A.V. Mazanik

Electrical activity of grain boundaries in silicon bicrystals and its modification by hydrogen plasma treatment

Electrical activity of grain boundaries (GBs) and its transformation under the influence of low-energy hydrogen plasma treatment in p-type silicon bicrystalline samples cut from EFG silicon polycrystals were investigated. Comprehensive studies have enabled one to investigate the electrical activity of GBs relative to the minority (MIC) and majority (MAC) carriers and to demonstrate the possibility of controlling this activity by different processing methods. These studies allowed for establishing the correlation between the type, structure and individual electrical activity of GBs and also thermal pre-history of samples. Among the tested modes, hydrogenation was found to be the most radical method of electrical activity modification for all types of GBs. In the process, results on hydrogenation of GBs in EFG silicon crystals depend essentially on three factors: type of GBs, state of ribbons (as-grown or annealed) and concurrence of grain boundary dangling bonds and boron passivation effects.

TRANSFORMATION OF ELECTRICAL ACTIVITY OF EXTENDED DEFECTS IN SILICON POLYCRYSTALS UNDER ANNEALING AND HYDROGEN PLASMA TREATMENT

A possibility to control the electrical activity of extended defects (grain boundaries, dislocations) under annealing and hydrogen plasma treatment by different regimes of silicon ribbons grown with the edge-defined film-fed growth technique was studied. It is shown that the results of hydrogenation of grain boundaries (GBs) significantly depend on two factors: the type of GBs (deviated or general) and the state of ribbons (as-grown or annealed). Heat treatment of polysilicon in different ambients results in a considerable decrease of the electrical activity of dislocation, and special and weakly-deviated GBs too. On the contrary, the activity of general and highly-deviated GBs is enhanced after annealing. Our investigation has revealed that the electrical activity of general GBs is defined significantly by the cooling rate after annealing.

Influence of wide band gap oxide substrates on the photoelectrochemical properties and structural disorder of CdS nanoparticles grown by the successive ionic layer adsorption and reaction (SILAR) method

Summary The photoelectrochemical properties of nanoheterostructures based on the wide band gap oxide substrates (ZnO, TiO2, In2O3) and CdS nanoparticles deposited by the successive ionic layer adsorption and reaction (SILAR) method have been studied as a function of the CdS deposition cycle number (N). The incident photon-to-current conversion efficiency (IPCE) passes through a maximum with the increase of N, which is ascribed to the competition between the increase in optical absorption and photocarrier recombination. The maximal IPCE values for the In2O3/CdS and ZnO/CdS heterostructures are attained at N ≈ 20, whereas for TiO2/CdS, the appropriate N value is an order of magnitude higher. The photocurrent and Raman spectroscopy studies of CdS nanoparticles revealed the occurrence of the quantum confinement effect, demonstrating the most rapid weakening with the increase of N in ZnO/CdS heterostructures. The structural disorder of CdS nanoparticles was characterized by the Urbach energy (E U), spectral width of the CdS longitudinal optical (LO) phonon band and the relative intensity of the surface optical (SO) phonon band in the Raman spectra. Maximal values of E U (100–120 meV) correspond to СdS nanoparticles on a In2O3 surface, correlating with the fact that the CdS LO band spectral width and intensity ratio for the CdS SO and LO bands are maximal for In2O3/CdS films. A notable variation in the degree of disorder of CdS nanoparticles is observed only in the initial stages of CdS growth (several tens of deposition cycles), indicating the preservation of the nanocrystalline state of CdS over a wide range of SILAR cycles.

Photoelectrochemical and Raman characterization of In2O3 mesoporous films sensitized by CdS nanoparticles.

Summary The method of successive ion layer adsorption and reaction was applied for the deposition of CdS nanoparticles onto a mesoporous In2O3 substrate. The filling of the nanopores in In2O3 films with CdS particles mainly occurs during the first 30 cycles of the SILAR deposition. The surface modification of In2O3 with CdS nanoparticles leads to the spectral sensitization of photoelectrochemical processes that manifests itself in a red shift of the long-wavelength edge in the photocurrent spectrum by 100–150 nm. Quantum-confinement effects lead to an increase of the bandgap from 2.49 to 2.68 eV when decreasing the number of SILAR cycles from 30 to 10. The spectral shift and the widening of the Raman line belonging to CdS evidences the lattice stress on the CdS/In2O3 interfaces and confirms the formation of a close contact between the nanoparticles.

Giant Incident Photon‐to‐Current Conversion with Photoconductivity Gain on Nanostructured Bismuth Oxysulfide Photoelectrodes under Visible‐Light Illumination

Nanostructured layered bismuth oxysulfide films synthesized by chemical bath deposition reveal a giant incident photon-to-current conversion efficiency (IPCE). This study shows that surprisingly for the cathodic photocurrent in the photoreduction process, the IPCE reaches ≈2500% in aqueous solutions containing [Fe(CN)6 ]3- . The giant IPCE is observed starting from a certain minimal oxidizer concentration (c > 10-3 m for [Fe(CN)6 ]3- ) and decreases nonlinearly with an increase of illumination intensity. Giant IPCE is determined by the decrease in resistivity of the bismuth oxysulfide film under illumination with photoconductivity gain, which provides the possibility of charge carriers from an external circuit to participate in the photoreduction process. Giant IPCE is observed not only in [Fe(CN)6 ]3- solutions, but also in electrolytes containing other photoelectron acceptors: Fe3+ , I3- , quinone, H2 O2 . In all, solution-processed layered bismuth oxysulfide films offer large-area coverage, nontoxicity, low cost, and compatibility with a wide range of substrates. Abnormally high photoelectrochemical activity, as well as a band gap energy value favorable for efficient conversion of solar light (1.38 eV, direct optical transitions), proves the potential of bismuth oxysulfide photoelectrodes for a new generation of high-performance photoconverters.

Formation of the buried insulating SixNy layer in the region of radiation defects created by hydrogen implantation in silicon wafer

The radiation defects in 10 Ω⋅cm p-type and 4.5 Ω⋅cm n-type Cz Si were created at depth of 0.8-1 µm using 100 keV 2⋅1016 at/cm2 hydrogen implantation at room temperature. Then the introduction of nitrogen into silicon and its diffusion were carried out at different thermodynamic conditions. Finally, the samples were vacuum annealed at 800 oС during 2 h. The state of sample surfaces was studied by SEM. The depth and thickness of SixNy layer and also defect numbers were estimated by RBS method in the channeling mode. The electrical properties of the obtained structures were characterized by the transversal conductance measurements with the keep of a standard LCR-meter at a frequency of 1 MHz using the two-probe method. Our experiments have shown that the above-described method enables one to form the buried SiхNy layer with dielectric properties and the number of defects and nitrogen atoms on the silicon surface and in the near-surface region are comparable with those for the initial silicon wafers.

Gettering of Oxygen onto Buried Defect Layer in Hydrogen Implanted Silicon Wafers after Low Temperature Surface Saturation by Oxygen and Vacuum Annealing

The 10 Ω⋅cm boron-doped Cz-Si wafers were implanted by 100 keV H + and He ions with doses (2.0 ÷4.0)⋅10 cm and then subjected to low-temperature saturation by oxygen from DC plasma source and annealing in vacuum at 250 C or 500 C for 4 h. SIMS measurements have shown that oxygen plasma pre-treatment of H -implanted silicon wafers and their subsequent vacuum low-temperature annealing result in gettering of oxygen from the surface onto the buried defect layer. Measurements in the scanning electron beam induced volt age mode of SEM have exhibited the formation of inhomogeneously distributed contrast, induced by the presence of the buried electrically active extended defects at depths close to a maximal oxygen content. This contrast represents a system of dark spots with a more or less ordered structure the dimensions of that are dependent on the dose of H + pre-implantation.

Electrical characterization of interfaces in unitype directly bonded silicon wafers

Abstract The effect of processing technology and oxygen contamination on the electrical characteristics of the interface of unitype directly bonded Si wafers is investigated. A study on p–p and n–n bicrystals bonded after joining in air or deionized water shows that the interface activity is defined by a contamination level of oxygen and acceptor-like impurities (probably aluminum). The activity of oxygen-free interface in the bicrystals manufactured by joining and annealing of ion-etched wafers in vacuum depends mainly on mismatching of the bonded wafer crystal lattices. The properties of bicrystals with a buried oxide layer specially grown before bonding are strongly dependent both on the homogeneity of SiO 2 and contamination of SiO 2 /Si interface by aluminum.

Synthesis and properties of doped ZnO ceramics

In our work, we studied zinc oxide ceramic samples doped with aluminum and gallium. Structure peculiarities of ceramics depending on their synthesis regime were investigated by the SEM, EDX, XRD, and Raman spectroscopy methods. It was demonstrated that at some technological conditions the formation of indesirable phases of zinc aluminate or gallate may occur preventing an uniform material doping and reducing quality of samples. Single-phase ZnO ceramics were produced when the nanostructured alumina powders were used as a dopant source. The correlations between the synthesis regimes of ZnO ceramics and their electrophysical parameters essential for thermoelectric figure-of-merit (electrical conductivity and Seebeck coefficient) have been established. The best electrophysical characteristics were obtained when the nanostructured alumina produced by combustion in isopropyl alcohol was used as a dopant. Conductivity and Seebeck coefficient of such ceramics are equal to 3·10 S/m and -0.27 mV/K, respectively, corresponding to the power factor of 2.2·10 W/(m·K). Streszczenie. W naszej pracy zbadaliśmy próbki ceramiki tlenku cynku domieszkowanej aluminium oraz galem. Specyfikę struktury ceramiki zależącą od warunków syntezy zbadano metodami SEM, EDX, XRD oraz spektroskopią Ramana. Zaprezentowano, że dla niektórych warunków technologicznych tworzą się niepożądane fazy glinianu cynku lub galusanu zapobiegając jednolitemu domieszkowaniu materiału oraz zmniejszając jakość próbek. Jednofazowa ceramika ZnO została uzyskana w czasie, gdy nanostrukturalny proszek tlenku aluminium był używany jako źródło domieszki. Określono powiązania pomiędzy warunkami otrzymywania ceramiki ZnO oraz jej elektro-fizycznymi parametrami niezbędnymi do termoelektrycznego współczynnika jakości (przewodnictwo elektryczne oraz współczynnik Seebeck`a). Najlepsze elektrofizyczne charakterystyki otrzymano, gdy używano jako domieszkę nanostrukturalny tlenek aluminium produkowany poprzez spalanie w alkoholu izopropylowym. Przewodność oraz współczynnik Seebeck`a tego typu ceramik wynosi odpowiednio 3·10 S/m oraz -0.27 mV/K, co odpowiada współczynnikowi mocy równemu 2.2·10 W/(m·K). (Synteza i właściwości domieszkowanej ceramiki ZnO).

Raman Scattering and Carrier Diffusion Study in Heavily Co- doped 6H-SiC Layers

Thick 6H-SiC epilayers were grown using the fast sublimation method on low-off-axis substrates. They were co-doped with N and B impurities of ≈1019 cm−3 and (41016–51018) cm−3 concentration, respectively. The epilayers exhibited donor-acceptor pair (DAP) photoluminescence. The micro-Raman spectroscopic study exposed a compensated n-6H-SiC epilayer of common quality with some 3C-SiC inclusions. The compensation ratio of B through 200 μm thick epilayer varied in 20-30% range. The free carrier diffusivity was studied by transient grating technique at high injection level. The determined ambipolar diffusion coefficient at RT was found to decrease from 1.15 cm2/s to virtually 0 cm2/s with boron concentration increasing by two orders.