H. S. Soliman

Optical properties of CulnSe2 thin films

The optical constants of vacuum-deposited CulnSe2 films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 500 to 2000 nm. The analysis of the experimental points of the absorption coefficient revealed the existence of two optical transition processes: an allowed direct transition withEg=1.03±0.01 eV and a forbidden direct transition withEf=1.254±0.001 eV. The optical constants of the films were independent of the substrate temperature.

Optical properties of AgGaSe2 polycrystalline films prepared by flash evaporation

Structural studies on AgGaSe2 films prepared in vacuum of 10-4 Pa onto glass or quartz substrates by a flash evaporation technique and annealed at 573 K for 2 h show that these films were polycrystalline and exhibited tetragonal chalcopyrite structure with a strong (112) orientation with a=0.599 nm, c=1.089 nm and (c/a)=1.816. The optical constants (the refractive index n, the absorption index k and the absorption coefficient varies as ) of polycrystalline AgGaSe2 films were determined from spectrophotometric measurements of the transmittance and reflectance carried out at normal incidence in the wavelength range 500-2000 nm. Graphical representations of surface and volume energy loss functions as well as the real optical conductivity as a function of photon energy show the existence of three possible optical transitions corresponding to 1.79, 1.95 and 2.2 eV respectively.

Effect of some growth parameters on vacuum-deposited CulnSe2 films

P-type copper indoselenide (CulnSe2) thin films were vacuum-deposited on glass substrates by a single-source thermal evaporation technique under different conditions of preparation. The structural properties of the films were investigated by X-ray diffraction and transmission electron microscopy and diffraction techniques. The dark resistivity of the deposited films was investigated as a function of film thickness, deposition rate and substrate temperature. The conductivity activation energy ranges from 0.851 to 1.01 eV depending on the deposition rate. Single-phase and stoichiometric CulnSe2 films could be deposited at low deposition rates (less than 4 nms−1). Higher deposition rates led to multiphase films containing InSe, ln2Se3, CuSe and Cu3Se2 in addition to CulnSe2.

Sensitivity of approximate formulas for determining optical constants of thin films

The sensitivity of approximate formulas for determining the optical constants of thin films using measurement of reflectancesR and transmittancesT at normal incidence have been investigated theoretically. The ranges of refractive indexn, absorption indexk,2nk (=ɛ2) andn2−k2(=ɛ1) within relative errors of 5%, 10%, and 20% may be obtained. Selected signs of (ɛ1)+ or (ɛ1)− have been determined. Validity of the condition n0A′=nsA has been also evaluated (A=1−R −T andA′=1−R′−T).

Anomalous photovoltaic effect in thin films of ZnSe obliquely deposited in vacuum

An anomalous photovoltaic effect (APE) has been observed in thin films of zinc selenide obliquely deposited in vacuum for the first time. Photovoltages of up to 70 V have been measured in some samples. The effect is influenced strongly by some experimental parameters. The changes in the photovoltages may be attributed to the film structure which has been investigated during the course of this study.

Structural and optical properties of thin films of

Thin films of of various thicknesses (94-400 nm) were prepared either on glass or on quartz substrates. X-ray diffractograms show that in a powder form or annealed samples in thin film form have a single-phase chalcopyrite tetragonal structure with lattice parameters and with and distortion parameter . However, the as-deposited films may have a polycrystalline nature with very fine crystallites. The optical constants (the refractive index n, the absorption index k and the absorption coefficient ) of thin films of either as deposited or after being annealed for 2 h at 673 K were determined using the transmission T and reflection R at normal incidence of light in the wavelength range 400-2500 nm. The refractive index in both cases (as deposited and after being annealed) exhibits anomalous dispersion in the wavelength range 400-600 nm. The permittivity was found to be 6.12 and 6.02 for as deposited and after being annealed respectively. A plot of shows that these films, whether as deposited or after being annealed, have two direct allowed optical transitions which are attributable to the splitting of the valence band.

Growth and optical properties of ZnIn2Se4 films

Thin films of ZnIn2Se4 were deposited on quartz substrates at 297 K by the conventional thermal evaporation technique. The as-deposited films were amorphous. On annealing at 623 K under vacuum for 3 h, the films crystallized with a preferred (1 1 2) orientation corresponding to the chalcopyrite-type structure. Films deposited on a quartz substrate heated to 573 K were also crystalline. The optical constants were computed from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. The analysis of the data gave a direct gap of 2.2 and 2.06 eV for the amorphous and crystallized films, respectively. The dispersion curve exhibited a peak above the absorption edge. An indirect gap of 1.8 eV for the crystallized films and a direct forbidden gap of 1.75 eV for the amorphous films were also deduced. A direct allowed transition with a gap of 2.065 eV and an indirect transition with a gap of 1.69 eV were deduced for the crystalline films deposited on the heated substrate.

Electrical resistivity of amorphous antimony trisulphide films

The electrical resistivity of amorphous antimony trisulphide films was investigated in the temperature range from 0 to 200° C. The temperature dependence of the resistivity follows the ordinary semiconducting behaviour above room temperature. The electrical band gap was found to be consistent with a mobility gap. By annealing the conductivity reduces and the slope of the conduction is increased indicating that the mobility gap is appreciably enhanced by annealing.

Optical properties of Cd3As2 polycrystalline thin films

Abstract The transmittance T and reflectance R have been measured at normal incidence of light for a set of vacuum deposited Cd3As2 thin films of different thickness in the wavelength range of 0.5–10 μm. The measured values T and R in conjunction with the film thickness were used to determine the optical constants (the refractive index n, the absorption index k and the absorption coefficient α) of the films. The lattice dielectric constant was found to be 17.6. Graphical representation of log (αhν) versus log ( 1 λ ) yielded three distinct linear regions. The first region had the photon energy range up to 0.3 eV. The second region had the photon energy range of 0.3–0.9 eV. The third region had the photon energy range of 0.95–2.1 eV. It was found that the only allowed type of optical transitions in the first region was indirect with an energy gap Eding = 0.05 eV. In the second region, the only allowed type of optical transition was direct with energy gap Egd = 0.72 eV. In the third region, the only allowed type of optical transition was direct with energy gap Egd = 1.56 eV. The last two values were confirmed throughout the graphical representation of- lm( 1 e ) = f(hv) . The existing allowed optical transitions in the above mentioned three regions were interpreted according to the LinChung model.

Structural and optical properties of Cd x Zn(1 ? x)Te thin films

AbstractSeven CdxZn(1 − x Te solid solutions with x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 were synthesized by fusing stoichiometric amounts of CdTe and ZnTe constituents in silica tubes. Each composition was used in the preparation of a group of thin films of different thicknesses. Structural investigation of the obtained films indicates they have a polycrystalline structure with predominant diffraction lines corresponding to (111) (220) and (311) reflecting planes, which can be attributed to the characteristics of growth with the (111) plane.The optical constants (the refractive index n, the absorption index k, and the absorption coefficient α) of CdxZn(1 \s -x) Te thin films were determined in the spectral range 500–2000 nm. At certain wavelengths it was found that the refractive index, n, increases with increasing molar fraction, x. It was also found that plots of α2 (hv) and α1/2(hv) yield straight lines, corresponding to direct and indirect allowed transitions respectively obeying the following two equations: