E. Márquez

Universidad de Cádiz | UCA · Department of Condensed Matter Physics

Notwithstanding the significant optical applicability of PAZO polymer films, there are no accurate data about their optical characteristics. To remedy this shortcoming, in this study three PAZO polymer thin films are characterized, with dissimilar thicknesses, on glass substrates using only one UV/VIS/NIR transmittance spectrum T(λ) per sample and...

The Tauc–Lorentz–Urbach (TLU) dispersion model allows us to build a dielectric function from only a few parameters. However, this dielectric function is non-analytic and presents some mathematical drawbacks. As a consequence of this issue, the model becomes inaccurate. In the present work, we will adopt a procedure to conveniently transform the TLU...

We have in depth analyzed the refractive-index behavior and optical absorption of below-band-gap light, in order to calculate the basic parameters of the energy-band structure of thin layers of non-crystalline semiconductors. By carrying out a semi-empirical determination of the influence of the finite (non-zero) width of the valence and conduction...

In this investigation, we compare two standard optical characterization methods to analyze the material properties of amorphous silicon thin films obtained from their transmission spectra.

Several, nearly-1-µm-thick, pure, unhydrogenated amorphous-silicon (a-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the...

Three means are investigated for further increasing the accuracy of the characterization of a thin film on a substrate, from the transmittance spectrum T(λ) of the specimen, based on the envelope method. Firstly, it is demonstrated that the accuracy of characterization, of the average film thickness d¯ and the thickness non-uniformity ∆d over the i...

In this work, we study the influence of the geometry of a thin film on its transmission spectrum, as measured on amorphous As-based chalcogenide layers grown onto 1-mm-thick soda-lime-silica glass substrates. A new method is suggested for a comprehensive optical characterization of the film-on-substrate specimen, which is based upon some novel form...

Seven 1.1–1.4-μm-thick hydrogen-free amorphous‐silicon (a-Si) thin films were deposited at high rates (larger than 10 Å/s), by rf magnetron sputtering (RFMS) onto room-temperature glass substrates. The influence of argon-gas pressure on the structural and optical properties of these amorphous films has been systematically studied. We have used the...

Two RF magnetron sputtered a-Si thin films one of them several times thicker than the other are characterized by four methods. Since most literature data indicate presence of Urbach tails in the bandgap of a-Si, the two inverse synthesis methods based on the Tauc-Lorentz-Urbach model (TLUM) and the Cody-Lorentz-Urbach model (CLUM) are employed. It...

The microstructure and optical properties of TiO2 thin films, prepared by the sol-gel dip coating technique on glass substrates, were inspected. After deposition, the films were annealed at several temperatures in the 400–850 °C range and the resulting nanostructured films were studied by different techniques showing that their structural and optic...

Optical characterization of amine-solution-processed amorphous AsS 2 chalcogenide thin films by the use of transmission spectroscopy, Journal of Alloys and Compounds (2017), Abstract Amorphous thin layers with non-stoichiometric chemical composition As 33 S 67 (AsS 2) have been prepared by spin coating. This particular deposition technique is a ver...

An algorithm is proposed for computer drawing accurate envelopes of reflectance spectra R(λ), for specimens representing a thin transmitting film on a substrate. The algorithm uses only one-step smoothing the spectrum, and piecewise cubic Hermite polynomial interpolation, which is shown to be superior to cubic spline interpolation for constructing...

The present study reports the synthesis of polycrystalline ZnxCd(1-x)Te (x = 0,0.025, 0.050,0.075 and 0.100) using the chemical reaction in terms of ball milling. Ternary ZnxCd(1-x)Te thin films were grown onto glass substrates at the temperature of 373 K using thermal evaporation technique. X-ray diffraction study showed that films are polycrystal...

The accuracy of the popular graphical method of Swanepoel (SGM) for the characterization of a thin film on a substrate specimen from its interference transmittance spectrum depends on the subjective choice of four characterization parameters: the slope of the graph, the order number for the longest wavelength extremum, and the two numbers of the ex...

Agx(As0.33S0.67)100-x amorphous chalcogenide thin films have been prepared by the process of photodissolution or photodoping, reaching silver concentrations of up to 16.5 at. %. The optical constants of the photodoped thin-film samples have been calculated from the envelopes of the transmission spectra, taken at normal incidence. The dispersion of...

Exposure with bandgap light, in air, and thermal annealing at a temperature near the glass transition temperature, of thermally-evaporated amorphous As40S20Se40 thin films, were found to be accompanied by structural effects, which, in turn, lead to changes in the refractive index and shifts in the optical absorption edge. Also, clear indications of...

We have analysed in detail the effect of silver-content on the optical properties of Ag-photodoped amorphous (As0.33S0.67)100−xTex (with x = 0, 1, 5 and 10 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Agy[(As0.33S0.67)100−xTex]100−y, with y ≲ 18 at.%, were successfully...

We have analysed the effect of silver content on the optical properties of Ag-photodoped amorphous GexSb40−xS60 (with x = 10, 20 and 30 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Agy(GexSb40−xS60)100−y, with y 10 at.%, were prepared by successively photodissolving ab...

The optical dielectric response of AsxSe1-x and AsxS1-x binary glass films is studied in the frame of a model based on the distinct electronic contribution of the different building blocks occurring in glasses.

Self-organization occurring in AsxS1−x and AsxSe1−x glass alloy films reflects in their low-frequency optical dielectric response, and valuable information about the building blocks conforming their structure, can be derived from the analysis of the refractive-index dispersion data. The experimental results are discussed in the framework of the sin...

The interference modulated reflection spectra R(λ) at normal incidence for amorphous GeSe2 semiconducting films, deposited by thermal evaporation, were obtained in the spectral region from 400 nm to 2200 nm. The straightforward method proposed by Minkov, which is based on the use of the extrema of the interference fringes R(λ), has been applied in...

The optical constants and average thickness of metal-chalcogenide glass films of chemical composition CuxAs50Se50−x, with x = 5, 10 and 15 at.%, are accurately determined by a novel interferometric method, based on the optical transmission spectra at normal incidence, measured over the 300 to 2000 nm spectral region. This very useful optical method...

Amorphous films with compositions (As0.33S0.67)100−xTex (x = 0, 1, 5 and 10 at.%) and GexSb40−xS60 (x = 10, 20 and 30 at.%) have been prepared by thermal evaporation. The compositional dependences of their optical properties, with increasing Te and Ge content, respectively, are explained in terms of the modifications occurring in the film structure...

Optical transmission spectra are very sensitive to inhomogeneities of thin films. In particular, non-uniform film thickness leads to shrinking of the transmission spectrum at normal incidence. This non-uniformity has to be taken into account, because its ignorance may lead to serious errors in the calculated values of the refractive index and the f...

Germanium and silicon monoxide thin films prepared with different evaporation conditions are analysed. Substrate temperatures from 30 to 370 °C and deposition rates from 0.3 to 3.0 nm/s for SiO and from 0.5 to 1.5 nm/s for Ge films are considered. Optical constants in the mid-infrared range are derived from transmission spectra and their variation...

Amorphous chalcogenide films of stoichiometric composition As40S60 have been prepared by three different deposition techniques, namely, vacuum thermal evaporation, plasma-enhanced chemical vapour deposition (PECVD) and spin coating. Indications of film-thickness inhomogeneities were found in all samples. Thermally evaporated and chemically deposite...

An envelope method, based on the optical reflection spectrum taken at normal incidence, has been successfully applied to the geometrical–optical characterization of thin dielectric films having significant surface roughness. Such a method allows the determination of the average thickness and the refractive index of the films with accuracies better...

Amorphous chalcogenide films of chemical compositions As40S60 and As40Se60 have been prepared by plasma-enhanced chemical vapor deposition. An improved optical characterization method suitable for non-uniform thin films, which also takes into consideration the weak absorption in the substrate, has successfully been applied. The values of the averag...

Amorphous As40S60-xSex (x = 0, 20, 30, 40 and 60 at. %) films have been prepared by vacuum thermal evaporation. Values for the refractive index and the absorption coefficient of these films have been determined from their transmission spectra, measured at normal incidence, in the spectral range from 400 to 2200 nm. It has been found that the refrac...

A new method for the geometrical and optical characterization of non-uniform thin isotropic dielectric films deposited onto a transparent substrate, has been developed. The algorithm is based on using the two envelopes of the optical reflection spectrum taken at normal incidence. The method allows determining the average thickness and the refractiv...

Amorphous As40S60-xSex (x = 0, 20, 30, 40 and 60 at. %) films have been prepared by vacuum thermal evaporation. Values for the refractive index and the absorption coefficient of these films have been determined from their transmission spectra, measured at normal incidence, in the spectral range from 400 to 2200 nm. It has been found that the refrac...

A new method for the geometrical and optical characterization of non-uniform thin isotropic dielectric films deposited onto a transparent substrate, has been developed. The algorithm is based on using the two envelopes of the optical reflection spectrum taken at normal incidence. The method allows determining the average thickness and the refractiv...

This paper deals with the structural and optical properties of virgin (i.e., as-evaporated) and annealed (i.e., thermally relaxed) amorphous As40S60−xSex films (x=0, 20, 30, 40 and 60 at.%), which were prepared by vacuum evaporation. Structural properties have been inferred from the X-ray diffraction patterns and the Raman spectra of the thin-film...

Compositional dependencies of the optical properties of as-deposited amorphous As40S60−xSex films (x=0, 20, 30, 40 and 60 at.%), prepared by thermal evaporation, have been studied. The refractive index, n, and absorption coefficient, α, have been determined from the upper and lower envelopes of the transmission spectra, measured at normal incidence...

The role played by a glass substrate on the accurate determination of the optical constants and the thickness of a thin dielectric film deposited on it, when well-known envelope methods are used, is discussed. Analytical expressions for the two envelopes of the optical transmission spectra corresponding to film. with both uniform and nonuniform thi...

Annealing at a temperature near the glass transition temperature and exposure with bandgap light, in air, of thermally-evaporated amorphous As40S30Se30 films, were found to be accompanied by structural effects, which, in turn, lead to changes in the refractive index and shifts in the optical absorption edge. Also, indications of photo-oxidation wer...

Thickness inhomogeneities in thin films have a large influence on their optical transmission and reflection spectra. If not taken into account, this may lead to rather large calculated values for the absorption coefficient or the erroneous presence of an absorption-band tail, as well as to significant errors in the calculated values of the refracti...

The effect of successive annealing illumination cycles on the structural and optical properties of wedge-shaped As50Se50 amorphous chalcogenide thin films, has been studied. It is observed that illumination increases the thickness and shrinks the bandgap. Annealing of the chalcogenide films, before or after illumination, decreases the thickness. Ho...

We have analysed the effect of silver content on the optical properties of Ag-doped Ge10Sb30S60 chalcogenide glass films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of compositions Agx(Ge0.1Sb0.3S0.6)100−x, with x≲8 at.%, were obtained by successively photodissolving thin (around 10 nm) layers of silver. The opt...

Ag-x(As033S0.67)(100-x) amorphous chalcogenide thin films have been prepared by the process of photodissolution or photodoping, reaching silver concentrations of up to 16.5 at. %. The optical constants df the photodoped thin-film samples have been calculated from the envelopes of the transmission spectra, taken at normal incidence. The dispersion o...

The role played by the silicon substrate in the light-induced vitrification of As50Se50 thin films is analyzed. It is demonstrated that these films can crystallize into different structures, depending on the substrate they are attached to. Photo-oxidation when the illuminated film is deposited on silicon can be enhanced due to a chemical reaction o...

The interference modulated transmission spectra T( lambda ) at normal incidence for amorphous arsenic sulphide semiconducting films deposited by thermal evaporation were obtained in the spectral region from 300 nm up to 2000 nm. The straightforward analysis proposed by Swanepoel (1983), which is based on the use of the extremes of the interference...

Annealing (in vacuum) at a temperature near the glass transition temperature and exposure (in air) with bandgap light of thermally-evaporated As40S40Se20 amorphous chalcogenide thin films, were found to be accompanied by structural changes, which lead to changes in the refractive index and shifts in the optical absorption edge. Indications of photo...

Optical reflection spectra, at normal incidence, of amorphous semiconductor thin films of chemical composition, As40S40Se20, deposited by thermal evaporation, have been obtained in the 0.56–3.10eV spectral region. The optical constants of this glassy alloy have been determined by use of an optical characterization method, which is based only on the...

Optical-transmission spectra are very sensitive to inhomogeneities in thin films. In particular, a non-uniform thickness produces a clear shrinking in the transmission spectrum at normal incidence. If this deformation is not taken into account, it may lead to serious errors in the calculated values of the refractive index and film thickness. In thi...

Photo-vitrification of As50Se50 thin films deposited onto silicon wafer and glass substrates has been studied using X-ray diffraction, far-infrared, and differential infrared spectroscopies. The optical study of this photo-amorphization effect has been carried out by two different methods enabling the determination of the average thickness and refr...

The optical properties of ternary chalcogenide amorphous thin films of chemical composition Ge10As15Se75, deposited by vacuum thermal evaporation, have been determined and analysed. Normal-incidence optical transmission spectra have been measured in the range from 400 to 2500 nm. From these transmission spectra, the optical constants and average th...

We have analyzed the influence of rapid thermal annealing (from 300 to 1050 °C) on the optical properties of a-SiNx:H. Three compositions were investigated: x = 0.97, x = 1.43 and x = 1.55. Two different behaviors are observed depending on whether the as-grown nitrogen to silicon ratio of the samples is above or below the percolation threshold (x =...

The kinetics of the photo-induced solid-state chemical reaction of silver with amorphous As33S67 films in a conventional sandwich structure was measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflection technique. The reaction between silver and the chalcogenide layer was induced by an...

The optical constants and average thickness of metal - chalcogenide glass films of chemical composition , with x = 5, 10 and 15 at.%, are very accurately determined by a novel method, based only on the transmission spectra at normal incidence, measured over the 400 - 2200 nm spectral range. This useful optical method takes into consideration the no...

The preparation of layers of amorphous GexSe1−x (with Ge atomic concentrations x=0, 0.17, 0.25 and 0.34) by plasma-enhanced chemical vapour deposition (PECVD) using the hydrides, GeH4 and H2Se, as precursor gases is described in detail. Information concerning the structure of the films was obtained from Raman spectroscopy. The optical transmission...

S40Se20, deposited by thermal evaporation, were obtained in the 400nm to 2200nm spectral region. The optical constants of this amorphous material were computed using an optical characterization method based mainly on the ideas of Minkov and Swanepoel of utilising the upper and lower envelopes of the spectrum, which allows us to obtain both the real...

Inhomogeneities in thin films have a large influence on the optical transmission and reflection spectra. If not corrected for, this may lead to too large calculated values for the absorption coefficient or the apparent presence of an absorption band tail, as well as serious errors in the values of the refractive index and film thickness. The effect...

Exposure (in air) with bandgap light, and annealing (in vacuum) at a temperature near Tg, of As3Se2 amorphous thin films, were found to be accompanied by changes in the refractive index and shifts in the optical-absorption edge. Reversible changes were observed when cycles of annealing and exposure (and vice versa) were carried out. These reversibl...

The photo-vitrification of As50Se50 thin films deposited onto silicon wafer substrates is reported. This process, which was found to be athermal, has been studied using X-ray diffraction measurements, far infrared spectroscopy, EDAX-measurements, and scanning electron microscopy. When the crystallized films were illuminated in order to be amorphize...

Optical reflection spectra, at normal incidence, of binary chalcogenide glass thin films of chemical compositions As25S75 and Ge33Se67, deposited by thermal evaporation, were obtained in the 400 nm to 2200 nm spectral region. The optical constants of these particular amorphous materials were accurately determined using an optical characterization m...

The photo-induced shift in the optical-absorption edge and changes in the optical constants (n,k), and their dispersion in the vicinity of the absorption edge, have been studied in obliquely-deposited thin films of the GeS2 chalcogenide glass, prepared by vacuum thermal evaporation onto glass and silicon wafer substrates. Light exposure of the GeS2...

Without Abstract

In this paper we report on a study of a novel photo-induced structural effect in amorphous chalcogenide materials, namely the reversible and athermal light-induced vitrification of As50Se50 thin films. The first optical analysis of this phenomenon presented here was done by applying two different non-destructive methods. One is based on the optical...

The optical transmission spectrum of amorphous Se films prepared by plasma-enhanced chemical vapour deposition was measured over the 500 to 2000 nm spectral region. The absorption coefficient values plotted vs photon energy according to Tauc's law yielded an optical gap, Eg, of 1.94 eV. The temperature dependence of Eg was measured between 13 K and...

Abstracts are not published in this journal

Optical transmission spectra are very sensitive to inhomogeneities in thin films. In particular, non-uniform thicknesses produce a shrinking on the transmission spectrum at normal incidence. This deformation should be taken into consideration, because not doing so may lead to errors in the values of the refractive index and film thickness. This pap...

The electrical conductivity of three glassy samples from the system CuAsSe and its variation with temperature have been studied. The d.c. conductivity has been obtained from the linear current-voltage measurements, showing an Arrhenius-type dependence on temperature. The pre-exponential factor in this dependence indicates that the electrical conduc...

The results of a systematic study of the photodissolution of silver in As0.35S0.65 chalcogenide glass films are reported. The silver and chalcogenide glass films were prepared by thermal evaporation. The kinetics of the photodoping process have been investigated in detail by monitoring the time dependence of the electrical resistance of the Ag laye...