Effects of photoexcitation on the current transport mechanism in amorphous indium selenide thin films

The effect of photoexcitation on the current transport mechanism in amorphous indium selenide thin films was studied by means of dark and illuminated conductivity measurements as a function of temperature. Analysis of the dark electrical conductivity in the temperature range 110–320 K reveals behaviour characteristic of carriers excited to the conduction band and thermally assisted variable-range hopping (VRH) at the Fermi level above 280 K and below 220 K, respectively. In the temperature range 220–280 K, a mixed conduction mechanism was observed. A conductivity activation energy of ～300 meV (above 280 K), a density of localised states (evaluated assuming a localisation length of 5 Å) of 1.08 × 10²¹ cm^?3 eV^?1, an average hopping distance of 20.03 Å (at 120 K) and an average hopping energy of 27.64 meV have been determined from the dark electrical measurements. When the sample was exposed to illumination at a specific excitation flux and energy, the values of the conductivity activation energy, the average hopping energy and the average hopping range were significantly decreased. On the other hand, the density of localised states near the Fermi level increased when the light flux was increased. Such behaviour was attributed to a reversible Fermi level shift on photoexcitation.     

Thickness induced structural changes in polystyrene films

Changes to the structure of polystyrene melt films as measured through the spectrum of density fluctuations have been observed as a function of film thickness down to the polymer radius of gyration (Rg). Films thicker than 4Rg show bulklike density fluctuations. Thinner films exhibit a peak in S(q) near q=0 which grows with decreasing thickness. This peak is attributed to a decreased interpenetration of chains resulting in an enhanced compressibility. Measurements were made using small angle x-ray scattering in a standing wave geometry designed to enhance scattering from the interior of the film compared to interface scattering.     

Contribution to the transient analyses of light induced memory on amorphous semiconductor films

Condition for memorization of amorphous As₂₀Te₇₀Ge₁₀ films by a HeCd laser light pulse (4416 Å in wavelength) was obtained. Measurement of memory transient gives evidence for light enhanced crystallization. The memory effect is influenced by heat dissipation to metal electrode as well.     

Some optical properties of amorphous and crystalline antimony trisulphide thin films

The change in optical properties accompanying the amorphous crystalline transition has been studied for antimony trisulphide thin films. The real and imaginary parts of the dielectric constant are found to be much lower for amorphous films at lower photon energies, possibly because of a large number of defect states which would mostly disturb the top of the valence band and the conduction band comprised, respectively, of chalcogen lone pair and antibonding states. The crystalline material shows some structure in the imaginary part of the dielectric constant that corresponds to interband transitions, and apparently the direct band edge is at 1.88 eV. In the edge region the power law absorption has been observed in the amorphous material from which the extrapolated optical gap has been found to be 1.7 eV.     

Simple solar cells of 3.5% efficiency with antimony sulfide‐selenide thin films

Thin films of antimony sulfide‐selenide solid solutions (Sb₂S_x Se_3–x) were prepared by chemical bath deposition and thermal evaporation to constitute solar cells of a transparent conductive oxide (FTO)/CdS/Sb₂S_x Se_3–x/C–Ag. The cell parameters vary depending on the sulfide‐selenide composition in the films. The best solar cell efficiency of 3.6% was obtained with a solid solution Sb₂S_1.5Se_1.5 prepared by thermal evaporation of the precipitate for which the open circuit voltage is 0.52 V and short circuit current density, 15.7 mA/cm²under AM 1.5G (1000 W/m²) solar radiation. For all‐chemically deposited solar cells of Sb₂S_1.1Se_1.9 absorber, these values are: 2.7%, 0.44 V, and 15.8 mA/cm², and for Sb₂S_0.8Se_2.2, they are: 2.5%, 0.38 V and 18 mA/cm². (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Surface smoothening mechanism of amorphous silicon thin films

An important concern in the deposition of thin hydrogenated amorphous silicon () films is to obtain smooth surfaces. Herein, we combine molecular-dynamics simulations with first-principles density functional theory calculations to elucidate the smoothening mechanism of plasma deposited thin films. We show that the deposition precursor may diffuse rapidly on the film surface via overcoordinated surface Si atoms and incorporate into the film preferentially in surface valleys, with activation barriers for incorporation dependent on the local surface morphology. Experimental data on smoothening and precursor diffusion are accounted for.     

Photo-induced dynamical changes in refractive index in amorphous As-S films

Compositional trends of the dynamical change in refractive index induced by band-gap illumination and its recoveries by irradiation of lower photon energy are investigated in thin films of As_xS_100?x. The magnitude of the changes is positive when x ? 35, otherwise negative, and has a maximum of 0.03 at x = 43. The experimental results suggest that the dynamical changes originate from trapping of photo-excited carriers, and are essentially related to an optical “stopping effect”.     

Nickel induced lateral crystallization behavior of amorphous silicon films

Nickel induced lateral crystallization of amorphous silicon with and without electric field has been studied. Dendritic silicon growth behavior is observed, with crystallites of a few hundred nanometers in width and up to a few microns in length. The behavior can be understood from the preferential epitaxial growth of silicon from the (1 1 1) facets of the NiSi₂ precipitate, which forms during the early stage of the annealing process. The dendritic growth fronts are different with and without electric field in the nickel induced lateral crystallization process. Electric field is found to be beneficial in increasing the lateral crystallization rate and improving the film crystallinity. Joule heating plays an important role as well to enhance the lateral crystallization.     

Photoinduced reversible changes in the electronic structure of photochromic diarylethene films

The change in the valence electronic structure upon switching of two photochromic diarylethene derivatives, i.e. 1,2-bis(2-methyl-5-p-tolylthiophen-3-yl)cyclopent-1-ene (DAE1) and 1,2-bis(5-(4-hexyloxycarbonylphenyl)-2-methylthiophen-3-yl)cyclopent-1-ene (DAE2), was measured by photoelectron spectroscopy. Switching between open and closed forms was followed in situ upon illumination. The increase of the ionization energy from the closed to the open form was 0.85 eV for DAE1 and 0.80 eV for DAE2. For DAE1, the work function also decreased by 0.25 eV upon switching, which is explained by a decrease of the intrinsic molecular dipole moment and a preferential orientation of molecules in thin films.     

Photo-induced dynamical changes in amorphous As2S3 films

Optical properties of amorphous As₂S₃ films, which have been illuminated well by bandgap light in advance, can be changed dynamically by exposing to less-bandgap light. This dynamical change has been studied in connection with its plausible relation to the reversible photo-induced change. It has been found that these changes have intimate connections with each other, and can be explained by a certain configurational diagram in a coherent fashion.     

Raman studies on local structural disorder in silicon-based amorphous semiconductor films

Raman scattering and ESR measurements were carried out for amorphous Si and amorphous Si-based alloy systems such as Si-N and Si-C. A pronounced broadening of the Si-Si To-like band of Raman spectrum is observed with an increase in the N or C content for amorphous Si-N and Si-C alloy systems. The broadening of the TO-like band for amorphous Si system as well as amorphous Si-N and Si-C systems has a good correlation with an increase in the density of dangling bonds derived from ESR measurements. The fact suggests that dangling bonds are produced in order to relax the local strain due to structural constraint and lower the total energy.     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10^?5 and 10^?9 torr, and their resistivity ? measured as a function of film thicknessd≦500Å at temperaturesT=110K andT=300K. The ?(d) characteristics of films deposited at residual gas pressures of about 10^?6 torr with condensation rates of about 1Å/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ?(d) characteristics of films deposited at 10^?8 torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ?(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ?(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.

     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10⁻⁵ and 10⁻⁹ torr, and their resistivity ∂ measured as a function of film thicknessd≦500? at temperaturesT=110K andT=300K. The ∂(d) characteristics of films deposited at residual gas pressures of about 10⁻⁶ torr with condensation rates of about 1?/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ∂(d) characteristics of films deposited at 10⁻⁸ torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ∂(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ∂(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.     

High-energy ion induced physical and surface modifications in antimony sulphide thin films

Sb₂S₃ thin films prepared by electrodeposition on indium tin oxide coated glass substrate were irradiated with 150 MeV Ni¹¹⁺ ions for various fluence in the range of 10¹¹–10¹³ ions/cm². The modifications in the structure, surface morphology and optical properties have been studied as a function of ion fluence. X-ray diffraction (XRD) analysis indicates a shift in the (2 4 0) peak position towards lower diffraction angle and a decrease in grain size with increase in ion fluence. Presence of microcracks due to irradiation induced grain splitting effect has been observed from the SEM micrograph at higher ion fluence. The optical absorbance spectrum revealed a shift in the fundamental absorption edge and the band gap energy increased from a value of 1.63 eV for as-deposited films to 1.80 eV for the films irradiated with 10¹³ ions/cm².     

Laser heterodyne measurements of photo-induced refractive-index changes in amorphous As-S films

A differential-type heterodyne interferometer has been successfully utilized for studying the refractive-index changes in As-S films under illumination. The measuring system can detect phase changes down to 1° in angle in accuracy and sensitivity. It is confirmed that illumination of the films involves two distinct factors: a thermal and an optical one. The index changes are caused only by the optical effect. The time-dependent characteristics of the index changes are explained to be closely related to the photo-darkening effect.     

The growth mechanism and supercapacitor study of anodically deposited amorphous ruthenium oxide films

In the present study, ruthenium oxide (RuO₂) thin films were deposited on the stainless steel (s.s.) substrates by anodic deposition. The nucleation and growth mechanism of electrodeposited RuO₂ film has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis by X-rays (EDAX) for structural, morphological, and compositional studies. The electrochemical supercapacitor study of ruthenium oxide thin films have been carried out for different film thicknesses in 0.5 M H₂SO₄ electrolyte. The highest specific capacitance was found to be 1190 F/g for 0.376 mg/cm² film thickness.