H.A. Zayed

Electrical and switching properties of InSe amorphous thin films

In this work electrical and switching properties of InSe thin films have been studied. The semiconductor compound InSe was obtained by direct synthesis from stoichiometric amounts of spectroscopically pure indium and selenium. By slow cooling of the synthesized InSe a polycrystalline material is obtained. The amorphous films were obtained by thermal evaporation under vacuum of the polycrystalline material on glass or pyrographite substrates. From electrical measurements, it was found that for all films the dark electrical resistivity decreases with an increase in film thickness and temperature. The InSe compound exhibits non-linear I–V characteristics and switching phenomena. The threshold voltage decreases with increasing annealing temperature and increases with increasing film thickness.

The composition dependence of the optical constants in amorphous SbxSe1−x thin films

Abstract The optical transmission and reflection at normal incidence of amorphous Sb x Se 1− x (0⩽ x ⩽0.9) thin films of different thickness (from 40 to 320 nm) were measured at room temperature in the wavelength region 500–1300 nm. From the obtained data, the absorption coefficient α, the extinction coefficient k , refractive index n , the optical energy gap E opt g and the valence band density of states g i were computed for different values of x . These constants were found to be independent of film thickness, but depend markedly on the value of the composition x . The analysis of the absorption coefficient data revealed the existence of two optical transition mechanisms, depending on the value of x , indirect transitions for Sb x Se 1− x thin films ( x = 0.1, 0.4, 0.5, 0.7, and 0.9) and a forbidden direct transition for x = 0.3. The optical energy gap E opt g was found to vary from 0.24 eV for ( x = 0.9) to 1.92 eV for ( x = 0). It was found that the high frequency optical constants n and k increase from 3.7 to 7.4 and from 0.32 to 0.64 respectively with increasing x from 0 to 0.9.

Transport properties of CuInS2, CuInSe2 and CuInTe2 thin films

Abstract Transport properties, namely electrical conductivity σ, Hall coefficient R H and thermoelectric power Q , have been measured for thin films of the ternary chalcopyrite compounds CuInS 2 , CuInSe 2 and CuInTe 2 as a function of temperature in the range 80–400 K. The calculated values of the carrier concentration for the three compounds showed that all films are non-degenerate p-type semiconductors. The effective mass m ∗ was found to decrease with increasing temperature. The temperature dependence of the Hall mobility for the three compounds showed that it increases with increasing temperature. The results were analysed in order to establish the conduction mechanism in these compounds.

Study of electrical and optical properties of Cd1 − xZnxS thin films

Thin films of Cd0.9Zn0.1S and CdS were prepared by thermal evaporation under vacuum of 10−6 Torr and with deposition rate of 60 nm/min. X ray diffraction studies confirm the hexagonal structure of both CdS and Cd0.9Zn0.1S films. The effect of heat treatments with or without CdCl2 enhances the grain size growth and improves the crystalline of the films. Moreover, the activation energy is decreased by heat treatment with or without CdCl2 for all thin films. The optical absorption coefficient of Cd0.9Zn0.1S thin films were determined from measured transmittance and reflectance in the wavelength range of 300 to 2500 nm. The optical absorption spectra reveal the existence of direct energy gap for these films. It was found that the optical energy gap decreases upon annealing or CdCl2 treatments.

Transport properties of SbxSe1-x thin films

The structural and electrical properties in the temperature range 76-473 K of Sbx,Se1-x (0<or=x<or=0.9) thin films grown on glass and quartz substrates and annealed in vacuum at 473 K were studied. The films were investigated by X-ray diffraction and electron microscope techniques. The results showed that SbxSe1-x alloys and annealed films with x=0, 0.1, 0.7 and 0.9 have hexagonal structure and orthorhombic structure for x=0.3, 0.4, and 0.5. From the variation of the DC electrical conductivity with temperature (76-473 K), two processes of conduction mechanism were observed (band mechanism and hopping conduction in localized states). The DC electrical conductivity was found to be of the order of 10-12 Omega -1 cm-1 to 10-2 Omega -1 cm-1 for selenium rich compositions and from 10-5 Omega -1 cm-1 to 10 Omega -1 cm-1 for the antimony rich compositions. The value of the thermoelectric power was found to be 120 mu V per degree for pure selenium and is always positive for x=0, 0.1, 0.3, 0.4 and 0.9 showing that structures are of p-type conduction, while for x=0.5 the thermoelectric power is negative and equals -440 mu V per degree, i.e. of n-type conduction.

Optical absorption behaviour of AgSbTe2 thin films

Abstract Bulk AgSbTe 2 possesses a cubic structure of NaCl type with a = 3.038 A. AgSbTe 2 thin films were prepared by thermal evaporation under vacuum (10 −6 torr). The room temperature deposited films were polycrystalline in nature and consisted of two-phases (AgSbTe 2 + Ag Te 2 ) with AgSbTe 2 as a major phase. The optical absorption behaviour of AgSbTe 2 thin films was studied. The energy gap ( E g ), the refractive index ( n ), relative permittivity ϵ′ and the dielectric loss ϵ″ were estimated for AgSbTe 2 thin films as well as the effect of heat treatment, in the wavelength range 400–2500 nm. Analysis of the absorption coefficient data revealed the existence of the indirect and allowed direct transitions with optical energy gaps E g i = 0.71 eV and E g d = 1.65 eV at 300 K. These values were found to increase with increasing annealing temperature.

Optical properties of agbise2 thin films

Abstract Thin films of AgBiSe2 were prepared by thermal evaporation in vacuum (10−6 Torr). The effect of thermal annealing either in vacuum or in a selenium atmosphere on the growth characteristics and stability of the films were studied using X-ray diffraction, transmission electron microscopy and the selected area electron diffraction techniques. It was observed that the as-deposited films (300 K) were poor crystalline. The degree of crystallinity increases with increasing the temperature from 300 to 473 K. At 500 K in vacuum two-phase films with AgBiSe2 as the major phase were formed. The optical constants of crystalline AgBiSe2 thin films were estimated as well as the effect of heat treatments and selenium vapor pressure on these constants. The analysis of the optical absorption spectra revealed the existence of two optical transition mechanisms: allowed direct and indirect transition, with optical energy gaps Edg = 1.66 eV and Eg = 0.91 eV at 300 K. These values were found to decrease with increasing annealing temperature.