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Papers by Michele Begotti

Crystal Research and Technology, 2005

The d. c. electrical properties of amorphous thin films of Se85Te15 -x Pbx, prepared by vacuum de... more The d. c. electrical properties of amorphous thin films of Se85Te15 -x Pbx, prepared by vacuum deposition technique, have been studied at low and at relatively high temperatures. The dark conductivity studies show that the conductivity increases with increasing temperature at all temperature range. Two types of conduction mechanisms were found to dominate in the measured temperature range, namely band conduction through extended states (which dominates at the intermediatetemperature region) and hopping around the Fermi level (which dominates at the low-temperature region). At low temperature, the density of states and other related Mott's parameters are calculated near the Fermi level. A discontinuity, found in the curve at high temperature may be explained due to structural changes that occur near glass transition temperature. Transient photoconductivity measurements at different temperatures and intensities indicate that the decay of photoconductivity is quite slow. Thin films exhibit long-lived residual photoconductivity, called persistent photoconductivity, with an extremely slow decay rate. The persistent photoconductivity increases with an increase in intensity. Photoconductivity decay, even after subtraction of persistent photoconductivity, is found to be non -exponential suggest the presence of continuously distributed deep localised gap states in this material. Differential lifetime and carrier lifetime are also calculated.

Crystal Research and Technology, 2005

ABSTRACT The properties of Zinc-doped GaAs, grown by MOVPE employing the tertiary buthyl arsine p... more ABSTRACT The properties of Zinc-doped GaAs, grown by MOVPE employing the tertiary buthyl arsine precursor, were studied as a function of the doping level, comprised within the (1 × 1016 – 7 × 1019 cm–3) range. Hall effect measurements were performed as a function of temperature; the simultaneous analysis of the Hall hole density and Hall mobility gave the effective doping concentration, the thermal ionisation energy of the acceptor impurities and the compensation ratio. Fast Fourier Transform Photoluminescence measurements were performed on the GaAs layers; the results were correlated with those obtained from the electrical analysis. A comparison of the obtained data with the results of an analogous investigation, previously performed on intrinsically Carbon doped GaAs layers, allowed the following conclusions: a) the GaAs layers exhibit a low content of non-intentional impurities (<1014 cm–3); b) both Zinc and Carbon show a low compensation ratio; c) both Carbon and Zinc doped layers show electrical and optical properties comparable with the state of the art; d) Carbon intrinsic doping appears preferable for low-medium carrier concentrations, while Zinc appears preferable for medium-high carrier concentrations (higher than about 5 × 1017 cm–3). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Applied Surface Science, 2004

Lattice-matched, single and multiple InGaP/GaAs/InGaP quantum wells (QWs) were grown at 600 8C by... more Lattice-matched, single and multiple InGaP/GaAs/InGaP quantum wells (QWs) were grown at 600 8C by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE), with the use of the tertiarybuthylarsine (TBAs) and tertiarybuthylphosphine (TBP) group-V sources. In order to enhance the interface abruptness, different gas switching sequences were exploited during the growth of the interface, and the best results were obtained by inserting a few monolayer-thick GaAsP interlayers (IL), at the direct GaAs-on-InGaP interface. Low-temperature photoluminescence (PL), high resolution X-ray diffraction, transmission electron microscopy and photoreflectance spectroscopy analysis were performed on the grown heterostructures, to correlate the adopted growth sequence with the interface properties and the QW optical transitions.

Crystal Research and Technology, 2005

The d. c. electrical properties of amorphous thin films of Se85Te15 -x Pbx, prepared by vacuum de... more The d. c. electrical properties of amorphous thin films of Se85Te15 -x Pbx, prepared by vacuum deposition technique, have been studied at low and at relatively high temperatures. The dark conductivity studies show that the conductivity increases with increasing temperature at all temperature range. Two types of conduction mechanisms were found to dominate in the measured temperature range, namely band conduction through extended states (which dominates at the intermediatetemperature region) and hopping around the Fermi level (which dominates at the low-temperature region). At low temperature, the density of states and other related Mott's parameters are calculated near the Fermi level. A discontinuity, found in the curve at high temperature may be explained due to structural changes that occur near glass transition temperature. Transient photoconductivity measurements at different temperatures and intensities indicate that the decay of photoconductivity is quite slow. Thin films exhibit long-lived residual photoconductivity, called persistent photoconductivity, with an extremely slow decay rate. The persistent photoconductivity increases with an increase in intensity. Photoconductivity decay, even after subtraction of persistent photoconductivity, is found to be non -exponential suggest the presence of continuously distributed deep localised gap states in this material. Differential lifetime and carrier lifetime are also calculated.

Crystal Research and Technology, 2005

ABSTRACT The properties of Zinc-doped GaAs, grown by MOVPE employing the tertiary buthyl arsine p... more ABSTRACT The properties of Zinc-doped GaAs, grown by MOVPE employing the tertiary buthyl arsine precursor, were studied as a function of the doping level, comprised within the (1 × 1016 – 7 × 1019 cm–3) range. Hall effect measurements were performed as a function of temperature; the simultaneous analysis of the Hall hole density and Hall mobility gave the effective doping concentration, the thermal ionisation energy of the acceptor impurities and the compensation ratio. Fast Fourier Transform Photoluminescence measurements were performed on the GaAs layers; the results were correlated with those obtained from the electrical analysis. A comparison of the obtained data with the results of an analogous investigation, previously performed on intrinsically Carbon doped GaAs layers, allowed the following conclusions: a) the GaAs layers exhibit a low content of non-intentional impurities (<1014 cm–3); b) both Zinc and Carbon show a low compensation ratio; c) both Carbon and Zinc doped layers show electrical and optical properties comparable with the state of the art; d) Carbon intrinsic doping appears preferable for low-medium carrier concentrations, while Zinc appears preferable for medium-high carrier concentrations (higher than about 5 × 1017 cm–3). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Applied Surface Science, 2004

Lattice-matched, single and multiple InGaP/GaAs/InGaP quantum wells (QWs) were grown at 600 8C by... more Lattice-matched, single and multiple InGaP/GaAs/InGaP quantum wells (QWs) were grown at 600 8C by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE), with the use of the tertiarybuthylarsine (TBAs) and tertiarybuthylphosphine (TBP) group-V sources. In order to enhance the interface abruptness, different gas switching sequences were exploited during the growth of the interface, and the best results were obtained by inserting a few monolayer-thick GaAsP interlayers (IL), at the direct GaAs-on-InGaP interface. Low-temperature photoluminescence (PL), high resolution X-ray diffraction, transmission electron microscopy and photoreflectance spectroscopy analysis were performed on the grown heterostructures, to correlate the adopted growth sequence with the interface properties and the QW optical transitions.