Applications of amorphous semiconductor materials in electronics

A brief summary of the present state of the art of amorphous semiconductors and their applications in modern electronics is presented in this paper. The recent developments in chalcogenide glass thin film devices and in amorphous silicon electronic devices are reviewed. A potentially interesting application of a-Si(p⁺-n-i) thin film structures as fast non-volatile electronic memory elements is also discussed.     

Separation in solid solutions of Fe-W system

The microstructure of Fe-15 wt% W and Fe-18 wt% W alloys has been studied using methods of transmission electron microscopy and X-ray diffraction. It has been shown that in the region of a solid solution the separation microstructure is formed. During isothermal aging at 600°C the separation microstructure is dissolved and before precipitation of the stable Fe₂W phase an unknown metastable phase is formed and then dissolved. The conclusion has been made that a solid solution region in the Fe-W system is actually the region in which a tendency toward separation takes place.     

Formation of metastable solid solutions in the Pb-Ge system

The formation and decomposition behaviours of metastable solid solutions in liquid-quenched and vapour-quenched Pb-Ge alloys were studied using X-ray diffraction, transmission electron microscopy (TEM), differential thermal analysis (DTA) and resistance measurement techniques. It is shown that the Pb-rich fcc phase can retain upto about 13 at% Ge on liquid-quenching and upto about 5 at% Ge on vapour-quenching. Decomposition of the Pb-rich fcc phase occurs in the temperature range 220 to 300° C and it is a temperature dependent nucleation and growth phenomenon. Upto about 7.5 at% Pb can be retained in Ge-rich compositions in an amorphous Ge matrix on vapour-quenching but there is no detectable solubility of Pb in crystalline Ge retained by liquid-quenching. On heating, the amorphous Ge-Pb films crystallize to a Ge-rich solid solution which decomposes to equilibrium constituents at higher temperatures. Stability of amorphous Ge-Pb films decreases on increasing metal concentration.     

Controlled buckling of semiconductor nanoribbons for stretchable electronics

Control over the composition, shape, spatial location and/or geometrical configuration of semiconductor nanostructures is important for nearly all applications of these materials. Here we report a mechanical strategy for creating certain classes of three-dimensional shapes in nanoribbons that would be difficult to generate in other ways. This approach involves the combined use of lithographically patterned surface chemistry to provide spatial control over adhesion sites, and elastic deformations of a supporting substrate to induce well-controlled local displacements. We show that precisely engineered buckling geometries can be created in nanoribbons of GaAs and Si in this manner and that these configurations can be described quantitatively with analytical models of the mechanics. As one application example, we show that some of these structures provide a route to electronics (and optoelectronics) with extremely high levels of stretchability (up to approximately 100%), compressibility (up to approximately 25%) and bendability (with curvature radius down to approximately 5 mm).     

Synthesis and characterization of semimagnetic semiconductor nanocrystals for spin electronics

The technique of pulsed laser deposition and colloidal chemistry methods have been applied for synthesis of semimagnetic semiconductor Cd_1−xMn_xTe nanocrystals embedded in dielectric matrix. The performed analysis suggests a narrower size distribution for the colloidal nanoparticles. Optical absorption, Faraday rotation and photoluminescence spectroscopy have been used to characterize the grown quantum dot structures. The magneto-optical spectra of the Cd_1−xMn_xTe nanocrystals exhibit peculiarities typical for bulk semimagnetic semiconductors due to the strong spin-exchange interaction between band carriers and magnetic ions and simultaneously manifest some features because of confinement effects in low dimensional structures.     

Kinetics of electron-ion processes in CdTe-based solid solutions in the CdTe-CdI2 system

Single-crystal and polycrystalline CdTe-CdI₂ solid solutions containing 0.016 to 0.350 mol % CdI₂ have been studied using microwave photoconductivity measurements. The results demonstrate that the magnitude of their photoresponse and the shape of the photoresponse decay curve depend on the doping level and the degree of dispersion. The observed effect of doping level on the photogenerated electron decay kinetics in cadmium telluride is interpreted in terms of self-compensation, which leads to redistribution of trap energies. The recombination rate constant for free electrons and holes in CdTe is determined to be (3 ± 1) × 10^?11 cm³/s, independent of the doping level and the degree of dispersion of the samples.     

Decomposition behaviours of dopant-free and doped solid solutions in the TiO2-SnO2 system

Decomposition behaviours, including phase separation by the spinodal mechanism, were investigated for selected compositions ofx = 0.7, 0.5 and 0.3 in Ti _x Sn_1–x O₂ alloy. Inside the coherent spinodal, an equimolar alloy was found to decompose most rapidly at 1100° C and the decomposition rate decreased as the annealing temperature increased. The difference in the rate of decomposition outside the spinodal betweenx = 0.7 andx = 0.3 alloys suggested that the ionic mobility of diffusing tin was much slower than that of titanium in the alloy system. The effect of some dopants on the decomposition rate was also examined. Doping with tungsten or antimony atoms strongly suppressed the phase separation both inside and outside the spinodal, especially resulting in a prolonged stabilization ofx = 0.7 alloy. The role of the dopants in affecting the decomposition rate is discussed in relation to selective substitution of the doping atoms in the tin or titanium sublattice.     

The phase diagram and properties of solid solutions of the ternary sodium-lithium-potassium niobate system

A phase diagram of the (Na,Li,K)NbO₃ ternary system in the NaNbO₃ region was constructed using the experimental X-ray diffraction data. Various physical properties of solid solutions were studied in a broad range of component concentrations. Promising compositions for the high-and medium-frequency piezotransducers are determined.     

Present trends and realisations in readout electronics for semiconductor detectors in high energy physics

Design criteria of signal processors for semiconductor detectors in high energy physics experiments are reviewed.Choice of input active devices of preamplifiers, detector-device capacitive matching, preamplifier configurations, variant and invariant signal processors are discussed.Several examples of processors for microstrip silicon detectors and for silicon detector telescopes, are reviewed with particular emphasis on noise performance and high rate capabilities.     

Smooth growth of organic semiconductor films on graphene for high-efficiency electronics

High-quality thin films of conjugated molecules with smooth interfaces are important to assist the advent of organic electronics. Here, we report on the layer-by-layer growth of the organic semiconductor molecule p-sexiphenyl (6P) on the transparent electrode material graphene. Low energy electron microscopy and micro low energy electron diffraction reveal the morphological and structural evolution of the thin film. The layer-by-layer growth of 6P on graphene proceeds by subsequent adding of {111} layers.     

Thermal conductivity of binary and ternary disordered solid solutions of a titanium-zirconium-hafnium system

Measurements of thermophysical properties of ternary alloys of a Ti-Zr-Hf system are presented. The possibility of generalizing such results and predicting the thermal conductivity of ternary continuous disordered solid solution is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 4, pp. 642–647, October, 1977.     

Synthesis and characterization of vanadium-containing ZrO2 solid solutions pigmenting system from gels

A procedure is reported for the synthesis of vanadium-doped zirconia pigmenting system with different vanadium loadings which permitted their complete formation and further characterization. Monoclinic vanadium-zirconia solid solutions were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate and studied over the range of temperature up to 1300 °C. Succesive steps of the reactions leading to the final monoclinic vanadium-zirconia solid solution phase were investigated by X-ray powder diffraction. It was found that the formation of the monoclinic solid solution took place by a phase transformation from a phase with the structure of tetragonal zirconia. The transformation temperature of metastable tetragonal to monoclinic phase was found to be governed by the nominal vanadium amount. Measurements of lattice parameters of monoclinic vanadium-zirconia solid solutions as a function of the nominal vanadium amount revealed that vanadium was dissolved in the zirconia lattice. Energy dispersive X-ray microanalysis and lattice parameters variation indicates that the maximum amount of vanadium into the monoclinic zirconia lattice was about 5 mol % of vanadium (3.7 wt % as V₂O₅). UV-Vis diffuse reflectance of monoclinic V-ZrO₂ solid solutions indicated that vanadium was dissolved as V⁺⁴ and that the color of vanadium-zirconia yellow pigments was produced by the dissolved vanadium.     

Nucleation of solid solutions crystallizing from aqueous solutions

The study of nucleation and growth mechanisms of salts from aqueous solutions, as a function of supersaturation, is described using both macroscopic and microscopic experiments. In situ observations in a fluid cell in an atomic force microscope (AFM) reveal phenomena not accounted for in standard crystal-growth theories, specifically on the role of the crystal structure of the substrate in controlling spiral growth and two-dimensional nucleation. As a model example, the crystallization of two isostructural salts, BaSO(4) and SrSO(4), is described. The growth of solid-solution crystals is considerably more complex. The supersaturation of a given aqueous solution relative to a solid solution is different with respect to each solid composition, and it leads to the possibility that different compositions can simultaneously grow by different mechanisms on the same crystal face. Oscillatory compositional zoning is another consequence of the interplay between the thermodynamics and the kinetics of nucleation. The factors which control nucleation and growth of the solid solution (Ba,Sr)SO(4) from an aqueous solution are described. The predictions made from the theory are compared with direct observations of crystal growth in an AFM.     

Condensation diagram of and phase changes in thin film solid solutions of the CdSxTe1−x system

A condensation diagram of thin film solid solutions of the CdS_xTe_1?x system was constructed over a wide range of condensation temperatures (50–550°C) and molecular vapour flux densities R_+σ incident on the substrate (10²⁰-10²³ m^-2 s^-1). The thermoactivated disintegration of thin films (0.04-0.2 μm) of CdS_xTe_1?x solid solutions on vacuum annealing was investigated. Thermodynamically unstable films of composition 0.1 < x < 0.9 were shown to disintegrate at temperatures above 300°C, forming a two-phase system. Kinetic studies of the disintegration and of the phase changes occuring in the system were carried out. The contribution to the phase changes of the degree of structural dispersion in and the composition of the unannealed films is discussed.     

Applications of experimental techniques to solid mechanics and materials science research in telecommunications and electronics

In the effort to support the rational development of reliable, manufacturable leading edge communications technologies, a broad variety of experimental mechanics and materials techniques have been developed and/or applied at the AT& Bell Laboratories in Murray Hill, NJ. Much of the emphasis in this paper is on the application of optical methods to the conduct of experimental mechanics and materials research relevant to the telecommunications and electronics industries. It will also describe the role such research plays in supporting the development of a new process or product.
This paper is based on a presentation at the BSSM/SEM International Conference on "Advances in engineering measurements" held at The University of Edinburgh, 30 August to 01 September 1994.