G. Perna

Optical characterization of CdSxSe1−x films grown on quartz substrate by pulsed laser ablation technique

Abstract CdS x Se 1− x alloys have been deposited on quartz substrates by means of pulsed laser ablation, a relatively new technique for growing semiconductor films. We obtained high quality polycrystalline films which present photoluminescence efficiency up to at room temperature. The dependence of the band gap on the x composition, measured by absorption spectra at 10 K, shows an upwards band gap bowing. The real part of the refractive index in the transparent region at room temperature is well described by the Sellmeier relation.

Reflectance and photoluminescence characterization of CdS and CdSe heteroepitaxial films deposited by laser ablation technique

Abstract Optical properties of CdSe and CdS films, deposited on sapphire substrate by means of pulsed laser ablation technique, have been investigated in order to study the effect of such a transparent substrate on the photoluminescence efficiency of the deposited epilayers. CdSe and CdS films present intrinsic (excitonic) emission at low temperature, differently from the same films deposited on quartz. The temperature dependence of the excitonic energy has been analyzed taking into account the contribution of both the thermal dilatation and electron–phonon interaction.

STRUCTURAL PROPERTIES AND PHOTOLUMINESCENCE STUDY OF CDSE/SI EPILAYERS DEPOSITED BY LASER ABLATION

Structural and optical characterization of CdSe thin films deposited by laser ablation technique on silicon (100)- and (111)-oriented substrates are reported. The effect of the substrate orientation on the growth and luminescence features of the two types of epilayers are investigated. Photoluminescence spectra of CdSe films measured from 10 up to 300 K and as a function of the laser excitation intensity give detailed information on the extrinsic levels localized in the forbidden gap. Temperature dependence of the energy of the n=1 exciton line has been fitted by the Varshni’s equation and by an expression containing the Bose–Einstein occupation factor for phonons. Parameters related to the electron-phonon interaction have been obtained. Temperature dependence of the broadening of exciton linewidth has been studied in terms of an expression containing both exciton-optical phonon and exciton-acoustic phonons coupling constants. Evaluated fitting parameters have shown the dominant contribution of optical ph...

Laser ablation of highly oriented CdSe thin films and CdSeCdTe multilayers on silicon substrates

Abstract The laser ablation technique has been successfully used in our laboratory for the deposition of CdSe and CdTe CdSe multilayers on Si(100) and Si(111) substrates. X-ray analysis showed that CdSe Si(111) and CdSe Si(100) films were grown in the hexagonal phase. Their orientation changed from (100) to (002) by only varying the substrate temperature from 200°C to 400°C. The same hexagonal growth was obtained in multilayers of CdSe and CdTe on Si(111). Photoluminescence spectra of CdSe films were studied as a function of the excitonic features and results on the extrinsic luminescence are reported.

Effect of disorder on the Raman scattering of CdSxSe1−x films deposited by laser ablation

Abstract We present micro-Raman spectra at room temperature of CdS x Se 1− x ternary films deposited on Si(111)-oriented substrates by means of the laser ablation technique. The lineshape of the LO phonon structure is characterized by significant asymmetry and broadening induced by disorder in the alloy. The asymmetric line profile can be described as a composite of two phonon modes, one ascribed to zone-center and the other to zone-edge phonons. Attempts to fit the experimental data to the spatial correlation model result in a poor agreement. We discuss the possibility to include into the lineshape analysis the contribution from the disorder-activated phonon density of states.

Photoluminescence analysis of laser-deposited CdS films

Abstract Temperature ( T ) dependence of photoluminescence spectra of laser ablated CdS films are presented. The analysis of spectral position and line width of the excitonic line versus T allows to calculate the critical parameters of CdS films.

Absorption and photoluminescence analysis of CdS ablated films grown on quartz substrate

Abstract CdS films have been deposited on quartz substrate by means of pulsed laser deposition. The high quality of the deposited films is demonstrated by the presence of excitonic transition in the absorption spectra. The Elliot theory has been used to explain the absorption measurements and to obtain the fundamental energy gap value as a function of the temperature. Different from previous studies on CdS films, the temperature dependence of the band gap has been analyzed by taking into account the contribution of both the thermal dilatation and electron–phonon interaction. The photoluminescence emission is dominated by near band gap recombinations which persist up to room temperature.

Temperature dependence of the red shift and broadening of the exciton line in CdSe/GaAs laser ablated heterostructures

A detailed photoluminescence investigation of the thermal red-shift and broadening of the excitonic line of CdSe films grown on bulk GaAs substrate by laser ablation technique is presented. Material parameters related to the electron-phonon interaction have been obtained by fitting the experimental data to phenomenological models. The relative contribution of both acoustic and optical phonons to the band gap shrinkage and the dominant role of impurity scattering, at low temperatures, in the excitonic line broadening are discussed.

Structural and optical properties of II−VI thin films and II−VI multilayered structures grown on silicon by laser ablation

Abstract Pulsed laser assisted deposition (PLAD) was shown to be a powerful and versatile technique to obtain highly oriented thin films of CdSe and CdSe/CdTe multilayers on silicon substrate. In multilayer deposition the choice of the buffer layer is crucial and very important if very thin layers have to be deposited in the aim of obtaining superlattices. II–VI compounds such as CdSe, CdTe, CdS were deposited by laser ablation on Si in the aim of verify which of them is the best as buffer layer. The effect of the substrate temperature on film orientation and composition has been investigated by X-ray diffraction and photoluminescence (PL) measurements. Multilayered structures were also deposited by PLAD on silicon and X-ray analysis were carried out on bilayers of CdS/CdSe/Si. Temperature dependence of photoluminescence spectra of CdSe, CdS and CdS/CdSe films on Si substrates are reported. The best resolved intrinsic photoluminescence features were obtained for films deposited on Si(111).

Photoluminescence of random GaAs/(AlGa)As Superlattices

Abstract The photoluminescence (PL) spectra of disordered superlattices (d-SL) are discussed. The experimental results evidence the existence of impurity-like states and of disorder-induced fine structures.