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Effect of Ag incorporation on structural and opto-electric properties of pyrolized CdO thin films
摘要： We have investigated the structure, morphology and opto-electric properties of CdO and Ag-incorporated CdO thin films prepared by chemical spray pyrolysis (CSP) method. The X-ray diffraction (GIXRD) study confirms that CdO samples are highly polycrystalline with cubic structure. The AFM study shows smooth surfaces both for CdO and Ag-CdO thin films. The direct band gap energy varies from 2.25 to 2.50 eV depending on Ag content in the films. Urbach energy reversal in optical band gap indicates that several localized states are present above Fermi level or near at the conduction band. The optical properties, such as refractive index, optical conductivity and nonlinear optical susceptibility, are found dependent on Ag content. A combined effect on the transport properties has been observed with the incorporation of Ag in CdO. The metal-like electric conduction of CdO film has been removed up to a temperature Tc for Ag doping. The n-type carrier concentration of CdO is reduced with increasing Ag content and the concentration is of the order of ~ 1020 cm?3.
关键词： Band gap,Activation energy,Thin films,XRD,Urbach tail
更新于2025-09-23 15:21:21
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Observation and implications of the Franza??Keldysh effect in ultrathin GaAs solar cells
摘要： Voltage-dependencies were observed in the external quantum efficiency (EQE) spectra of ultrathin GaAs solar cells. The subbandgap tail was shown to increase going from forward to reverse bias, while at energies above the bandgap, voltage-dependent oscillations in the EQE were measured. Using optical simulations, it is irrefutably shown that the voltage-dependencies are caused by the Franz-Keldysh effect, that is, an electric field-dependent absorption coefficient near the bandgap. The dependency on voltage of the subbandgap tail is demonstrated to be strongest in thin-film cells with a textured rear mirror, since the absorptivity below the bandgap is enhanced by light trapping. The voltage-dependent subbandgap tail has important implications for the use of the reciprocity relation between photovoltaic quantum efficiency and electroluminescence. It is shown that the radiative limit for the open-circuit voltage of thin-film cells integrated with light management schemes can be underestimated by more than 25 mV. Consequently, these cells may be assumed to be closer to the radiative limit than they really are.
关键词： Urbach tail,Franz-Keldysh effect,reciprocity,textured solar cells,ultrathin gaas
更新于2025-09-23 15:21:01
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Influence of cobalt-doping on the optical properties of zinc tris–thiourea sulfate (ZTS) single crystal
摘要： Zinc tris-thiourea sulfate (ZTS) single crystals, pure and doped with different concentrations of cobalt, were synthesized and grown by the slow evaporation technique of supersaturated aqueous solutions at 315 K. Co2+ concentration in the solution was 2, 4 and 6 mol%. Optical transmittance was measured for the obtained crystals as a function of wavelength in the range of 190–900 nm. The present investigation shows that doping ZTS crystal with Co2+ changes the values of optical transmittance, cut off wavelength, absorption coefficient of ZTS crystal exhibits an exponential dependence on photon energy following Urbach relation. Doping ZTS crystal with Co2+ modifies its optical properties. The absorption coefficient, optical energy gap, Urbach tail energy and steepness parameter. The changes are systematic i.e. the mentioned optical parameters increase or decrease continuously with increasing Co2+ concentration in the growth solution. The electrical conduction of ZTS crystal is increased with cobalt doping. The Urbach tail energy changes reversely with the optical energy gap.
关键词： ZTS crystal,cobalt-doped,urbach tail energy,optical energy gap,steepness parameter
更新于2025-09-10 09:29:36
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Band-fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors: a dimensionless joint density of states analysis
摘要： We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless Joint Density of States formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p-type GaAs and nano-crystalline Ga1?xMnxN, as examples for direct bandgap materials, as well as amorphous Si:Hx, SiC:Hx and SiNx, are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge.
关键词： band-fluctuations model,fundamental absorption,disordered semiconductor materials,absorption edge,Joint Density of States,Urbach tail
更新于2025-09-04 15:30:14