E. Márquez

Universidad de Cádiz | UCA · Department of Condensed Matter Physics

UV/Vis/NIR transmittance spectra T(λ) are often used for the characterization of thin films in both spectrophotometry and spectroscopic ellipsometry. T(λ) are inherently noisy due to noise generated by the measuring equipment and the environment. Nevertheless, film characterizations are usually performed either without denoising T(λ) or by smoothin...

Historically, spectroscopic techniques have been essential for studying the optical properties of thin solid films. However, existing formulae for both normal transmission and reflection spectroscopy often rely on simplified theoretical assumptions, which may not accurately align with real-world conditions. For instance, it is common to assume (1)...

To design semiconductor-based optical devices, the optical properties of the used semiconductor materials must be precisely measured over a large band. Transmission spectroscopy stands out as an inexpensive and widely available method for this measurement but requires model assumptions and reconstruction algorithms to convert the measured transmitt...

While thin film transmission spectroscopy systems can measure semiconductor optical properties, the utilized optimization-based evaluation methods often introduce variances in the results. We introduce a method of optimizing film surface shapes that reduces this uncertainty.

We present a novel Deep Learning technique based on a CNN-LSTM architecture that directly performs the optical characterization of thin-film materials from their UV-VIS-IR transmission spectra.

We present a novel Deep Learning technique based on a CNN-LSTM architecture that directly performs the optical characterization of thin-film materials from their UV-VIS-IR transmission spectra.

We present a novel Deep Learning technique based on a CNN-LSTM architecture that directly performs the optical characterization of thin-film materials from their UV-VIS-IR transmission spectra.

We present a novel Deep Learning technique based on a CNN-LSTM architecture that directly performs the optical characterization of thin-film materials from their UV-VIS-IR transmission spectra.

We present a novel Deep Learning technique based on a CNN-LSTM architecture that directly performs the optical characterization of thin-film materials from their UV-VIS-IR transmission spectra.

While thin film transmission spectroscopy systems can measure semiconductor optical properties, the utilized optimization-based evaluation methods often introduce variances in the results. We introduce a method of optimizing film surface shapes that reduces this uncertainty.

Copper-nitride (Cu3N) semiconductor material is attracting much attention as a potential, next-generation thin-film solar light absorber in solar cells. In this communication, polycrystalline covalent Cu3N thin films were prepared using reactive-RF-magnetron-sputtering deposition, at room temperature, onto glass and silicon substrates. The very-bro...

Copper-nitride (Cu3N) semiconductor material is attracting much attention as a potential, next-generation thin-film solar-light absorber in solar cells. In this communication, polycrystalline Cu3N thin films were prepared using reactive-RF-magnetron-sputtering deposition, at room temperature, onto glass and silicon substrates. The very-broadband op...

OEMT is an existing optimizing envelope method for thin-film characterization that uses only one transmittance spectrum, T(λ), of the film deposited on the substrate. OEMT computes the optimized values of the average thickness, d¯, and the thickness non-uniformity, Δd, employing variables for the external smoothing of T(λ), the slit width correctio...

Copper-nitride (Cu3N) material is attracting much attention as a potential next-generation thin-film solar-light absorber. In this work, polycrystalline Cu3N thin films were prepared using reactive-RF-magnetron sputtering, at room temperature,onto glass and silicon substrates. The optical properties of the Cu3N thin layers were studied by spectrosc...

Copper nitride (Cu3N), a metastable poly-crystalline semiconductor material with reasonably high stability at room temperature, is receiving much attention as a very promising next-generation, earth-abundant, thin film solar light absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly (greener from an environmental s...

This research presents a novel Deep Learning method to find the Swanepoel Envelopes from the transmission spectra of dielectric thin films. This method improves the efficiency and accuracy of the film’s optical characterization.

Copper nitride (Cu3N), a metastable semiconductor material, but with reasonably-high-stability at room temperature, is drawing a great deal of attention as a very promising next-generation, earth-abundant, thin-film solar absorber. Its non-toxicity, on the other hand, makes it a very attractive eco-friendly semiconducting material. In the present w...

This research presents a novel Deep Learning method to find the Swanepoel Envelopes from the transmission spectra of dielectric thin films. This method improves the efficiency and accuracy of the film’s optical characterization.

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...

Best paper of the year according to the journal “Measurement Science and Technology”, corresponding to the field of Optics.

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 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...

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...

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 films 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 =...