal conductivity measurements show that the phonon scattering in these ALD‐grown PbTe–PbSe nanostructured materials, along with ALD‐grown PbTe and PbSe thin films, are driven by extrinsic defect scattering processes as opposed to phonon–phonon scattering processes intrinsic to the PbTe or PbSe phonon spectra. The implication of this work is that polycrystalline, nanostructured ALD composites of thermoelectric PbTe–PbSe films are effective in reducing the phonon thermal conductivity, and represent a pathway for further improvement of the figure of merit (ZT), enhancing their thermoelectric application potential.