Papers by Author: I.V. Antonova

Abstract: A physical picture of swift heavy ion irradiation effects on ensembles of silicon nanocrystallites (NCs) embedded in a dielectric SiO₂ matrix is given following our study of the experimental investigation of structural, electrical and photoluminescence properties of that system We found that ion irradiation can drastically change the structure of the layer by forming an ordered NC chains along the ion tracks in the 400-1000 nm thick layer. The ion energy and dose are then the main tools for functionalization of our system, from changing the size and the concentration of the NCs, to managing the optical and electrical properties.

Abstract: The set of quantum confinement levels in SiGe quantum wells (QW) was observed in the temperature range from 80 to 300 K by means of charge deep-level transient spectroscopy (Q-DLTS) and transport measurements. These observations proved possible due to a passivation of structure surface with organic monolayer deposition. Si/SiGe/Si structures with different Ge contents in SiGe layer were studied. The confined levels in passivated structures became apparent through DLTS measurements as various activation energies in temperature dependence of the rate of carrier emission from QW. It was found that the recharging of SiGe QWs and carrier emission accomplish due to thermo-stimulated tunneling. The steps in the current-voltage characteristics originated from direct tunneling via the confined states were found to determine the current flow at high fields.

Abstract: In the present paper we discuss effects due to high-energy ion bombardment of SiO2 layers with embedded Si nanocrystals (NCs), such as the formation of new Si NCs in such layers, amorphization of previously existing NCs, modification of NC size distribution, and modification of optical and electrical properties of NCs. These effects are identified as resulting from anisotropic strain - anisotropic heating in NCs-SiO2 layers under ion irradiation.

Abstract: Samples with layer of silicon nanocrystals embedded in SiO2 (the single phase Si content in oxide ranged between 5 and 92 volume %) were subjected to high energy ion implantation. Implantation-induced modifications of SiO2-ncSi properties discussed in this paper include a shift of the major ncSi-related photoluminescence peak and intensification of the high-photon energy peaks, that accompany the change in amount and type of the charge trapped on the nanocrystals. A unified model is suggested for all these phenomena.

Abstract: Fast neutron irradiations on pre-treated Cz-grown silicon were carried out. The pretreatments involved thermal anneals at 450 oC and 650 oC under high hydrostatic pressure. We mainly examined, by means of IR spectroscopy, the effect of pre-treatments on the production of the oxygen-vacancy (VO) pair. The amplitude of the VO band was found independent on the 450 oC treatment although the amplitudes of the TDs bands were reduced. On the other hand, the amplitude of the VO band was found lower in the samples treated at 650 oC, indicating an influence on the production of the oxygen-vacancy defects. The results are discussed and explanations are suggested concerning possible interactions between thermal and radiation defects.

Abstract: The electrical properties of structures included 1-octadecene (CnH2n, n=18) monolayers deposed onto the oxide-free silicon surface or Si/SiGe/Si layers were analyzed as a function of surface pretreatment (hydrogen- or iodine-terminated silicon surface) and layer deposition regime (thermal- or photo-activated process). Two types of traps (for electrons and holes) were found at the interface between the monolayers and substrate. The density of traps was shown to depend on the, H- or I-termination of the silicon surface, the illumination intensity and deposition time during photo-activated deposition, and the temperature of thermal-activated deposition. The optimal regimes can be chosen for minimization of the surface charge in the structures covered with 1- octadecene monolayers, which provides a high conductivity of thin near-surface layers.

Abstract: Transformations of the SiGe/Si superlattice structures, either annealed at high pressure, or irradiated by high energy ions and subjected to post-implantation annealing, were studied and compared. Both types of treatments were found to lead to the formation of recharged defects clusters, resulting in the appearance of peaks on C-V characteristics, shrinkage of Ge profiles registered by SIMS technique after annealing, and disappearance of peaks in the free carrier profiles. The effects were more pronounced in the case of high energy ion implantation. The results are explained by the vacancy - assisted precipitation of Ge in SiGe layers.

Abstract: Electrical transport and traps in vertical SiGe/Si QW structures of low background doping level are studied in the presented report. Temperature activation of holes from the quantum well was found to determine the vertical current through Si/SiGe/Si structures at T > 160 K. At lower temperatures (T < 130 K), the current mechanism is attributed to a thermally activated tunneling of holes from quantum well. Deep traps are observed in the Si/SiGe/Si structures in high concentration (1011 – 1012 cm-2). Traps are most likely assistance in the current in the vertical Si/SiGe/Si structures as recombination centers near the QW.