Kinds Of Semiconductors Research Articles

ChemInform Abstract: LaF3 Thin Films as Chemically Sensitive Material for Semiconductor Sensors.

A new kind of semiconductor based fluoride sensor was prepared by growing thin polycrystalline LaF3 films directly on silicon substrates using vacuum vapour deposition technique. The EICS (Electrolyte Ion Conductor Semiconductor) structure was investigated by means of impedance spectroscopy, CV measurements and exchange measurements with labeled ions (18F). Whereas charge and potential conditions at the LaF3/ electrolyte interface are governed by the fast fluoride exchange the LaF3 bulk and the blocked Si/LaF3 interface determine the electrical behavior. Although the Si/LaF3 contact is not reversible the potential stability of the EICS structure is surprisingly high. Additional results at epitaxial LaF3 layers, prepared by MBE, were taken into account for comparision with those at polycrystalline layers.

Effects of addition of different carbon materials on the electrochemical performance of nickel hydroxide electrode

Nickel hydroxide is used as an active material in positive electrodes of rechargeable alkaline batteries. The capacity of nickel–metal hydride (Ni–MH) batteries depends on the specific capacity of the positive electrode and utilization of the active material because of the Ni(OH) 2/NiOOH electrode capacity limitation. The practical capacity of the positive nickel electrode depends on the efficiency of the conductive network connecting the Ni(OH) 2 particle with the current collector. As β-Ni(OH) 2 is a kind of semiconductor, the additives are necessary to improve the conductivity between the active material and the current collector. In this study the effect of adding different carbon materials (flake graphite, multi-walled carbon nanotubes (MWNT)) on the electrochemical performance of pasted nickel–foam electrode was established. A method of production of MWNT special type of catalysts had an influence on the performance of the nickel electrodes. The electrochemical tests showed that the electrode with added MWNT (110–170 nm diameter) exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage and cycling stability. The nickel electrodes with MWNT addition (110–170 nm diameter) have exhibited a specific capacity close to 280 mAh g −1 of Ni(OH) 2, and the degree of active material utilization was ∼96%.

Electrochemical investigation on addition of CNTs to the positive electrodes for Ni/MH rechargeable batteries

The active material β-Ni(OH) 2 of positive electrode for Ni/MH battery is a kind of semiconductor. Additives are necessary to improve the conductivity between the active material and the electric collector. Carbon nanotubes (CNTs) have been widely studied for their excellent electrical conductivity and good mechanical properties. In this work, the positive electrodes with CNTs for Ni/MH batteries were prepared and investigated by charge–discharge cycles. Compared to those with acetylene black, the electrodes with CNTs exhibited much better cycle stability, higher discharge voltage, and higher specific capacity. 0.5 wt.% was proved the desired amount and too much CNTs contributed no effect on the improvement of overall performance of the electrodes.

Reduction of Light-Decomposition and Enhancement of Photocatalysis of Photocatalyst by Au-Coat

Abstract A photocatalyst can be used for various applications. Such materials are semiconductors which are stable to photoirradiation, for example, TiO2. Most of these materials require UV light. There are many kinds of semiconductors which are unstable to photoirradiation, but which have a visible light response. In this study, it is shown that a thin Au film or Au nano particles on the surface of the photocatalyst reduced the photodecomposition of the photocatalyst. Although the surfaces of the samples were completely covered by Au, photocatalytic activity was observed in all the Au-coated samples. The Au-coating on the surface enhances the photocatalysis of a coated photocatalyst.

Universal analytical approximation of the carrier mobility in semiconductors for a wide range of temperatures and doping densities

A simple analytical method is suggested to calculate the mobility of majority carriers in semiconductors. The method allows one to adequately describe experimental data in a wide range of temperatures and doping levels in various kinds of semiconductors: elementary (Si), III-V (GaAs), IV-IV (various SiC polytypes), and III-N (GaN). The high accuracy of the results of the calculation suggests that the method is universal, and it may be used to calculate the mobility of majority carriers in other semiconductor materials. The simplicity and accuracy of the technique make it promising for computer simulations of multilayer semiconductor structures.

Optically-induced non-linear optical effects in indium–tin oxide crystalline films

We have studied thin nanolayers (with thicknesses of about 1–2 nm) between In2O3:Sn (indium–tin oxide (ITO)) crystalline films and glass substrates using the photo-induced optical second harmonic generation (PISHG) method. The maximal PISHG response observed for the pump–probe delay times was about 26 ps. The performed experimental measurements and quantum chemical theoretical simulations show that the observed effects are caused by two factors. The first is caused by the film–glass interface potential gradient and the second is a consequence of additional trapping levels appearing in the energy gap, particularly due to Sn doping. PISHG may be considered as a sensitive tool for such kinds of semiconductors.

Size Dependent Fluorescence Quenching of CdS Nanocrystals Caused by TiO2 Colloids as a Potential-Variable Quencher

The analysis of fluorescence quenching based on adsorption-desorption equilibrium between Q-CdS and TiO 2 allows the determination of the conduction band potential of Q-CdS and the estimation of surface hydroxylation of Q-CdS which takes place in solutions with pH greater than 10. The electron transfer from Q-CdS to TiO 2 occurs under activation control, and its rate depends on the potential difference in the conduction bands between the two kinds of semiconductors.

Microcrystalline silicon carbide — New useful material for improvement of solar cell performance

Abstract A new kind of semiconductor — doped microcrystalline silicon carbide (μc−Si(1−X)CX) — which is useful for improvement of photovoltaic performance has been developed. A series of experimental verifications on some unique properties such as high dark conductivity with good optical transparency in the solar spectrum is introduced. Then, the usefulness of this new functional material is demonstrated as the cases of wide gap window, front interface modifier, BSF (Back Surface Field) and RSOC (Rear Side Ohmic Contact) effects in the fabrication processes of a-Si and poly-Si sosed solar cells. The mechanisms of the performance improvement are studied and dicuussed. It could be expected that there exists a quite wide variety of availability for not only amorphous solar cells but also single crystalline and polycrystalline solar cells and photo imaging sensors.

Selective epitaxy of GaAs on indium oxide mask followed by in situ removal of the mask

The selective epitaxy of GaAs has been investigated on indium-oxide films prepared by vacuum deposition. It was found for the first time that gallium atoms supplied on the indium-oxide surface were absorbed into the oxide, resulting in the suppression of GaAs deposition on the oxide. The selective epitaxy on a patterned indium-oxide mask and subsequent in situ removal of the mask by radical hydrogen irradiation have been demonstrated. The investigation shows that indium oxide is a promising mask material for in situ processing since selective epitaxy up to 550 °C and in situ removal of the mask can be achieved on any kind of semiconductor.

Doping superlattices ("n-i-p-i crystals")

Semiconductors with doing superlattices exhibit a number of unique features by which they differ from uniform bulk crystals as well as from semiconductors with a compositional superlattice. The properties which make them particularly appealing as a new kind of semiconductor are tunability of carrier concentration, bandgap, two-dimensional subband structure, and recombination lifetimes, in combination with an enormous flexibility in tailoring. Moreover, the choice of host materials is not restricted by interface- or lattice-matching problems. The possibility of varying conductivity, absorption coefficient, optical gain, and luminescence spectra by light or external electrical potentials implies new concepts for photodetectors, tunable light sources, optical amplifiers, and modulators. The long recombination lifetimes result in large low-power nonlinearities of the optical absorption coefficient and the refractive index. These properties offer applications for saturable absorbers and bistable optical devices. In this paper the basic concept of doping superlattices and experiments which have provided its verification will be reviewed first. New physical phenomena and possible device applications will then be discussed. Finally, we will report some recent results of extensions of the concept to "hetero n-i-p-i's," obtained by periodic modulation of composition superimposed on the periodic n-i-p-i doping profile.

The Effects of Ion Beam Etching on Si, Ge, GaAs , and InP Schottky Barrier Diodes

The effects of ion beam etching (IBE) on the electrical properties of Schottky barriers on four kinds of semiconductors (Si, Ge, , and ) were investigated. For diodes processed with IBE after metal deposition where the active device region is protected by the metal layer and only the surrounding substrate area is exposed to the beam, our results showed that the diode breakdown voltages increased 2–15 times for p‐type substrates, but decreased 2–4 times for n‐type substrates. The barrier heights, , on p substrates were observed to remain unchanged, while the barrier heights, , were found to decrease on n substrates. For diodes processed with IBE before metal deposition, the diode characteristics are similar to those processed with IBE after metal deposition; the only notable exception is that the barrier heights on p substrates increased for this case, while remained unchanged for diodes processed with IBE after metal deposition. The effects of IBE are observed to disappear and the diodes recover to their original characteristics upon annealing at temperatures between 300° and 375°C. These effects are consistent with the concept that ion beam processing induces donor‐like defects near the surface region of the semiconductor exposed to the ions.

Heterogeneous photocatalytic reactions of organic acids and water. New reaction paths besides the photo-Kolbe reaction

The heterogeneous photocatalytic reactions of acetic, propionic, and butyric acids were studied on several kinds of powdered semiconductors, mainly TiO/sub 2/. The influence of Ag/sup +/ as an electron acceptor, and the dependence of the reactions on the kind of semiconductor and pH, were investigated. The ratio of yields of hydrogen to hydrocarbon depends strongly on pH. At neutral or alkaline pH, hydrocarbon stops being evolved and only hydrogen is evolved. It is concluded that the pH dependence of the valence band position of the semiconductor and the concentration of OH/sup -/ ion control the reaction paths. From the pH dependence of methane production from acetic acid the valence band of anatase is estimated to be located more deeply by 0.1 eV than that of rutile. The results of product analysis and the complete decomposition of acetic acid to CO/sub 2/ show that there exist new reaction paths in which water is an oxidizing agent. Reaction schemes of these organic acids are proposed.

Photoelectric Phenomena with Copper Phthalocyanine

ON the evidence of the dependence of electric conductivity upon temperature, Eley1 and Vartanyan2 reached the same conclusion, namely, that both phthalocyanine and its metallic derivatives should be regarded as kinds of semiconductors. In this connexion we wish to report that copper phthalocyanine exhibits the following photoelectric phenomena: (1) photoconductivity, (2) generation of electromotive force, and (3) change of the surface potential, both (2) and (3) being induced by illumination.

Theory of the F-centers of Coloured Alkali Halide Crystals. Part I

As is well-known, the various physical properties of semiconductors are essentially determined by the existence of the so-called quasi-atomic states in the forbidden region of energy band system characteristic for the body crystal. Since the lattice imperfections due to the inclusion of foreign atoms and stoichiometric excess-atoms, the internal cracks within the crystals or other mechanism may be considered to become possible origins which give rise to the mentioned quasi-atomic states, the consistent, theoretical attack of semiconductors will be necessarily confronted with a difficult problem of treating mathematically the imperfect crystals, while in the perfect crystals the method of solution of Schrödinger wave equation is well known to be much simplified owing to the periodicity and symmetry valid within the perfect crystals. In addition to the mentioned theoretical difficulty in solving the wave equation of the imperfect crystal, the vast experimental investigations of the physical properties of semiconductors reveal that even the experimental data of the same kind of semiconductors are always at variance with each other, showing the sensitive dependencies of the materials upon the experimental method of preparations. Such experimental difficulties to get the precise reproduction of the materials with consistent physical properties will become serious obstacles for proceeding the reliable physical considerations of the semiconductors. In view of the above situations both theoretical and experimental, therefore, it seems to be more enlightened at the present stage of the theory that the particularly simple semiconductors with reliable and systematic experimental data shall be thoroughly worked out theoretically in order to find a suitable method of approximation for solving the quasi-atomic states characteristic for semiconductors and then the theoretical method obtained shall be extended to those of the more complicated semiconductors accessible in both pure and applied fields of atomic physics. From the standpoint mentioned above, we shall here take the coloured alkali halide crystals which have been worked out experimentally by the systematic observations of Pohl and his coworkers, von Hippel and others. According to the experimental investigaions the colour-center, i.e., F-center responsible for the selective absorption of light and the colouration of the crystals may be considered to be typical ones of the mentioned quasi-atomic states whithin semiconductors. In Part I we shall work theoretically the detailed structure of F-absorption band peculiar to the alkali-halide crystals in connection with its temperature effect, and in Part II the general theory of trapped electrons within the quasi-atomic states of semiconductors shall be developed. The quasitative application of the general theory to the F-centers of NaCl crystal shall be attempted to do in comparison with the experimental observations in Part III.

Theory of the F-centers of Coloured Alkali Halide Crystals. Part I Structure of F-Absorption Bands

As is well-known, the various physical properties of semiconductors are essentially determined by the existence of the so-called quasi-atomic states in the forbidden region of energy band system characteristic for the body crystal. Since the lattice imperfections due to the inclusion of foreign atoms and stoichiometric excess-atoms, the internal cracks within the crystals or other mechanism may be considered to become possible origins which give rise to the mentioned quasi-atomic states, the consistent, theoretical attack of semiconductors will be necessarily confronted with a difficult problem of treating mathematically the imperfect crystals, while in the perfect crystals the method of solution of Schrödinger wave equation is well known to be much simplified owing to the periodicity and symmetry valid within the perfect crystals. In addition to the mentioned theoretical difficulty in solving the wave equation of the imperfect crystal, the vast experimental investigations of the physical properties of semiconductors reveal that even the experimental data of the same kind of semiconductors are always at variance with each other, showing the sensitive dependencies of the materials upon the experimental method of preparations. Such experimental difficulties to get the precise reproduction of the materials with consistent physical properties will become serious obstacles for proceeding the reliable physical considerations of the semiconductors. In view of the above situations both theoretical and experimental, therefore, it seems to be more enlightened at the present stage of the theory that the particularly simple semiconductors with reliable and systematic experimental data shall be thoroughly worked out theoretically in order to find a suitable method of approximation for solving the quasi-atomic states characteristic for semiconductors and then the theoretical method obtained shall be extended to those of the more complicated semiconductors accessible in both pure and applied fields of atomic physics. From the standpoint mentioned above, we shall here take the coloured alkali halide crystals which have been worked out experimentally by the systematic observations of Pohl and his coworkers, von Hippel and others. According to the experimental investigaions the colour-center, i.e., F-center responsible for the selective absorption of light and the colouration of the crystals may be considered to be typical ones of the mentioned quasi-atomic states whithin semiconductors. In Part I we shall work theoretically the detailed structure of F-absorption band peculiar to the alkali-halide crystals in connection with its temperature effect, and in Part II the general theory of trapped electrons within the quasi-atomic states of semiconductors shall be developed. The quasitative application of the general theory to the F-centers of NaCl crystal shall be attempted to do in comparison with the experimental observations in Part III.