Defect Density Research Articles

Modeling the effects of electron irradiation on graphene drums using the local activation model

We study the effects of electron irradiation on suspended graphene monolayers and graphene supported on SiO2 substrates in the range 5.0 × 1015–4.3 × 1017 electrons/cm2. The suspended graphene monolayers are exfoliated over SiO2 substrates containing micrometer-sized holes, with graphene completely covering the hole, and are referred to as graphene drums. The irradiation was performed using a scanning electron microscope at 20–25 keV electron energy. We observe a two-stage behavior for the ID/IG, ID′/IG, and ID/ID′ ratios as a function of the average distance between defects, LD, where ID, IG, and ID′ are the intensities of the Raman D, G, and D′ peaks, respectively. Good fits to the dependence of the ratios on LD are obtained using the local activation model equation. The fits are used to characterize the defects at high defect densities. We also carried out annealing studies of samples irradiated to the first stage and used an Arrhenius plot to measure activation energies for defect healing, Ea. We measured Ea = 0.90 eV for the graphene drums, consistent with the hydroxyl groups; for supported graphene, we measured Ea = 0.36 eV, consistent with hydrogen adsorbates. We also studied the surface of the drums using atomic force microscopy and found no observable holes after irradiation and annealing. Our results show that the local activation model is useful in characterizing the defects in graphene drums.

Design and simulation of CsPb.625Zn.375IBr2-based perovskite solar cells with different charge transport layers for efficiency enhancement

In this work, CsPb.625Zn.375IBr2-based perovskite solar cells (PSCs) are numerically simulated and optimized under ideal lighting conditions using the SCAPS-1D simulator. We investigate how various hole transport layers (HTL) including Zn3P2, PTAA, MoS2, MoO3, MEH-PPV, GaAs, CuAlO2, Cu2Te, ZnTe, MoTe2, CMTS, CNTS, CZTS, CZTSe and electron transport layers (ETL) such as CdS, SnS2, ZnSe, PC60BM interact with the devices’ functionality. Following HTL material optimization, a maximum power conversion efficiency (PCE) of 16.59% was observed for the FTO/SnS2/CsPb.625Zn.375IBr2/MoS2/Au structure, with MoS2 proving to be a more economical option. The remainder of the investigation is done following the HTL optimization. We study how the performance of the PSC is affected by varying the materials of the ETL and to improve the PCE of the device, we finally optimized the thickness, charge carrier densities, and defect densities of the absorber, ETL, and HTL. In the end, the optimized arrangement produced a VOC of 0.583 V, a JSC of 43.95 mA/cm2, an FF of 82.17%, and a PCE of 21.05% for the FTO/ZnSe/CsPb.625Zn.375IBr2/MoS2/Au structure. We also examine the effects of temperature, shunt resistance, series resistance, generation rate, recombination rate, current-voltage (JV) curve, and quantum efficiency (QE) properties to learn more about the performance of the optimized device. At 300 K, the optimized device provides the highest thermal stability. Our research shows the promise of CsPb.625Zn.375IBr2-based PSCs and offers insightful information for further development and improvement.

Enhancing Flexibility, Long-Term Stability, and Efficiency in Full Air Fabricated Perovskite Solar Cells via Multifunctional Fluorinated Polyurethane Additives.

Perovskite films often suffer from surface and grain boundary defects, including uncoordinated ions, lattice distortions, and dangling bonds, coupled with lattice distortions due to solvent volatilization anisotropy and the thermal expansion coefficient. Such defects severely compromise both the photovoltaic efficiency and long-term solar cell stability. Here, fluorinated polyurethane (FPU) was synthesized and introduced into the perovskite precursor as a multifunctional additive. Excess Pb2+ ions interact with the carbonyl group (C═O) of FPU, thereby reducing nonradiative recombination. The perovskite and FPU form various hydrogen bonds via MA+ with F and -NH with -I. This multiplies the passivation of grain boundary defects, increases grain size, reduces defect density, releases residual lattice stress, and facilitates charge transport. Accordingly, the power conversion efficiency of the FPU-modified perovskite solar cells (PSCs) on rigid substrates and flexible substrates reached 21.18 and 17.76%, respectively. Notably, the long-chain C-F compound, which constructs a moisture-resistant barrier, could inhibit moisture corrosion in the perovskite films. After 2000 h of storage at ambient temperature in dark, the PSCs's initial efficiency still remained 82%. Additionally, after it undergoes 300 bending cycles (r = 0.7 cm), the device maintains 92.4% of its initial efficiency.

Effect of Different Molten Salts on Structure and Water Splitting Performance of Al-Doped Fillet Polyhedral SrTiO3.

Strontium titanium (SrTiO3) is a promising photocatalyst, but enhancing the separation, migration, and utilization of photocarriers, requires SrTiO3 with exposed anisotropic facets and minimal defect density. Here, we used NaCl and SrCl2 as fluxes to synthesize fillet polyhedral SrTiO3 particles, with Al3+ selectively adsorbed as the morphology regulator on high-energy crystal facets. Notably, Al-doped SrTiO3 synthesized in SrCl2 exhibits regular polyhedral morphology with {100}, {110}, and high-index {112} facets, showing high surface activity, low internal defect density, and superior photocatalytic performance. The excellent performance is attributed to the spatial separation of photocarriers on different crystal facets. In situ photodeposition experiments confirmed that photogenerated electrons were concentrated on the {100} facets, while holes were concentrated on the {110} and {112} facets, effectively impeding recombination. After loading RhCrOx/CoOx, Al-doped SrTiO3 synthesized in SrCl2 achieves a hydrogen evolution rate of 255µmol h-1, 64 times higher than that of Al-doped SrTiO3 synthesized in NaCl. Additionally, increasing amounts of cocatalysts further enhances the photocatalytic performance, with the average hydrogen evolution rate of SrTiO3 reaching 319µmol h⁻¹, an apparent quantum yield of 3.5% at 365nm, and a solar-to- hydrogen value of 0.181%. This discovery offers new insights into designing efficient photocatalysts for hydrogen production.

Geomorphic characterization by integrating automated approaches for sustainable land use planning in the earthquake-prone Himalayan region of Uttarakhand, India

This study leverages two cutting-edge automated landform classification approaches—Topographic Position Index (LCTPI) and Geomorphon (LCGm)—to map and categorize landforms in Uttarakhand, a strategically vital region in the Himalayas frequently impacted by natural hazards. Situated at the subduction boundary of the Indian and Eurasian tectonic plates, Uttarakhand's complex landscape demands innovative approaches for sustainable land use planning. Our analysis links classified landforms to critical factors such as slope, geology, soil types, land use land cover (LULC) patterns, fault density, and regional seismicity. Results reveal that high ridges, deep valleys (LCTPI), and slopes (LCGm), predominantly covered by trees and rangelands, are associated with lithosols and dystric cambisols soil types from the Precambrian period. In contrast, flat areas, shoulders, footslopes, U-shaped valleys, open slopes, and mild slope ridges, mainly used for agriculture and urban development, exhibit lower seismic activity. Notably, shallow earthquakes are more frequent in deep valleys and high ridges, which have low to moderate fault density and are majorly occupied by trees and rangelands. This research offers a robust framework for geomorphic characterization that can be adapted to other regions, despite the inherent limitations of automated studies, such as DEM resolution and neighbourhood cell size. Our approach supports sustainable land use planning, biodiversity preservation, natural resource management, and disaster risk reduction, ultimately fostering resilient futures in the built environment. This study emphasizes the necessity of integrating geomorphic insights into the planning process to mitigate natural hazards and enhance environmental sustainability in the Himalayan region by providing actionable insights for land use planners and policymakers.

Application of ion modification for alteration of anode materials based on ZnO/CoZn nanostructures

During the conducted studies, it was established that the use of ion modification by irradiation with O+ and Ar+ ions makes it possible to elevate the degradation resistance of anode materials due to the effect of vacancy defect creation, the density of which varies with the irradiation fluence. At the same time, the analysis of changes in the band gap and the optical density value, expressing changes in structural distortions, revealed that ion irradiation leads to a rise in the stability of the preservation of electronic properties during long-term resource tests, which are inextricably linked with the degradation of ZnO/CoZn nanostructures due to oxidation processes as a result of lithiation. During assessment of changes in the parameters of the band gap and optical density of the samples after resource tests, it was found that the observed growth in these indicators is due to oxidation processes and partial amorphization due to the formation of oxide inclusions in the structure of nanowires, the presence of which is due to the interaction of nanostructures with the electrolyte over a long period of time during charging/discharging, which results in near-surface layer degradation due to the introduction of oxygen, and in the case of a long service life, to the formation of oxide inclusions that elevate the density of defects and vacancies in the structure. According to tests of synthesized ZnO/CoZn nanostructures as anode materials, it was found that the use of O+ and Ar+ ions not only leads to a growth in the degradation resistance of capacitive characteristics during long-term tests, but also to the stability maintenance of indicators with a reversible decrease in the charging rate at charging rate variation.

Achieving Over 30% Efficiency Employing a Novel Double Absorber Solar Cell Configuration Integrating Ca3NCl3 and Ca3SbI3 Perovskites

Perovskites are particularly appealing solar absorber materials in the realm of photovoltaic (PV) technology due to their remarkable optical properties, low cost, increased efficiency, and lightweight design. This study proposes a structure that combines a double perovskite absorber layer (DPAL) of Ca3NCl3 and Ca3SbI3 with an electron transport layer (ETL) and hole transport layer (HTL) of CdS and CBTS via SCAPS-1D. Our research also demonstrated that the perovskite solar cell (PSC) with DPAL performs much better with the addition of HTL and is more efficient than single-layer PSCs. This paper thoroughly examines the effect of thickness, doping levels, and defect densities of each layer on electrical parameters like VOC, JSC, FF, and PCE. Additionally, it shows the J-V and QE characteristics and thoroughly examines the effects of temperature. With a DPAL of 24.43%, two solar cells built around a single absorber have achieved their maximum efficiency of 17.19% and 18.07%, respectively. Using CBTS HTL with Al/FTO/CdS/dual absorber (Ca3SbI3/Ca3NCl3)/CBTS/Ni structure, this study achieves an optimized efficiency of up to 30.22% with VOC of 1.39 V, FF of 88%, and JSC of 24.75 mAcm-2. This research may offer crucial information and a practical plan for creating an affordable Ca3SbI3/Ca3NCl3 thin-film solar cell.

CsF Improved Buried Interface for Efficient and Stable Inverted All-inorganic CsPbI2.85Br0.15 Perovskite Solar Cells

All-inorganic CsPbIxBr3-x is frequently used as the top cells in tandem devices due to its tunable bandgap, making it highly promising for future development. However, CsPbIxBr3-x films typically contain numerous defects at the interfaces and grain boundaries, significantly hindering carrier transport and thus reducing the device performance. Interface modification is commonly employed to passivate defects and enhance carrier transport at the interfaces. In this work, CsF was used to modify the buried interface between the perovskite film and self-assembled monolayers (SAMs). The interaction between fluoride ions (F⁻) and uncoordinated Pb2⁺ contributed to reduce defect density, enhance crystallization quality, and suppress non-radiative carrier recombination at buried interface. Consequently, the efficiency of inverted CsPbI2.85Br0.25 PSCs with CsF improved from 16.15% to 18.24%, compared to the control device. Moreover, the unencapsulated CsF-modified device retained 89% of its initial efficiency after storing for 600 h in ambient air with room-temperature and relative humidity (RH) of 20%. This demonstrates that CsF modification significantly enhances both the performance and stability of CsPbI2.85Br0.15 perovskite solar cells.

Epitaxial films and devices of transparent conducting oxides: La:BaSnO3

This paper reviews recent developments in materials science and device physics of high-quality epitaxial films of the transparent perovskite La-doped barium stannate, La:BaSnO3. It presents current efforts in the synthesis science of epitaxial La:BaSnO3 films for achieving reduced defect densities and high electron mobility at room temperature. We discuss the scattering mechanisms and the route toward engineering defect-free epitaxial La:BaSnO3 heterostructures. By combining chemical surface characterization and electronic transport studies, special emphasis is laid on the proper correlation between the transport properties and the electronic band structure of La:BaSnO3 films and heterostructures. For application purposes, interesting optical properties of La:BaSnO3 films are discussed. Finally, for their potential application in oxide electronics, an overview of current progress in the fabrication of La:BaSnO3-based thin-film field-effect transistors is presented together with recent progress in the fundamental realization of two-dimensional electron gases with high electron mobility in La:BaSnO3-based heterostructures. Future experimental studies to reveal the potential deployment of La:BaSnO3 films in optoelectronic and transparent electronics are also discussed.

Numerical modelling of lead-free perovskite photodetector with GO as ETM and Cz-N as HTM

Photodetectors (PD) are optoelectronic devices that can convert optical signal into electrical signals via the photoelectric effect. A model of CsSn0.5Ge0.5I3 based nip perovskite photodetector (PePd) with graphene oxide (GO) as electron transport material (ETM) and carbazole unit with naphthalene (Cz-N) is used as hole transport material (HTM) are established. The device configuration was analysed using solar cell capacitance simulator-1 dimensional (SCAPS-1D). The effects of absorber thickness, defect density of CsSn0.5Ge0.5I3, metal work function and operating temperature on device architecture have been investigated. For the incident light between 800-820 nm, a maximum responsivity and detectivity 0.65 A/W and 3.6×1013 Jones are obtained respectively. This simulation results will assist in the future research on high-performance lead-free perovskite photodetectors.

Regulating Compressive Strain Enables High‐Performance Tin‐Based Perovskite Solar Cells

AbstractTin (Sn)‐based perovskites have emerged as promising alternatives to lead (Pb)‐based perovskites in thin‐film photovoltaics due to their comparable properties and reduced toxicity. Strains in perovskites can be tailored to modulate their optoelectronic properties, but mechanisms for the effects of strains on Sn‐based perovskite films and devices are unrevealed and corresponding strain engineering is unexplored. Herein, a strain engineering strategy is developed through incorporating 4‐fluorobenzylammonium halide salts (FBZAX, X = I, Br, Cl) into the perovskite precursor to regulate the strain effects in resultant Sn‐based perovskite films. It is found that a moderate level of compressive strain achieved by FBZABr alleviates the dislocations within perovskites to enhance carrier transport and reduces the defect density to prolong carrier lifetime. These improvements enable a champion efficiency exceeding 14% of Sn‐based perovskite solar cells with excellent operational stability.

Achieving 31.16 % efficiency in perovskite solar cells via synergistic Dion-Jacobson 2D-3D layer design

Among environmental friendly energy sources solar energy is prominent one that can be harnessed via photovoltaic (PV) cells. The hybrid organic & inorganic perovskite solar cells (PSCs), have shown appealing PV performance. Halide-based perovskites (PVSK) offer several advantages, including low cost, high efficiency, and ease of fabrication. However, there are stability issues with these 3D perovskite materials. The solar device based on 2D PVSK materials are being used more and more in modern applications to address these problems. Ruddlesden-Popper (RP) & Dion-Jacobson (DJ) phases are the two main forms of 2D PVSK. These materials offer significantly greater stability compared to 3D perovskites, making them a promising alternative. In this study, we combine 2D and 3D perovskites to strengthen both reliability as well as efficiency of 3D PSCs. The present work explores the combined effect of DJ 2D-3D PVSK layers on device performance. The DJ 2D material used is PeDAMA4Pb5I16, while the 3D material is the lead-free, stable CsGeI3-xBrx (with x = 1). The optimized solar cell structure developed in this work consists of (Au/Cu2O/PeDAMA4Pb5I16/CsGeI3-xBrx/PCBM/FTO). A thorough analysis was performed on the impact of various ETLs and HTLs, as well as factors such as defect density (Nt), 2D-3D layer thickness, shallow acceptor density (NA), series (RS) and shunt resistances (RSh), and temperature variations. In the present work, PCE has significantly improved, reaching an amazing 31.16 %. Other noteworthy metrics include a JSC 22.55 mA.cm−2, FF 88.47 % and VOC 1.5617 V, all demonstrating exceptional performance. These results demonstrate the effectiveness of our approach in strengthening the efficiency and performance of DJ 2D-3D PSCs, highlighting their potential for future applications.

Sn-Pb Perovskite with Strong Light and Oxygen Stability for All-Perovskite Tandem Solar Cells.

Research on mixed Sn-Pb perovskite solar cells (PSCs) is gaining significant attention due to their potential for high efficiency in all-perovskite tandem solar cells. However, Sn2+ in Sn-Pb perovskite is susceptible to oxidation, leading to a high defect density. The oxidation primarily occurs through two pathways: one involving a reaction with oxygen, and the other related to iodine defects, which generate I2 and further accelerate the oxidation of Sn2⁺, greatly reducing stability. First, to tackle the photo-stability issues caused by iodine defects, amber acid (AA) is screened as the additive. The Carboxyl group on AA can strongly coordinate with Sn2+, reinforcing the Sn─I bond and electrostatically interacting with negatively charged defects. This interaction inhibits the photoinduced formation of I2 and the subsequent oxidation of Sn2+, thereby enhancing the stability of Sn─Pb PSCs under continuous illumination. Building on the foundation of AA, a reductive sulfhydryl group is introduced to synthesize thiomalic acid (TA). It inhibits the formation of Sn4+ in both the perovskite precursor and the perovskite film, thereby improving air stability while maintaining strong photostability. Consequently, single PSCs achieved a champion efficiency of 22.7%. The best-performing two-terminal all-perovskite tandem solar cell achieved a power conversion efficiency of 28.6% with improved operational stability.

A comprehensive investigation involving numerous HTL and ETL layers to design and simulate high-efficiency Ca3AsI3-based perovskite solar cells

A lot of people are interested in inorganic cubic Calcium-Arsenic-Iodide perovskites because of their unique electronic, structural, and visual properties. This research explores new hybrid perovskite solar cells (HPSCs) based on Calcium-Arsenic-Iodide (Ca3AsI3) with various wide-energy-gap chalcogenide electron transport layers (ETLs) (IGZO, ZnO, SnO2, and TiO2) and several hole transport layers (HTLs) (Sb2S3, P3HT, and CuO). Initially, the optimal ETL was selected, and its thickness was varied in the SCAPS-1D simulator to determine its impact on device performance. A detailed study was carried out on three devices (device-I (Al/FTO/ZnO/Ca3AsI3/Sb2S3/Ni), device-II (Al/FTO/ZnO/Ca3AsI3/P3HT/Ni), and device III (Al/FTO/ZnO/Ca3AsI3/CuO/Ni)) using the most promising ETL, which was ZnO. The effects of key parameters like doping concentration, layer depth, defect density, operating thermal level, and interface defect density were thoroughly investigated. Finally, a comprehensive investigation of several presented composite structures was conducted to establish the benchmark for the latest effective Ca3AsI3-based photocell. The top power conversion efficiency (PCE) achieved 29.12 % for the device −I, having a value of VOC 1.281 V, a value of JSC 25.387 mA/cm2, and a value of fill factor (FF) 89.48 %. In evaluation, PCEs of 26.39 % and 21.25 % were acquired for devices II and III, respectively. Furthermore, quantum efficiency (QE%), the electron hole, the generation, recombination rates, and series-shunt resistance characteristics were examined in detail. Therefore, the device-I exhibits great promise for integration into Ca3AsI3-based hybrid perovskite high-performance photovoltaic devices.

Effect of mechanical ball milling on the microstructure and radiation shielding performance of nano-PbO

This study probes the shielding efficacy of nano-PbO, examining the effects of milling on its microstructure and the consequences on X- and gamma-ray absorption. Characterization techniques, including XRD, Raman spectroscopy, TEM, and positron annihilation spectroscopy of commercial (milled for 10, 20, and 40 h) samples, as well as the synthesized PbO, reveal that milling induces a partial phase transformation from orthorhombic to tetragonal, alters particle morphology, and increases pore volume. Notably, milling does not significantly affect X-ray attenuation. The growing particle size with lower surface area, reduction of vacancy-type defects, and expanded pore size resulting from ball milling negatively influenced the probability of interaction of gamma-rays (<250 keV). Principal component analysis highlights the interplay between particle size, surface area, defect density, and pore size in determining shielding efficacy. This investigation underscores the importance of considering multiple parameters, beyond particle size, to optimize the radiation shielding performance of any material.

Numerical analysis and optimization of photovoltaic performance of Sb2Se3 based photocathode

Antimony selenide (Sb2Se3) based heterojunction photocathodes have recently received an increased attention, largely due to their outstanding performances for hydrogen production through photoelectrochemistry (PEC) water splitting. The PEC water splitting process encompasses both physical and electrochemical processes. The physical process is capable of generating a photo-voltage, which can drive the photo-generated electrons transport to the electrode/electrolyte interface through the p-n junction. However, unlike traditional photovoltaic device, the protective layer and co-catalyst will also affect the electrical performance of device, resulting in a decrease in PEC performances and stability. How to optimize the electrical properties of the photoelectrode is a concern. In this work, devoted to Sb2Se3/TiO2 photocathode structures, the photovoltaic performances of a photocathode were modeled and analyzed from three aspects: p-n junction, back contact, and transition layer between TiO2 and co-catalyst, using the SCAPS-1D software and a realistic set of material parameters. Based on reported optimization strategy, tthe interface electrical characteristics of photocathode were studied by adjusting energy band, donor/acceptor density, defect density, electron affinity, and other parameters. A low-cost and easy to implement optimization strategy was proposed, which used Cd1-xZnxS as the buffer layer between p-n junctions, W-doped TiO2 as the transition between TiO2/co-catalyst, and Sn-doped Sb2Se3 as the back surface layer to suppress the carrier recombination. The optimized photocathode can theoretically obtain photoelectric conversion efficiency of 17.01%–17.14% and a maximum Jsc of 38.79 mA/cm2, exhibiting the potential to obtain a large photocurrent in the photoelectrochemical water splitting process.

Simulating High‐Efficiency, Lead‐Free Inorganic‐Organic Perovskite Tandem Solar Cells with over 46% Efficiency

AbstractPerovskite‐based tandem solar cells (SCs) show significant potential for improving efficiency. In this study, three configurations were designed and optimized: a top cell (ITO/ZnSe/CH3NH3GeI3/CuSCN/Ni), a bottom cell (ITO/ZnSe/CH3NH3SnI3/CuI/Ni), and a tandem cell combining both. Using SCAPS‐1D, the study evaluated how the absorber layer thickness, doping concentration, and defect density affected photovoltaic (PV) performance. It also explored the influence of doping in the back surface field (BSF), interface defect densities, temperature, and back contact work function. The top cell achieved a power conversion efficiency (PCE) of 28.47%, with an open‐circuit voltage (VOC) of 1.21 V, a short‐circuit current density (JSC) of 27.17 mA/cm2, and a fill factor (FF) of 86.24%. The bottom cell reached a PCE of 18.46%, with a VOC of 0.83 V, a JSC of 27.17 mA/cm2, and an FF of 81.839%. The optimized tandem structure demonstrated a notably higher efficiency of 46.89%, with a JSC of 27.17 mA/cm2, a VOC of 2.04 V, and an FF of 84.31%. These results suggest the proposed CH3NH3GeI3/CH3NH3SnI3 tandem design could pave the way for efficient, eco‐friendly, and cost‐effective PV cells in a near future.

A Numerical Strategy for Achieving Efficiency Exceeding 32% with a Novel Lead‐Free Dual‐Absorber Solar Cell Using Ca3SbI3 and Sr3SbI3 Perovskites

This study presents a numerical approach to achieve high efficiency using a novel dual‐absorber perovskite solar cell (PSC) utilizing environmentally friendly inorganic perovskite materials focusing on the optimization of different parameters. Ca3SbI3 and Sr3SbI3 are employed as the upper and lower absorber layer, respectively, in the proposed PSC structure. The device architecture also incorporates SnS2 as the electron transport layer (ETL) and Spiro‐OMeTAD as the hole transport layer (HTL). The further investigation explores the effect of ETL and HTL thicknesses and doping concentrations on device performance, revealing significant impact on photovoltaic parameters. Using double‐graded materials of Ca3SbI3/Sr3SbI3 with ETL and HTL, the PSC in this study achieves an optimized efficiency of 32.74% with JSC of 34.17 mA cm−2, fill factor of 83.77%, and VOC of 1.14 V having an optimized level of doping 1 × 1017 cm−3 for Sr3SbI3 and 1 × 1016 cm−3 for Ca3SbI3 perovskite materials, with a thickness of 800 and 200 nm for Sr3SbI3 and Ca3SbI3, respectively, and defect density of 1 × 1012 cm−3 for both the materials at room temperature. These findings provide a blueprint for developing highly efficient and cost‐effective PSCs, emphasizing the importance of dual‐absorber configurations in surpassing limit of efficiency of single‐junction solar cells.

Comparative analysis of thermally evaporated nanoscale CdS thin film's structural, morphological, optical and nanomechanical properties

CdS nanoscale thin films were deposited on glass substrates at 1, 5 and 10 Å/s deposition rates by thermal evaporation process. The structural, morphological, compositional, optical and nanomechanical properties of CdS thin films were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), UV-vis spectrophotometer and nanoindentation. XRD diffractogram indicate that the deposited CdS thin films have hexagonal structure with preferred orientation towards (002) plane and nearly stoichiometric composition. Various crystal structure parameters like lattice constant, crystallite size, defect density, dislocation density, lattice strain, number of crystallite per unit surface, stacking fault were determined. From XRD results, the calculated crystal structure parameters such as the crystallite size, microstrain and defect density were in the range of 20.4-14.7 nm, 7.74-10.62 and 2.3-4.52 × 1011 lines/cm2, at 1, 5 and 10 Å/s deposition rates, respectively .The AFM images indicated that the film's rms surface roughnesses were 2.73 nm, 2.94 nm and 3.18 nm at 1, 5 and 10 Å/s, respectively. The SEM images indicated that the films were uniform, continuous and defect free. The EDX examination revealed that at 1 Å/s deposition rate the film was nearly stoichiometic. The optical band gaps were determined to be in the range of 2.37-2.43 eV. Nanoindentation tests evaluated the hardness, Young's modulus, creep behavior and strain rate of CdS films. Hardness evaluated to be 0.14-1.48 GPa, 0.15-2.46 GPa, and 0.21-2.55 GPa at 1,5 and 10 Å/s deposition rate, respectively for 20-50 µN load. The Young's modulus decreases 1-5 Å/s deposition rate and becomes almost constant 5-10 Å/s deposition rate at 70 µN load. The characterization of CdS thin film recommend it as a favorable window layer in applications like photovoltaic, optoelectronic, thermoelectric and solar cells.

Internal quantum efficiency of GaAsBi MQW structure for the active region of VECSELs

Internal quantum efficiency of GaAsBi MQW structure for the active region of VECSELs