PbSe Thin Films Research Articles

Enhancing the Detection Sensitivity of PbSe Thin Film TTE Photodetector by Adding Light-Trapping Coatings

Enhancing the Detection Sensitivity of PbSe Thin Film TTE Photodetector by Adding Light-Trapping Coatings

Enhanced Response of Si-Based PbSe Thin Film MSM Photodetectors by Photon-Trapping Hole Array in the Surface

Enhanced Response of Si-Based PbSe Thin Film MSM Photodetectors by Photon-Trapping Hole Array in the Surface

One-pot synthesis, sensitization and photoelectric performance of calcium doped PbSe thin films

One-pot synthesis, sensitization and photoelectric performance of calcium doped PbSe thin films

Comparative Assessment of Optical and Solid-State Characteristics in Antimony-Doped Chalcogenide Thin Films of ZnSe and PbSe to Boost Photovoltaic Performance in Solar Cells

Solar cell efficiency is crucial for maximizing the potential of solar energy as a sustainable power source. This research investigates the optical and solid-state properties of antimony-doped ZnSe and PbSe thin films using the spray pyrolysis technique. The process involves meticulous cleaning of soda-lime glass substrates, deposition of precursors (antimony chloride (SbCl3), lead chloride (PbCl2), hydrated zinc acetate (Zn (CH3COO) •3H2O), and sodium selenosulfide (NaSeSO3) via nebulizer-driven atomization onto heated substrates at a temperature of 80°C, and subsequent annealing at 300°C in a controlled nitrogen atmosphere for 60 minutes, facilitated by a tube furnace. Optical property evaluation through UV-Vis spectrophotometry reveals intriguing trends, such as a decrease in absorbance and an ascending transmittance with elongated wavelengths. Annealed films exhibit peak optical conductivity values around the visible spectrum, and augmented refractive indices correlate with increased wavelengths, further enhanced through annealing. Antimony doping influences band gap energy, making these materials promising for solar cell fabrication. This study underscores the potential of antimony-doped ZnSe and PbSe thin films to enhance solar cell efficiency. The films offer features like enhanced light trapping, lowered band gap energy, and improved charge transport characteristics, making them suitable for various solar cell applications, including antireflection coatings and light-trapping layers. Continued exploration and refinement of these materials are anticipated to lead to novel advancements in solar cell design and manufacturing, contributing to more efficient and impactful energy conversion techniques.

Effect of Holding Time on Structure and Optical Properties of PbSe Films Deposited in a Chemical Bath on Si(100) Substrates

Lead selenide (PbSe) thin films are widely used in the field of infrared detection due to their high infrared detection rate and sensitivity at room temperature. In recent years, PbSe thin films have been successfully grown on Si substrates. This article utilized the chemical bath deposition (CBD) method to prepare uniform and dense PbSe thin films on Si(100) substrates. The crystal structure, micro morphology, thickness, and energy band gap of polycrystalline PbSe thin films on Si(100) substrates were studied at a deposition temperature of 70 °C with a holding time of 30–120 min. Results showed that the prepared PbSe films bonded well with the Si(100) substrate. As the holding time increased, PbSe maintained [200] crystal orientation growth, and the crystallinity improved. The thickness of the PbSe thin film increased with the holding time, while the energy band gap first decreased and then increased. The PbSe thin film prepared with a holding time of 60 min had a thickness of about 388.5 nm, grew in the [200] crystal orientation, and had an energy band gap of 0.153 eV, showing the best optical properties.

Fabrication and Electrical Characterization of p/n PbSe Diodes

Lead selenide (PbSe) diodes were fabricated using a magnetron sputtering process system with a pulsed DC power supply and a 2-inch PbSe target with a purity of 5N. For p-type PbSe thin films, the process variable was the oxygen ratio in the mixed gas of argon and oxygen. The electrical characteristics of the thin films were observed after heat treatment. For the n-type PbSe, nickel (Ni) was used as a doping material. The deposition and doping were performed simultaneously using a co-sputtering method. During co-sputtering, the input power of the Ni sputter gun was adjusted as a process variable. Hall measurement experiments were performed to measure the doping concentration and resistivity of both the p-type and n-type PbSe semiconducting films. The maximum doping concentration was 2.33×10<sup>19</sup> cm<sup>-3</sup> for p-type PbSe and 7.55×10<sup>20</sup> cm<sup>-3</sup> for n-type PbSe thin films, respectively. The p-n junction IV curve showed that the lowest forward voltage generation point, V<sub>f</sub>, was 1.5 V and the reverse breakdown voltage was -4.3 V. In the photocurrent measurement, the photo sensitivities of the heat-treated samples were higher than that of the non-treated sample, and the maximum value was 5.148. Photo responsivity was also higher in the heat-treated samples. Its maximum was 0.7306 mA / W.

Effect of N2/I2 atmosphere annealing sensitization on PbSe-based photodetector for NIR photodetection

Lead selenide (PbSe) detectors have garnered widespread utility in infrared detection due to their advantages of low-Russian compounding and uncooled operation. In this study, PbSe thin films were firstly deposited on glass using selenourea (SeC(NH2)2) as the selenium source by chemical bath deposition. The changes in morphology, composition, structure, and photoelectric properties of PbSe films thermally sensitized in 4 atm of O2, N2, O2/I2, and N2/I2 were investigated. It was discovered that PbI2 was supplied to the film surface following thermal sensitization in the I2 atmosphere to create a PbSe/PbI2 separation model, promoting photogenerated charge separation and enhancing PbSe optoelectronics' performance. The device's dark current is decreased to 1/136 before annealing, the on-off ratio is increased by 18.7 times, the reaction time is only a few tens of μs, and the response speed is increased by 105 times after N2/I2 thermal sensitization.

Laser fabrication of lead selenide infrared focal plane array devices

The motivation of this work is to demonstrate the versatility and potential of laser processing in the fabrication of PbSe thin films and focal plane array devices. This work fabricates an FPA device with any need for the suite of equipment and chemicals necessary for photolithography and etching. Advances in laser technologies and the vast number of laser parameters available are enabling the huge potential for laser processing of thin films and device fabrication. This can be accomplished faster using lasers with fewer steps than using conventional thin film deposition and photolithography methods. This work presents the fabrication and simple operation of a proof-of-concept PbSe-based, 120-pixel PFA (10 × 12 pixel) focal plane array using only laser processing for film deposition and device patterning. Lasers were used to both deposition and pattern a PbSe film with 60 × 70 µm pixels with 100 µm pitch with a unit cell photoresponse of 17% DelR. Additional results, challenges, limitations, and suggested future improvements are presented.

Effect of oxygen and nitrogen sensitization on structural, optical and electrical properties of PbSe thin films

An effective two-step sensitization technique was implemented in PbSe thin films, leading to a remarkable improvement in the optoelectronic performance of PbSe photodetectors. The phase composition, surface and cross-sectional morphology, temperature-dependent carrier concentration and mobility as well as the detectability of PbSe films after sensitization were systematically investigated using characteristic techniques. The optimal PbSe film oxygen sensitized at 450 °C exhibited a room-temperature photodetection with a carrier concentration of 5.31 × 1016 cm−3, carrier mobility of 16.52 cm2/V−1s−1, and detectivity of 2.25 × 109 Jones. High-temperature argon heat treatment and oxygen sensitization of PbSe films are expected to suppress recombination losses and significantly improve the optoelectronic properties of sensitized PbSe films due to enhanced carrier separation and transport. The enhanced photoresponse mechanism of the PbSe films through two-step sensitization method was also discussed. These results suggest that the proposed method can be applied to high-performance lead selenide photodetectors.

Mid-wave infrared photoluminescence from low-temperature-grown PbSe epitaxial films on GaAs after rapid thermal annealing

We investigate the beneficial effects of rapid thermal annealing on structure and photoluminescence of PbSe thin films on GaAs (001) grown below 150 °C, with a goal of low temperature integration for infrared optoelectronics. Thin films of PbSe deposited on GaAs by molecular beam epitaxy are epitaxial at these reduced growth temperatures, yet the films are highly defective with a mosaic grain structure with low angle and dendritic boundaries following coalescence. Remarkably, we find that rapid thermal annealing for as short as 180 s at temperatures between 300 and 425 °C in nitrogen ambient leads to extensive re-crystallization and transformation of these grain boundaries. The annealing at the same time dramatically improves the band edge luminescence at 3.7 μm from previously undetectable levels to nearly half as intense as our best conventionally grown PbSe films at 300 °C. We show using an analysis of laser pump-power dependent photoluminescence measurements that this dramatic improvement in the photoluminescence intensity is due to a reduction in the trap-assisted recombination. However, we find it much less correlated with improved structural parameters determined by x-ray diffraction rocking curves, thereby pointing to the importance of eliminating point defects over extended defects. Overall, the success of rapid thermal annealing in improving the luminescent properties of low growth temperature PbSe is a step toward the integration of PbSe infrared optoelectronics in low thermal budget, back end of line compatible fabrication processes.

THE EFFECT OF THERMAL OXIDATION ON THE PHOTORESPONSE PROPERTIES OF PbSe PHOTODETECTORS

In this study, thin PbSe films were deposited on the Si(100) by ion beam sputtering aiming at forming photoconductive infrared detectors. PbSe photodetectors are then gained through thermal oxidation over different temperatures for sensitization. The effect of oxygen sensitization on the morphology, composition and structure of PbSe photodetectors is studied. It was found that during the sensitization, the PbSe thin film grains gradually refine the melting junction due to oxidation and recrystallization. The proportion of the film surface O/(PbSe) atoms increased significantly, while the Se/Pb atoms greatly decreased due to the increased gasification of SeO2. The noise signal for sensitized PbSe films decreased and the detection rates were improved. The sensitization process designed in this paper helps to improve the photoresponse function of PbSe films.

High sensitivity and fast response self-powered PbSe ultraviolet pulsed photodetectors based on the transverse thermoelectric effect

Light-induced transverse thermoelectric (TTE) effect has attracted extensive attentions because of the great potential application in self-powered photodetectors. In this paper, we report the ultraviolet pulsed light-induced TTE effect in the inclined PbSe thin films. Without any external voltage applied, gigantic open-circuit voltage signals with ultrafast responses in the order of nanoseconds were obtained when the film surface was irradiated by a 308 nm pulsed laser. The voltage sensitivity Rs can reach up to ∼7.75 V/mJ and the figure of merit Fm is as high as ∼350 mV/ns, both of which are higher than the best values reported in most of complex oxide thin films. In addition, the experimental results reveal that the polarity of the induced voltage will immediately reverse when the film is irradiated from the substrate side and the amplitudes of the voltage are linearly proportional to sin2α (α is the inclination angle of the films). Here, the anisotropy of the Seebeck coefficient is used to explain the origin of the TTE voltage. The results demonstrate the great potential application of PbSe thin film for the high sensitivity and fast response self-powered ultraviolet pulsed photodetectors.

Lead Selenide Thin Films and Uncooled Midinfrared Detectors by Vapor Phase Deposition.

The broad application of lead selenide (PbSe)-based uncooled midinfrared (MIR) detectors has been hindered by the nonuniformity of wafer-level films prepared by the conventional chemical bath deposition (CBD) method. Herein, using a vapor phase deposition (VPD) approach, we demonstrate the deposition of 3 in. wafer-scale uniform PbSe thin films with thicknesses of up to 1.5 μm. To trigger the MIR response, the as-grown films were sensitized at an elevated temperature in an oxygen-iodine atmosphere. We discovered that the key to spark off the MIR response of the PbSe detector originated from the self-assembled rodlike microstructures in the thin films, which can be controlled by the I2/PbSe flux ratio in the VPD process. At room temperature, the thin film detector exhibits an excellent optoelectronic performance, with detectivity up to 2.4 × 109 cm Hz1/2 W-1 achieved under optimized conditions. Our results show that the VPD method opens up a new avenue to the industrialization of uncooled lead-salt MIR detectors.

Ultra-broadband light detection based on the light-induced transverse thermoelectric effect of epitaxial PbSe thin films with inclined structure

PbSe is a simple binary compound that has been studied extensively for use as a promising moderate-temperature thermoelectric material. In this Letter, we report the observation of the light-induced transverse thermoelectric (TTE) effect in c-axis inclined PbSe thin films that were grown epitaxially on c-axis miscut SrTiO3 single crystal substrates using the pulsed laser deposition technique. Because of the anisotropic Seebeck coefficient of these inclined PbSe thin films, high TTE voltage signals were detected when the film surfaces were irradiated using various different continuous-wave lasers with wavelengths ranging from the ultraviolet (360 nm) to the far infrared (10.6 μm). In addition, the amplitudes of the output voltage signals showed good linear dependence on both the radiation power density and the film inclination angle. The results above demonstrate the potential of PbSe for self-powered ultra-broadband light detection applications.

Promoted Mid-Infrared Photodetection of PbSe Film by Iodine Sensitization Based on Chemical Bath Deposition.

In recent years, lead selenide (PbSe) has gained considerable attention for its potential applications in optoelectronic devices. However, there are still some challenges in realizing mid-infrared detection applications with single PbSe film at room temperature. In this paper, we use a chemical bath deposition method to deposit PbSe thin films by varying deposition time. The effects of the deposition time on the structure, morphology, and optical absorption of the deposited PbSe films were investigated by x-ray diffraction, scanning electron microscopy, and infrared spectrometer. In addition, in order to activate the mid-infrared detection capability of PbSe, we explored its application in infrared photodetection by improving its crystalline quality and photoconductivity and reducing tge noise and high dark current of PbSe thin films through subsequent iodine treatment. The iodine sensitization PbSe film showed superior photoelectric properties compared to the untreated sample, which exhibited the maximum of responsiveness, which is 30.27 A/W at 808 nm, and activated its detection ability in the mid-infrared (5000 nm) by introducing PbI2, increasing the barrier height of the crystallite boundary and carrier lifetimes. This facile synthesis strategy and the sensitization treatment process provide a potential experimental scheme for the simple, rapid, low-cost, and efficient fabrication of large-area infrared PbSe devices.

Van der Waals growth of PbSe thin films on graphene and Bi2Se3

One of the major obstacles for integration of PbSe with Si-based electronics is the significant lattice mismatch between PbSe and Si. The rigid limitation on lattice-matching could be effectively loosened via the van der Waals growth strategy, in which as-grown film layer and underlying substrate are held together through the weak van der Waals interaction rather than the strong chemical bonds. Benefiting from the absence of dangling-bond at their surface, graphene and layered Bi2Se3 are two potential van der Waals materials for the relaxation of lattice mismatch between PbSe and Si. In this work, PbSe thin films were grown on surface of graphene and Bi2Se3 with the molecular beam epitaxy. A potential solution for the relaxation on lattice mismatch between PbSe and Si is thus explored.

Photoconductive PbSe thin films and the role of potassium iodide

The PbSe thin films are sensitized by oxidation and iodization process to improve the infrared photoresponse enabling higher performing photodetectors and photovoltaic devices. Iodine is widely used for PbSe sensitization, and it influences the thin film morphology and also forms a PbI2 passivation layer. Potassium Iodide (KI) has been used as an additive in chemical bath deposited films of PbSe since 1959 and continues to this day. This work aims to better understand the role of KI in PbSe films as it improves MWIR photoresponse by as much as 300% compared to samples without KI. In this research paper, we show that low levels of KI (180 mMol) densify the PbSe film, increase grain size, reduce film stress/cracking, and improve IR absorption (proportional to dose). The transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies show thermal annealed PbSe films with KI convert round equiaxed grains to highly faceted grains coated with PbI2 ranging from 3 to 10 nm, throughout the film. The dense PbSe grains encapsulated in PbI2 lead to a more uniform PbSeO3 layer following thermal oxidation. The electrical resistance versus temperature measurements shows a strong phase transition occurs at 220 °C only for samples with KI. X-ray photoelectron spectroscopy studies confirm that PbSe films with KI annealed in an argon atmosphere at 460 °C have a surface layer of PbI2, and no potassium was detected, suggesting desorption or diffusion of potassium into the PbSe grains. PbSe films with KI showed 30x higher electrical resistance (RD) under dark conditions, leading to reduced carrier concentration (lower dark current) and improved photoresponse without impacting electron mobility. In summary, we have clarified the role of KI in PbSe thin films and how it can be used to improve the infrared photoresponse.

High sensitivity and fast response infrared detector fabricated with the Bi2Se3-PbSe heterojunction

A heterojunction photodetector based on the photogating effect is fabricated by combining the novel topological insulator Bi2Se3 with the traditional narrow-gap PbSe. The Bi2Se3-PbSe heterojunction is constructed by depositing PbSe thin film on surface of Bi2Se3 with the molecular beam epitaxy technique. Large lattice mismatch between cubic PbSe and rhombohedral Bi2Se3 is relaxed through the van der Waals epitaxial growth process, leading to an atomically abrupt and smooth Bi2Se3-PbSe heterointerface. Benefiting from the prominent photosensitivity in narrow-gap PbSe and the ultrafast charge transport in topological insulator Bi2Se3, high photosensitivity and fast response are simultaneously observed in the as-fabricated photodetectors. Responsivity and detectivity are 31.4 AW−1 and 1.7 × 1011 cmHz0.5 W−1 respectively. Rising and falling time are 240 μs and 500 μs respectively. In this structure, the appropriate band alignment of Bi2Se3-PbSe heterojunction and the photogating effect could synergistically utilize the advantages of both Bi2Se3 and PbSe, suggesting a potential solution to broaden the application prospect for both sides.

Mechanistic studies of oxidation and iodization of PbSe thin film sensitization for mid-infrared detection

With the resurgence of uncooled PbSe-based photodetectors and the demand for mid-wave infrared (MWIR) imaging systems, a need exists for a better understanding of the sensitization process used for photoconductive detection. A mechanistic study of the oxidation and iodization process is carried out to improve the understanding of the sensitization process with experimental measurement of film composition, morphology, and crystal structure. Comprehensive material characterization is performed for PbSe thin films processed under different sensitization conditions, and results are combined to construct a physical model of the sensitization process. The relative elemental concentration distribution found in cross-sectional energy-dispersive spectroscopy line-scans is correlated with the crystallographic data collected with x-ray diffraction and Raman measurements, respectively, to build a spatially accurate model. The different sensitization conditions are then correlated to the MWIR photoresponse. This study shows that a targeted PbSeO3 layer thickness of 400 nm formed during the oxidation process is necessary to (1) restrict the top PbI2 layer thickness to less than 200 nm, (2) regulate the iodization process, allowing trace amounts of iodine to diffuse along grain boundaries to recrystallize the PbSe base-layer, and (3) preserve the stoichiometric balance of the underlying PbSe layer. An optimum oxidation process window is identified whereby too thick, as well as too thin, of a PbSeO3 layer, both result in a thick PbI2 top layer and a thin PbSe base-layer. This work also shows that PbSeO3 iodizes to form PbI2 at a rate of ∼100 nm/min at 325 °C while pure PbSe and Se-poor PbSe iodizes nearly 5× faster than PbSeO3. Overall, the oxidation step is necessary for oxygen diffusion into PbSe thin film grain boundaries and to control the iodine diffusion rate. The iodization step is necessary to form a PbI2 surface passivation layer, formation of a newly identified compound within sensitized PbSe (Pb3Se2O6I2), and incorporation of iodine into PbSe thin film grain boundaries. We identify and explain the narrow oxidation process window and iodization conditions necessary to achieve high photoconductivity.

Bright mid-infrared photoluminescence from high dislocation density epitaxial PbSe films on GaAs

We report on photoluminescence in the 3–7 µm mid-wave infrared (MWIR) range from sub-100 nm strained thin films of rocksalt PbSe(001) grown on GaAs(001) substrates by molecular beam epitaxy. These bare films, grown epitaxially at temperatures below 400 °C, luminesce brightly at room temperature and have minority carrier lifetimes as long as 172 ns. The relatively long lifetimes in PbSe thin films are achievable despite threading dislocation densities exceeding 109 cm−2 arising from island growth on the nearly 8% lattice- and crystal-structure-mismatched GaAs substrate. Using quasi-continuous-wave and time-resolved photoluminescence, we show that the Shockley–Read–Hall recombination is slow in our high dislocation density PbSe films at room temperature, a hallmark of defect tolerance. Power-dependent photoluminescence and high injection excess carrier lifetimes at room temperature suggest that degenerate Auger recombination limits the efficiency of our films, although the Auger recombination rates are significantly lower than equivalent III–V bulk materials and even a bit slower than expectations for bulk PbSe. Consequently, the combined effects of defect tolerance and low Auger recombination rates yield an estimated peak internal quantum efficiency of roughly 30% at room temperature, unparalleled in the MWIR for a severely lattice-mismatched thin film. We anticipate substantial opportunities for improving performance by optimizing crystal growth as well as understanding Auger processes in thin films. These results highlight the unique opportunity to harness the unusual chemical bonding in PbSe and related IV–VI semiconductors for heterogeneously integrated mid-infrared light sources constrained by tight thermal budgets in new device designs.