B. R. Chakraborty

Gd2O3, Ga2O3(Gd2O3), Y2O3, and Ga2O3, as high-k gate dielectrics on SiGe: A comparative study

In this paper we report a comparative study of the electrical properties of some oxides e.g. Gd 2 O 3 , Ga 2 O 3 (Gd 2 O 3 ), Y 2 O 3 and Ga 2 O 3 as gate dielectric for strained Si 0.74 Ge 0.26 MOS devices. The deposited films have been characterized using EDAX, SIMS and ellipsometry. The Au / oxide / SiGe MIS structures using these insulators were examined using I-V, C-V and G-V techniques. Though Gd 2 O 3 and Y 2 O 3 showed highest resistivity and breakdown strength, Ga 2 O 3 (Gd 2 O 3 ) was found to be most effective for surface passivation of SiGe giving lowest interface state density while pure Ga 2 O 3 was incapable of passivating SiGe surface.

DC Conductivity in Barium Hexaferrites Doped with Bismuth Oxide

Barium hexaferrites of compositions BaO(6- x)Fe2O3 xBi2O3 with 0 \leqslantx \leqslant0.4 have been synthesized by the ceramic calcination route. The bismuth substituted hexaferrites exhibit dc electrical conductivities more than two orders of magnitude higher than the pure ones. This is believed to arise due to an increase in the concentration of Fe2+ ions as a result of the presence of Bi5+ ions in these compounds. The dc conductivity at temperatures higher than 250 K can be explained on the basis of a non-adiabatic hopping model of small polarons, the variable valence iron ions forming the polaronic sites. At temperatures lower than 220 K a variable range hopping mechanism appears to control the conductivity.

Formation of cobalt silicides as a buried layer in silicon using high energy heavy ion irradiation

A multilayer heterostructure of Si(50 nm)/Co(50 nm)/Si(50 nm)/Si 100 was prepared by an e-beam evaporation technique under UHV conditions and it was then subjected to irradiation by 120 MeV Au+ ions with fluence varying between 1013 and 1014 ions cm−2. No external thermal treatments were used. Secondary ion mass spectrometry was used in the depth profile mode, which indicated a monotonic increase in the mixing width with fluence at the first interface of Si/Co. Depth profile analysis suggested major changes in the preferential sputtering rates of Co at the interface indicating formation of silicides. Further investigation by x-ray diffraction confirmed the formation of different phases of cobalt silicides, Co2Si, CoSi and CoSi2, as a buried layer, while the Raman spectroscopy showed broad peaks near 325 and 725 cm−1, which are characteristic of the CoSi2 phase. The above work suggests that swift heavy ion irradiation can be advantageously used for interconnect related buried layer silicide formation at room temperature avoiding thermal annealing.

Quantum size effect in silicon nanocrystals prepared by dc magnetron sputtering

Silicon nanocrystals have been prepared in thin-film form by a dc magnetron sputtering technique. The optical transmission, optical absorption, Raman effect and photoluminescence of the nanocrystals have been studied. The observed blueshift of the band gap due to a reduction in the crystallite size is correlated with the transmission electron microscopy observation. Raman spectra indicated the presence of a TO mode which showed redshift with the decrease in the size of the nanocrystallites.

SIMS characterization of GaAs MIS devices at the interface

Abstract We report here the improvements in the electrical characteristics of Au/Si x N y /n-GaAs structures with NH 3 plasma treatment of GaAs prior to PECVD of a Si x N y dielectric film followed by annealing at 450 °C. These structures were characterized by secondary ion mass spectrometry (SIMS) depth profiling. The depth profiles of the three samples discussed in the present report show that the unpassivated sample has a broad interface consisting of both Ga–O and As–O species. After passivation, the interface becomes quite sharp, but the presence of both the oxides is still observed. However, after annealing, although the interface thickness increases marginally due to diffusion further into the substrate, it is observed that the interface becomes N-rich, which has also been supported by preliminary FTIR data. Looking at the electrical properties, it is seen that the unpassivated sample gives poor device characteristics which are attributed to the presence of wide oxide layers as shown by the SIMS data and consequently Fermi level pinning due to high interface state density, while the NH 3 passivated samples show better device characteristics. This is attributed to the fact that the interface state density reduces considerably as the interface thickness reduces. Post-deposition annealing showed marked improvement in device characteristics with decrease in frequency dispersion, conductance and hence interface state density as revealed from C – V and G – V measurements.

Mixed valency character of bismuth in ferrite lattices

Abstracts are not published in this journal

Deep-level core-electron loss studies on silicon surface

Abstract Slow-electron energy-loss spectroscopic studies of the deep-core levels of the silicon (111) surface, in the reflection mode, are reported here. The 1s (K-shell) core-electron loss energy as observed for a silicon single crystal on the (111) face is 1842 eV. To support the above results the core loss energies of 2s and 2p electrons and the volume and surface plasmon losses on silicon are also reported.

Quantification of the mixing effect in silicon–manganese thin films by swift heavy ion irradiation

Swift heavy ion induced mixing is reported in a-Si/Mn/a-Si thin films on a silicon wafer, when irradiated by 120 MeV Au ions at three different fluences of 1 × 1013, 3 × 1013 and 1 × 1014 ions cm−2. The samples were characterized before (pristine) and after irradiation using secondary ion mass spectroscopy (SIMS) and Rutherford backscattering spectroscopy (RBS). Atomic force microscopy of the samples was used to determine the surface roughness contribution to RBS and SIMS profiles. Depth profiles showed distinct changes in the interface region and it was observed that interface mixing increased linearly with the increase in the ion fluence. The mixing rate was estimated to be ~1000 nm4. The mixing effect is explained in the framework of the thermal spike model. The track radius and duration of the transient melt phase have been theoretically calculated for this system to estimate the diffusivity during the transient melt stage at the interface.

Study of oxidation and silicidation of Ta by electron impact autoionization process

Abstract Electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES) have been used to study the electron impact autoionization process in Ta 2 O 5 and TaSi 2 . The role of d electrons in Ta during chemical bonding with oxygen and silicon is observed. A comparative study of low energy AES (0–50 eV) and EELS in TaSi 2 with that of Ta 2 O 5 and pure Ta shows some definite change in the p-d and f-d quasi-atomic transitions. The decrease in intensity of the 49.0 eV peak in EELS and the 44.5 eV peak in AES spectra related to the autoionization process in the case of TaSi 2 , as compared to Ta, suggests a dip in the empty density of states (DOS) of Ta due to its dominantly covalent type of bonding caused by sharing the d electrons with the Si p electrons. But Ta 2 O 5 shows almost no change in the intensity of similar transitions in EELS and AES suggesting no dip in the DOS above the Fermi level. The multiplet splitting of Auger NOO transition at 167 and 172 eV, caused by the interaction between the doubly ionized p level and the unpaired d electrons, is observed to decrease in the case of Ta 2 O 5 due to depletion in Ta d-band occupancy and is associated with a dominantly ionic type of bonding. This decrease in d-band population in Ta 2 O 5 is supplemented by a chemical shift of 2 eV in the NNN (178 eV) transition due to charge transfer. It has been demonstrated here that conventional electron spectroscopies like AES and EELS can be used to probe near-Fermi-level features like the d-band occupancy of transition metals.

Electron‐stimulated desorption of fluorine from barium fluoride films deposited on silicon substrates

The desorption of fluorine from barium fluoride thin films deposited on silicon substrate has been observed due to the incidence of electron beam during Auger electron spectroscopic (AES) studies. Slow electron energy loss spectroscopy (SEELS) has been employed to observe changes in core levels and color center formation. The desorption cross section for fluorine and the critical electron beam dose necessary to initiate electron‐stimulated desorption have been estimated. The results are envisaged to provide information to investigators performing AES on such materials to choose parameters so as to eliminate or reduce beam damages. Since the desorption of fluorine results in metalliclike barium on the surface, it can also be a technique to deposit clean Ba layers on cathode materials to achieve work‐function reduction.