In this paper, we investigate the influence of postgrowth thermal treatment on the structural qua... more In this paper, we investigate the influence of postgrowth thermal treatment on the structural quality and surface morphology of crystalline Y 2 O 3 films prepared by molecular beam epitaxy (MBE) on (001) Si substrates. As-grown films are characterized by a relatively thick interfacial layer, which develops during growth. In situ annealing under ultrahigh vacuum results in the desorption of this layer and the formation of very sharp Y 2 O 3 /Si interfaces. However, in situ annealing degrades the insulating properties of the films. Ex situ annealing in O 2 or N 2 atmosphere causes the detachment of the film from the Si substrate, due to the development of large compressive strain as a result of the large difference between the thermal expansion coefficients of Y 2 O 3 and Si. This effect is further studied by atomic force microscopy (AFM) measurements and subsequent surface analysis, which showed the formation of an isotopically organized structure. The effect was absent in amorphous films grown at low temperatures.
. Trapping levels which govern the vertical transport in nc-SirCaF multi-quantum wells were inves... more . Trapping levels which govern the vertical transport in nc-SirCaF multi-quantum wells were investigated using two different 2 n Ž . Ž . Ž . techniques: a the temperature dependence of the dark current and b the thermally stimulated depolarization current technique TSDC . Measurements by the first technique showed that the conduction mechanism was thermally activated above 200 K with activation energies of 0.35-0.7 eV. These activation energies were found to increase with increasing electric field. TSDC measurements showed also the existence of at least one broad peak above 200 K with estimated activation energies in the range of 0.4-0.45 eV. Analysis of the peak by the fractional heating method showed a continuous distribution of defect states from 0.3 to 0.83 eV. q
In this work we examine the influence of thermal oxidation on the electrical characteristics of u... more In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si 0.78 Ge 0.22 substrates under moderate to high thermal budget conditions in N 2 O ambient at 800°C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si 0.78 Ge 0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si 0.78 Ge 0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO 2 -strained silicon interface and the rear strained silicon-Si 0.78 Ge 0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration-as a result of the thermal treatment-to the interfacial properties of the structure is discussed.
Proceedings of the 7th Conference on Semi-insulating III-V Materials,, 1992
Deep states in undoped semi-insulating GaAs with low carbon content were investigated by PICTS an... more Deep states in undoped semi-insulating GaAs with low carbon content were investigated by PICTS and Photo-DLTS. Hall and Photo-Hall measurements proved that peaks observed in Photo-DLTS spectra are due to the electron emission from deep donor states. Other peaks obtained in PICTS spectra were attributed to the hole emission from acceptor states with the apparent energy levels Epa= 0.18, 0.19, 0.21, 0.5 eV. A minimal value of their total concentration except of 0.5 eV level was estimated at about lx1015 ~m -~. The peak of 0.5 eV level with dominant amplitude in detected spectra correlates with the hole emission from EL2+/++ double donor state. The 0.19 and 0.21 levels are most probably related to the double acceptor GaAs antisite. defect.
This work presents an alternative method for the formation of the top oxide in oxide-nitride-oxid... more This work presents an alternative method for the formation of the top oxide in oxide-nitride-oxide structures. The method utilizes low-energy (1 keV) Si ion implantation into thin oxide-nitride stacks, followed by low temperature wet oxidation. Transmission electron microscopy examination clearly indicates the formation of a three-layer structure, verified also by Time-of flight secondary ion mass spectrometry. The electrical characteristics of the oxide-nitride-oxide stacks exhibit strong trapping effects and excellent retention characteristics resulting to a 1.5 V 10-year memory window at 125 o C.
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Papers by V. Ioannou