Ultrafast carrier dynamics in GeSn thin film based on time-resolved terahertz spectroscopy

We measure the time-resolved terahertz spectroscopy of GeSn thin film and studied the ultrafast dynamics of its photo-generated carriers.The experimental results show that there are photo-generated carriers in GeSn under femtosecond laser excitation at 2500 nm,and its pump-induced photoconductivity can be explained by the Drude–Smith model.The carrier recombination process is mainly dominated by defect-assisted Auger processes and defect capture.The firstand second-order recombination rates are obtained by the rate equation fitting,which are(2.6±1.1)×10^(-2)ps^(-1)and(6.6±1.8)×10^(-19)cm^(3)·ps^(-1),respectively.Meanwhile,we also obtain the diffusion length of photo-generated carriers in GeSn,which is about 0.4μm,and it changes with the pump delay time.These results are important for the GeSn-based infrared optoelectronic devices,and demonstrate that Ge Sn materials can be applied to high-speed optoelectronic detectors and other applications.

Structural and magnetic properties of micropolycrystalline cobalt thin films fabricated by direct current magnetron sputtering

Pure cobalt(Co)thin films were fabricated by direct current magnetron sputtering,and the effects of sputtering power and pres-sure on the microstructure and electromagnetic properties of the films were investigated.As the sputtering power increases from 15 to 60 W,the Co thin films transition from an amorphous to a polycrystalline state,accompanied by an increase in the intercrystal pore width.Simultaneously,the resistivity decreases from 276 to 99μΩ·cm,coercivity increases from 162 to 293 Oe,and in-plane magnetic aniso-tropy disappears.As the sputtering pressure decreases from 1.6 to 0.2 Pa,grain size significantly increases,resistivity significantly de-creases,and the coercivity significantly increases(from 67 to 280 Oe),which can be attributed to the increase in defect width.Corres-pondingly,a quantitative model for the coercivity of Co thin films was formulated.The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy,which is primarily attributable to increased microstress.

Numerical Study and Optimization of CZTS-Based Thin-Film Solar Cell Structure with Different Novel Buffer-Layer Materials Using SCAPS-1D Software

This study explored the performances of CZTS-based thin-film solar cell with three novel buffer layer materials ZnS, CdS, and CdZnS, as well as with variation in thickness of buffer and absorber-layer, doping concentrations of absorber-layer material and operating temperature. Our aims focused to identify the most optimal thin-film solar cell structure that offers high efficiency and lower toxicity which are desirable for sustainable and eco-friendly energy sources globally. SCAPS-1D, widely used software for modeling and simulating solar cells, has been used and solar cell fundamental performance parameters such as open-circuited voltage (), short-circuited current density (), fill-factor() and efficiency() have been optimized in this study. Based on our simulation results, it was found that CZTS solar cell with Cd0.4Zn0.6S as buffer-layer offers the most optimal combination of high efficiency and lower toxicity in comparison to other structure investigated in our study. Although the efficiency of Cd0.4Zn0.6S, ZnS and CdS are comparable, Cd0.4Zn0.6S is preferable to use as buffer-layer for its non-toxic property. In addition, evaluation of performance as a function of buffer-layer thickness for Cd0.4Zn0.6S, ZnS and CdS showed that optimum buffer-layer thickness for Cd0.4Zn0.6S was in the range from 50 to 150nm while ZnS offered only 50 – 75 nm. Furthermore, the temperature dependence performance parameters evaluation revealed that it is better to operate solar cell at temperature 290K for stable operation with optimum performances. This study would provide valuable insights into design and optimization of nanotechnology-based solar energy technology for minimizing global energy crisis and developing eco-friendly energy sources sustainable and simultaneously.

Annealing Temperature-Dependent Luminescence Color Coordination in Eu-Doped AlN Thin Films

AlN was used as a host material and doped with Eu grown on Si substrate by pulsed laser deposition (PLD) with low substrate temperature. The X-ray diffraction (XRD) data revealed the orientation and the composition of the thin film. The surface morphology was studied by scanning electron microscope (SEM). While raising the annealing temperatures from 300˚C to 900˚C, the emission was observed from AlN: Eu under excitation of 260 nm excitation. The photoluminescence (PL) was integrated over the visible light wavelength shifted from the blue to the red zone in the CIE 1931 chromaticity coordinates. The luminescence color coordination of AlN: Eu depending on the annealing temperatures guides the further study of Eu-doped nitrides manufacturing on white light emitting diode (LED) and full color LED devices.

Ultrathin Limit on the Anisotropic Superconductivity of Single-Layered Cuprate Films

Exploring dimensionality effects on cuprates is important for understanding the nature of high-temperature superconductivity.By atomically layer-by-layer growth with oxide molecular beam epitaxy,we demonstrate that La_(2−x)Sr_(x)CuO_(4)(x=0.15)thin films remain superconducting down to 2 unit cells of thickness but quickly reach the maximum superconducting transition temperature at and above 4 unit cells.By fitting the critical magnetic field(μ0H_(c2)),we show that the anisotropy of the film’s superconductivity increases with decreasing film thickness,indicating that the superconductivity of the film gradually evolves from weak three-to two-dimensional character.These results are helpful to gain more insight into the nature of high-temperature superconductivity with dimensionality.

Numerical Analysis on the Effect of n-Si on Cu(In, Ga)Se2 Based Thin-Films for High-Performance Solar Cells by 1D-SCAPS

We report the performances of a chalcopyrite Cu(In, Ga)Se2 CIGS-based thin-film solar cell with a newly employed high conductive n-Si layer. The data analysis was performed with the help of the 1D-Solar Cell Capacitance Simulator (1D-SCAPS) software program. The new device structure is based on the CIGS layer as the absorber layer, n-Si as the high conductive layer, i-In2S3, and i-ZnO as the buffer and window layers, respectively. The optimum CIGS bandgap was determined first and used to simulate and analyze the cell performance throughout the experiment. This analysis revealed that the absorber layer’s optimum bandgap value has to be 1.4 eV to achieve maximum efficiency of 22.57%. Subsequently, output solar cell parameters were analyzed as a function of CIGS layer thickness, defect density, and the operating temperature with an optimized n-Si layer. The newly modeled device has a p-CIGS/n-Si/In2S3/Al-ZnO structure. The main objective was to improve the overall cell performance while optimizing the thickness of absorber layers, defect density, bandgap, and operating temperature with the newly employed optimized n-Si layer. The increase of absorber layer thickness from 0.2 - 2 µm showed an upward trend in the cell’s performance, while the increase of defect density and operating temperature showed a downward trend in solar cell performance. This study illustrates that the proposed cell structure shows higher cell performances and can be fabricated on the lab-scale and industrial levels.

Epitaxial growth of ultrathin gallium films on Cd(0001)

Growth and electronic properties of ultrathin Ga films on Cd(0001) are investigated by low-temperature scanning tunneling microscopy(STM) and density functional theory(DFT) calculations. It is found that Ga films exhibit the epitaxial growth with the pseudomorphic 1×1 lattice. The Ga islands deposited at 100 K show a ramified shape due to the suppressed edge diffusion and corner crossing. Furthermore, the majority of Ga islands reveal flat tops and a preferred height of three atomic layers, indicating the electronic growth at low temperature. Annealing to room temperature leads to not only the growth mode transition from electronic growth to conventional Stranski–Krastanov growth, but also the shape transition from ramified islands to smooth compact islands. Scanning tunneling spectroscopy(STS) measurements reveal that the Ga monolayer exhibits metallic behavior. DFT calculations indicate that all the interfacial Ga atoms occupy the energetically favorable hcp-hollow sites of the substrate. The charge density difference analysis demonstrates that the charge transfer from the Cd substrate to the Ga atoms is negligible, and there is weak interaction between Ga atoms and the Cd substrate. These results shall shed important light on fabrication of ultrathin Ga films on metal substrates with novel physical properties.

Structure,ferroelectric,and enhanced fatigue properties of sol–gel-processed new Bi-based perovskite thin films of Bi(Cu_(1/2)Ti_(1/2))O_(3)–PbTiO_(3)

Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric properties.New Bi-based perovskite thin films Bi(Cu_(1/2)Ti_(1/2))O_(3)–PbTiO_(3)(BCT–PT) are deposited on Pt(111)/Ti/SiO_(2)/Si substrates in the present study by the traditional sol–gel method.Their structures and related ferroelectric and fatigue characteristics are studied in-depth.The BCT–PT thin films exhibit good crystallization within the phase-pure perovskite structure,besides,they have a predominant(100) orientation together with a dense and homogeneous microstructure.The remnant polarization(2P_(r)) values at 30 μC/cm^(2) and 16 μC/cm^(2) are observed in 0.1BCT–0.9PT and 0.2BCT–0.8PT thin films,respectively.More intriguingly,although the polarization values are not so high,0.2BCT–0.8PT thin films show outstanding polarization fatigue properties,with a high switchable polarization of 93.6% of the starting values after 10^(8) cycles,indicating promising applications in ferroelectric memories.

Uniform deposition of ultra-thin TiO_(2) film on mica substrate by atmospheric pressure chemical vapor deposition: Effect of precursor concentration

The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl_(4) concentration on the initial deposition of TiO_(2) on mica by atmospheric pressure chemical vapor deposition(APCVD) was investigated. The precursor concentration significantly affected the deposition and morphology of TiO_(2) grains assembling the film. The deposition time for fully covering the surface of mica decreased from 120 to 10 s as the TiCl_(4) concentration increased from 0.38%to 2.44%. The grain size increased with the TiCl_(4) concentration. The AFM and TEM analysis demonstrated that the aggregation of TiO_(2) clusters at the initial stage finally result to the agglomeration of fine TiO_(2) grains at high TiCl_(4) concentrations. Following the results, it was suggested that the nucleation density and size was easy to be adjusted when the TiCl_(4) concentration is below 0.90%.

Atomic layer deposition for nanoscale oxide semiconductor thin film transistors:review and outlook

Since the first report of amorphous In–Ga–Zn–O based thin film transistors,interest in oxide semiconductors has grown.They offer high mobility,low off-current,low process temperature,and wide flexibility for compositions and processes.Unfortunately,depositing oxide semiconductors using conventional processes like physical vapor deposition leads to problematic issues,especially for high-resolution displays and highly integrated memory devices.Conventional approaches have limited process flexibility and poor conformality on structured surfaces.Atomic layer deposition(ALD)is an advanced technique which can provide conformal,thickness-controlled,and high-quality thin film deposition.Accordingly,studies on ALD based oxide semiconductors have dramatically increased recently.Even so,the relationships between the film properties of ALD-oxide semiconductors and the main variables associated with deposition are still poorly understood,as are many issues related to applications.In this review,to introduce ALD-oxide semiconductors,we provide:(a)a brief summary of the history and importance of ALD-based oxide semiconductors in industry,(b)a discussion of the benefits of ALD for oxide semiconductor deposition(in-situ composition control in vertical distribution/vertical structure engineering/chemical reaction and film properties/insulator and interface engineering),and(c)an explanation of the challenging issues of scaling oxide semiconductors and ALD for industrial applications.This review provides valuable perspectives for researchers who have interest in semiconductor materials and electronic device applications,and the reasons ALD is important to applications of oxide semiconductors.

Corrosion characteristics of single-phase Mg-3Zn alloy thin film for biodegradable electronics

Biodegradable metals as electrodes, interconnectors, and device conductors are essential components in the emergence of transient electronics, either for passive implants or active electronic devices, especially in the fields of biomedical electronics. Magnesium and its alloys are strong candidates for biodegradable and implantable conducting materials because of their high conductivity and biocompatibility, in addition to their well-understood dissolution behavior. One critical drawback of Mg and its alloys is their considerably high dissolution rates originating from their low anodic potential, which disturbs the compatibility to biomedical applications. Herein, we introduce a single-phase thin film of a Mg-Zn binary alloy formed by sputtering, which enhances the corrosion resistance of the device electrode, and verify its applicability in biodegradable electronics. The formation of a homogeneous solid solution of single-phase Mg-3Zn was confirmed through X-ray diffraction and transmission electron microscopy. In addition, the dissolution behavior and chemistry was also investigated in various biological fluids by considering the effect of different ion species. Micro-tensile tests showed that the Mg-3Zn alloy electrode exhibited an enhanced yield strain and elongation in relation to a pure Mg electrode. Cell viability test revealed the high biocompatibility rate of the Mg-3Zn binary alloy thin film. Finally, the fabrication of a wireless heater demonstrated the integrability of biodegradable electrodes and highlighted the ability to prolong the lifecycle of thermotherapy-relevant electronics by enhancing the dissolution resistance of the Mg alloy.

The effects of radio frequency atmospheric pressure plasma and thermal treatment on the hydrogenation of TiO_(2) thin film

The effects of radio frequency(RF)atmospheric pressure(AP)He/H_(2)plasma and thermal treatment on the hydrogenation of TiO_(2)thin films were investigated and compared in this work.The color of the original TiO_(2)film changes from white to black after being hydrogenated in He/H_(2)plasma at160 W(gas temperature~381℃)within 5 min,while the color of the thermally treated TiO_(2)film did not change significantly even in pure H_(2)or He/H_(2)atmosphere with higher temperature(470℃)and longer time(30 min).This indicated that a more effective hydrogenation reaction happened through RF AP He/H_(2)plasma treatment than through pure H_(2)or He/H_(2)thermal treatment.The color change of TiO_(2)film was measured based on the Commission Internationale d’Eclairage L*a*b*color space system.Hydrogenated TiO_(2)film displayed improved visible light absorption with increased plasma power.The morphology of the cauliflower-like nanoparticles of the TiO_(2)film surface remained unchanged after plasma processing.X-ray photoelectron spectroscopy results showed that the contents of Ti3+species and Ti-OH bonds in the plasma-hydrogenated black TiO_(2)increased compared with those in the thermally treated TiO_(2).X-ray diffraction(XRD)patterns and Raman spectra indicated that plasma would destroy the crystal structure of the TiO_(2)surface layer,while thermal annealing would increase the overall crystallinity.The different trends of XRD and Raman spectra results suggested that plasma modification on the TiO_(2)surface layer is more drastic than on its inner layer,which was also consistent with transmission electron microscopy results.Optical emission spectra results suggest that numerous active species were generated during RF AP He/H_(2)plasma processing,while there were no peaks detected from thermal processing.A possible mechanism for the TiO_(2)hydrogenation process by plasma has been proposed.Numerous active species were generated in the bulk plasma region,accelerated in the sheath region,and bumped toward the TiO_(2)film,which will react with the TiO_(2)surface to form OVs and disordered layers.This leads to the tailoring of the band gap of black TiO_(2)and causes its light absorption to extend into the visible region.

Homojunction structure amorphous oxide thin film transistors with ultra-high mobility

Amorphous oxide semiconductors(AOS)have unique advantages in transparent and flexible thin film transistors(TFTs)applications,compared to low-temperature polycrystalline-Si(LTPS).However,intrinsic AOS TFTs are difficult to obtain field-effect mobility(μFE)higher than LTPS(100 cm^(2)/(V·s)).Here,we design ZnAlSnO(ZATO)homojunction structure TFTs to obtainμFE=113.8 cm^(2)/(V·s).The device demonstrates optimized comprehensive electrical properties with an off-current of about1.5×10^(-11)A,a threshold voltage of–1.71 V,and a subthreshold swing of 0.372 V/dec.There are two kinds of gradient coupled in the homojunction active layer,which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility.Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

XPS Study of Electroless Deposited Sb2Se3 Thin Films for Solar Cell Absorber Material

As a thin film solar cell absorber material, antimony selenide (Sb2Se3) has become a potential candidate recently because of its unique optical and electrical properties and easy fabrication method. X-ray photoelectron spectroscopy (XPS) was used to determine the stoichiometry and composition of electroless Sb2Se3 thin films using depth profile studies. The surface layers were analyzed nearly stoichiometric. But the abundant amount of antimony makes the inner layer electrically more conductive.

High Energy X-Ray Dosimetry Using(ZnO)_(0.2)(TeO_(2))_(0.8)Thin Film-based Real-time X-Ray Sensor

This study reports the dosimetric response of a(ZnO)_(0.2)(TeO_(2))_(0.8)thin film sensor irradiated with high-energy X-ray radiation at various doses.The spray pyrolysis method was used for the film deposition on soda-lime glass substrate using zinc acetate dehydrate and tellurium dioxide powder as the starting precursors.The structural and morphological properties of the film were determined.The I-V characteristics measurements were performed during irradiation with a 6 MV X-ray beam from a Linac.The results revealed that the XRD pattern of the AS-deposited thin film is non-crystalline(amorphous)in nature.The FESEM image shows the non-uniform shape of nanoparticles agglomerated separately,and the EDX spectrum shows the presence of Te,Zn,and O in the film.The I-V characteristics measurements indicate that the current density increases linearly with X-ray doses(0-250 cGy)for all applied voltages(1-6 V).The sensitivity of the thin film sensor has been found to be in the range of 0.37-0.94 mA/cm^(2)/Gy.The current-voltage measurement test for fading normalised in percentage to day 0 was found in the order of day 0>day 15>day 30>day 1>day 2.These results are expected to be beneficial for fabricating cheap and practical X-ray sensors.

Depth Profile Study of Electroless Deposited Sb2S3 Thin Films Using XPS for Photovoltaic Applications

Sb2S3 has gained tremendous research recently for thin film solar cell absorber material because of their easy synthesis, unique electrical and optical properties. The stoichiometry and composition of electroless Sb2S3 thin films were analyzed using XPS depth profile studies. The surface layers were found nearly stoichiometric. On the other hand, the inner layer was rich in antimony composition making it more conductive electrically.

Cascade excitation of vortex motion and reentrant superconductivity in flexible Nb thin films

High quality Nb films were successfully prepared on both flexible polyimide(PI)and rigid Al2O3substrates and their transport properties were systematically studied at various applied currents,external magnetic fields,and sample orientations.It is found that a curved Nb/PI film exhibits quite different superconducting transition and vortex dynamics compared to the flat Nb/Al2O3film.For the curved Nb/PI film,smooth superconducting transitions were obtained at low currents,while unexpected cascade structures were revealed in theρ(T)curves at high currents.We attribute this phenomenon to the gradient distribution of vortex density together with a variation of superconductivity along the curved film.In addition,reentrant superconductivity was induced in the curved Nb/PI thin film by properly choosing the measurement conditions.We attribute this effect to the vortex pinning from both in-plane vortices and out-of-plane vortices.This work reveals the complex transport properties of curved superconducting thin films,providing important insights for further theoretical investigations and practical developments of flexible superconductors.

Efficient electrooxidation of biomass-derived aldehydes over ultrathin Ni V-layered double hydroxides films

Selective upgrading of C=O bonds to afford carboxylic acid is significant for the petrochemical industry and biomass utilization.Here we declared the efficient electrooxidation of biomass-derived aldehydes family over NiV-layered double hydroxides(LDHs) thin films.Mechanistic studies confirmed the hydroxyl active intermediate(-OH*) generated on the surface of NiV-LDHs films by employing electrochemical impedance spectroscopy and the electron paramagnetic resonance spectroscopy.By using advanced techniques,e.g.,extended X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy,NiV-LDHs films with 2.6 nm could expose larger specific surface area.Taking benzaldehyde as a model,high current density of 200 mA cm^(-2)at 1.8 V vs.RHE,81.1% conversion,77.6% yield of benzoic acid and 90.8% Faradaic efficiency were reached,which was superior to most of previous studies.Theoretical DFT analysis was well matched with experimental findings and documented that NiV-LDHs had high adsorption capacity for the aldehydes to suppress the side reaction,and the aldehydes were oxidized by the electrophilic hydroxyl radicals formed on NiV-LDHs.Our findings offer a universal strategy for the robust upgrading of diverse biomass-derived platform chemicals.

Investigation of Sprayed Lu2O3 Thin Films Using XPS

Spray pyrolysis method was used to deposit Lutetium Oxide (Lu2O3) thin films using lutetium (III) chloride as source material and water as oxidizer. Annealing was carried out in argon atmosphere at 450°C for 60 minutes of the films. To investigate the composition and stoichiometry of sprayed as-deposited and annealed Lu2O3 thin films, depth profile studies using X-ray photoelectron spectroscopy (XPS) was done. Nearly stoichiometric was observed for both annealed and as-deposited films in inner and surface layers.

XPS Depth Profile Study of Sprayed Ga2O3 Thin Films

Ga2O3 thin films were fabricated by spray pyrolysis method using gallium acetylacetonate as source material and water as oxidizer. The films were annealed at 450°C for 60 minutes in argon atmosphere. X-ray photoelectron spectroscopy (XPS) depth profile studies were carried out to analyze the stoichiometry and composition of sprayed as-deposited and annealed Ga2O3 thin films. Surface layers and the inner layers of as-deposited and annealed films were found nearly stoichiometric.