Silicon-rich Regions Research Articles

Suppression of Antiferromagnetism by Kondo Effect and Quantum Critical Behavior in CeCoGe3-xSix(0≤x≤3)

Several pseudoternary compounds of the CeCoGe 3- x Si x system were studied by magnetic-susceptibility, electrical-resistivity and specific-heat measurements. Substitution of silicon for germanium generates the normal chemical pressure and enhances the exchange interaction. The antiferromagnetism in CeCoGe 3 is ultimately suppressed around x =1.2 by the enhanced Kondo effect. Non-Fermi liquid-like behavior has been observed around the critical concentration and an intermediate-valence regime with a very high Kondo temperature of the order of 900 K is followed farther on in the silicon rich region.

Physico-chemical and MAS NMR characterization of mesoporous SAPOs

Mesoporous SAPOs (average pore radius ∼30 Å) have been synthesized using organized micellar arrays of templates. The synthesized SAPOs have been characterized by XRD, TEM, TGA, sorption and MAS NMR techniques. There is no evidence of Si–O–P linkages in these materials. The distribution of silicon around Al ions was studied by calcination at higher temperatures. The possibility of synthesizing mesoporous SAPOs with silicon rich regions, possessing lesser acidity than the zeolites, will open up new avenues for their technical applications.

Nanodispersed Cr xSi 1−x thin films: transport properties and thermoelectric application

The electrical resistivity and thermopower of heterogeneous Cr x Si 1− x thin films have been investigated in terms of their dependence on the degree of crystallization arising from a post-deposition annealing treatment. The films were prepared by physical vapour deposition within the silicon rich region 0.2< x<0.3. At high annealing temperatures the films investigated were found to be two-component systems consisting of CrSi 2 and Si crystallites. The transport behaviour is discussed on the basis of the X-ray structural analysis results. The thermoelectric efficiency of the deposited films can be influenced by the heat treatment conditions. Using a combination of annealed binary CrSi and ternary CrSiN thin films it is possible to prepare thermocouples for application at elevated temperatures.

Electronic properties of hydrogenated amorphous silicon-germanium alloys

The electronic properties of some binary hydrogenated amorphous silicon-germanium alloys a-SixGe1-x: H in the silicon rich region (x > 0.6) are investigated. Experimental evidence is presented of photo-induced effects similar to those described in a-Si:H (Staebler-Wronski effect). The electronic properties are then studied from the dual point of view of the germanium content dependence and of the photo and thermal histories of the films. The dark conductivity changes between the annealed state and the light-soaked state are interpreted in terms of the variation of the temperature coefficient of the Fermi level. The photoconductivity efficiency is shown to remain close to that of a-Si:H for 1 > x ≽ 0.9 and to strongly decrease when the germanium content is further increased : the photoresponse of the Si0.62Ge 0.38 alloy is 104 times smaller than that of a-Si:H. This deterioration of the photoconductive properties is explained in terms of the increase of the density of gap states following Ge substitution. This conclusion is based on the study of the width of the exponential absorption edge and on the results of photoconductivity time response studies. The latter data are interpreted by means of the model of Rose of trapping and recombination kinetics and it is found that for x ≃ 0.6 the density of states at 0.4-0.5 eV below the mobility edge is 7 x 10 17 eV-1 cm-3 as compared to 2.4 x 1016 eV-1 cm-3 for x = 0.97.

Auger electron spectroscopy analysis of the contact reaction of PtSi codeposited films and silicon

Codeposited alloy films of PtSi on silicon, proposed earlier for the formation of shallow Schottky contacts, were studied by Auger electron spectroscopy. The contact depth after annealing was found to be larger than expected. An accumulation of silicon and a depletion of platinum in the outer 200–300 Å of the film was also observed. Analysis of the line shape for the Auger transitions leads to the conclusion that the outer silicon-rich region consists of a mixture of PtSi and elemental silicon, probably as a result of silicon out-diffusion.

Direct Observation of the Growth of Sputtered Gold Films on (111) Silicon Substrates

The study of in situ Ion beam sputtering of gold on substrates of single crystal silicon using well controlled ultrahigh vacuum deposition system shows that substrate/overgrowth interactions involving alloying and interdiffusion greatly influence the growth and structure of sputtered thin gold films.Gold was sputter deposited on substrates of single crystal at temperatures ranging from 23°C to 500°C and a deposition rate of 15Å/min in vacuum of 2x10-8 torr. The growth and structure of the deposits shows large differences in two substrate temperature regions, the low temperature regions below 200°C and the high temperature regions above 200°C. At low substrate temperatures below 200°C, an amorphous film is first formed as shown in Figure la and followed by the growth of two dimensional polycrystalline gold islands on the newly formed amorphous layer as shown in Figure lb. At high substrate temperatures above 200°C, a liquid alloy of Au-Si and polycrystalline silicon rich regions are formed on the substrate as shown in Figure 2a. The liquid alloy of Au-Si and polycrystalline silicon rich regions are phase transformed to the polycrystalline gold and silicon rich regions during cooling to room temperature as shown in Figure 2b.

Line-shape extraction analysis of silicon oxide layers on silicon by channelling effect measurements

Abstract A technique of line-shape extraction has been developed and applied to find the number of Si atoms and O atoms per square centimeter of anodically grown and thermally oxidized silicon oxide layers. Back-scattering and channelling effect measurements with 0.3-2.0 MeV 4He+ ions were used. The thicknesses of the silicon oxide investigated ranged from native oxide thickness to 1500 A. For all thicknesses the composition was found to be silicon-rich, with the number of Si atoms per square centimeter equal to one-half the number of oxygen atoms per square centimeter plus (0.8-1) × 1016 Si/cm2. We propose that the oxide layer is stoichiometric SiO2 with a silicon-rich transition region between the oxide layer and the crystal substrate. The presence of such a transition region at the interface should be considered when evaluating the composition of dielectric layers on semiconductors.