Papers by Author: V.P. Popov

Abstract: Properties of Si/buried oxide (BOX) systems with bonded interface in silicon-on-insulator (SOI) wafers were studied in this paper. Results show impact of the starting Si material - Czochralski (Cz) or float-zone (Fz) grown silicon on the electron mobility (μ_e) and BOX charge behavior in ultrathin SOI layers. In particular, there were found: 1) the μ_e ~ N_e^-0.3 dependencies at the electron density N_e in the range of 4х (10¹¹-10¹²) cm^-2 in accumulation Cz-SOI layers with the μ_e degradation when Si thickness decreases from 20 to 9 nm, and 2) the ~ N_e^-0.6 behavior of mobility with no degradation in Fz-SOI layers. Raman spectroscopy shows the structural modification of Cz-SOI layers. An origin of degradation of the electrical and structural properties for ultrathin SOI layer is discussed.

Abstract: In the present study, the pursued purposes were: (i) monitoring the electrical properties of silicon-on-insulator nanowires (SOI NWs), (ii) determination of surface treatments suitable for obtaining reproducible states on the surface of SOI NWs after their long-term storage, and (iii) identification of surface treatments suitable for regenerating the NW surface after protein (bovine serum albumin molecules) detection. It is shown that, during storage, with the passage of time a negative effective charge was accumulated on the surface of n-SOI NWs up to surface density Q_eff = (2-4)х10¹² cm^-2, while the interface states at the NW/SiO₂ interface underwent relatively slow depassivation. Treatments in H₂O₂ with subsequent treatments in HF can be used for removing organic contaminations from the NW surface and for regenerating the initial working state of SOI NWs after protein detection.

Abstract: Mobility degradation during gate length scaling is a well established experimental fact, which is confirmed also by Monte –Carlo simulation. We have analyzed the physical reason for this degradation using experimental and modeling data obtained in classic drift-diffusional approximation with electric field dependences of electron mobility. We have shown that this dependence is a main reason for mobility degradation in nanoscale FETs, which means also that the same reason will limit the drain current in future post-silicon CMOS generation with new materials like narrow band III/V compounds or graphene with the highest carrier velocity near 108 cm/s.

Abstract: Graphitic-diamond heterostructure may be very helpful not only for high frequency or power devices but also for new generation of electronic devices like single electron transistors or quantum computers operated at room temperature. The goal of our work was a formation of nanothin amorphous carbon or graphite layers with sp3 or sp2 hybridization inside the nitrogen doped synthetic monocristalline diamond by high dose hydrogen implantation. It was found that there is a “critical” dose of 50 keV hydrogen molecular ions equal to 4x1016 cm-2 above which an irreversible drop of the sheet resistivity in implanted layer occurs after annealing above 1000 oC. The nature of this conductivity was investigated and it was shown that variable range hopping mechanism of 3D conductivity dominates in investigated temperature interval. Four times higher value for the onset of this conductivity in comparison with “critical” dose for graphitization is explained by interaction of implantation induced defects with nitrogen atoms and surface defects.

Abstract: The properties of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator (SOI) structures are studied. It is shown that no germanium nanocrystals are formed in the buried SiO2 layer of the SOI structure as a result of annealing at the temperature of 1100° C. The implanted Ge atoms segregate at the Si/SiO2 bonding interface. In this case, Ge atoms are found at sites that are coherent with the lattice of the top silicon layer. It is found that the slope of the drain–gate characteristics of the back metal-oxide-semiconductor (MOS) transistors, prepared in the Ge+ ion implanted structures, increases. This effect is attributed to the grown hole mobility due to the contribution of an intermediate germanium layer formed at the Si/SiO2 interface.

Abstract: The behavior of Sb and In atoms embedded into silicon-on-insulator structure (SOI) near the bonding interface was investigated as a function of annealing temperature. Two kinds of the ionimplanted SOI structures were prepared. First kind of the structures contained the buried SiO2 layer implanted with In+ and Sb+ ions near the top Si/SiO2 interface. In second kind, the ion-implanted regions were placed on each side of the bonding interface: Sb+ ions were implanted into Si film; In+ ions were implanted into SiO2 layer. Rutherford backscattering spectrometry (RBS) and crosssectional high-resolution electron microscopy (XTEM) were employed to study the properties of the prepared structures. The formation of InSb nanocrystals was observed within the SiO2 bulk from first kind of the SOI structures as annealing temperature increased to 1100o C. In the case of the double side implanted SOI structures, an increase in annealing temperature to 1100o C was accompanied by the up-hill diffusion of In atoms from the SiO2 bulk toward the bonding interface and by the endotaxial growth of InSb nanocrystals on the top Si/SiO2 interface. It was concluded from the experimental results that Sb atoms were the nucleation centers of InSb phase.

Abstract: Cavity effect on the room-temperature (RT) photoluminescence (PL) from emitting centers in the top silicon layer of silicon-on-insulator (SOI) structure has been studied. The lightemitting centers were produced by the implantation of H+ ions and subsequent annealing at the temperatures Ta = 450-1000 oC for 5 h in an Ar ambient under pressure P = 1 - 1.2×104 bar. It has been obtained that annealing under hydrostatic pressure higher than 6 kbar prevented the outdiffusion of hydrogen in the form of gas bubbles, which took place after annealing at Ta≥600 oC under atmospheric conditions. Absence of micro-pores and gas bubbles in the top surface region creates the conditions to retain the mirror quality of the SOI/air interface. A wavelength-selective effect of the formed cavity on visible PL has been observed from the H+ ion implanted SOI structures annealed under pressure of 12 kbar. The cavity enhancement of PL emission for 23-40 times has been found at the wavelength of 515 and 560 nm.

Abstract: Electro-physical properties of metal-oxide-silicon (MOS) structures and MOS transistors, prepared in the top silicon layer of silicon-on-insulator (SOI) structures containing Ge nanocrystals in the buried SiO2 layers, have been studied. It was obtained that carrier accumulation in MOS structures depend on the direction of built-in electrical field in MOS structures. Accumulation of the excess negative charges in the case of p-channel transistors is associated with electron trapping on Ge nanocrystals synthesized in the buried dielectric. In the case of n-channel transistor, positive charge related to the Si/SiO2 interface or to the charged oxide is accumulated. The Ge atoms diffused to the SiO2/Si interface can stimulate the formation of the excess positive charge.