L. Štourač

The structure and electronic properties of semiconducting glasses based on CdAs2

Abstract A new group of amorphous substances based on CdAs 2 has been studied. Glasses are produced if elements of Ge, Si, Mg, Ga, In, Tl and Sb are added to the CdAs 2 melt. A special property of these glasses is that at a temperature of 360 to 410°C they recrystallize. From an analysis of the curves of radial distribution of the atom density we deduce that the basic unit of the structure of such glasses is the tetrahedron CdAs 4 . A mechanism has been proposed for the formation of such glasses and some of its features have been verified by measuring the magnetic susceptibility. Measurements of the shape of the absorption edge and the electrical conductivity show that such glasses have a semiconducting character. The shape of the absorption edge and the dependence on temperature indicate that Urbachs rule holds. The electrical conductivity follows the relation σ = σ 0 exp ( − ΔE /2 kT ); usually it is very low in most glasses and at room temperature is of the order of 10 −6 to 10 −7 (Ω cm) −1 . The activation energy ΔE ≅1 eV does not change very much with the composition of the glass. Exceptions are antimony and thallium glasses, the latter in particular having a relatively high electrical conductivity and ΔE depending strongly on the Tl content. A switching effect was observed in amorphous stoichiometric CdGeAs 2 .

Field effect in dc-sputtered a-Si:H in structure using SiNx prepared in situ

Abstract A series of experiments which aimed at improving the performance of field effect in a structure with a-Si:H prepared by dc sputtering has been carried out. The dielectric properties of an SiO 2 layer, used originally as an insulator, deteriorate during the deposition process. We succeeded in preparing a protective layer of SiN x deposited in situ . An increase of the source-drain current by three orders of magnitude in the improved structure is reported. Values of the field effect mobility are calculated from the temperature dependence of the field effect. The possibility for the improvement in performance of these structures is discussed.

Electronic properties of glassy As2Te3

Bulk samples of glassy As2Te3 and its alloys with Ge, Si or Tl were prepared by quenching of the melt and their electrical, photoelectrical, optical and thermodynamical properties were studied. The addition of Ge, Si or Tl produces three different types of glass from the thermodynamical point of view; the physical properties studied differ only quantitatively.

The role of interface states in the evaluation of density of states from field effect measurements in dc-sputtered a-Si:H

Abstract We have succeeded in preparing FET type structure with a protective SiN x layer which enabled us to observe the largest field effect (FE) reported on dc-sputtered a-Si:H. The role of the interface states is demonstrated by a comparison of the density of states (DOS) deduced from the FE in structure with and without the protective layer and that from the analysis of space-charge-limited currents (SCLC) in heterojunction with a-Si:H prepared under the same conditions.

Influence of microgravity on the physical and crystallochemical properties of glassy GeSSb

Abstract The first results of the study of glassy Ge25S55Sb20, prepared under microgravity and terrestrial conditions are reported. It is shown that glass prepared under microgravity conditions is more homogeneous and exhibits less tendency to recrystallization. Its optical and electrical properties are compared and discussed.

Amorphous-Crystalline Heterojunctions

Investigation of amorphous-crystalline (a/c) heterojunctions is useful both for the understanding of the fundamental device physics and for applications. In some cases it can also give important information about physical parameters of amorphous semiconductors.

Schottky barrier on n-GaAs formed by amorphous tungsten silicide

We have prepared amorphous tungsten silicides with different contents of tungsten by a.c. magnetron co-sputtering. For silicon to tungsten ratio smaller than 0.1, silicides have a metallic character. This material is suitable for Schottky contacts formation on n-GaAs.

Gaps and Electronic States in Tetrahedrally Bounded Amorphous GeS

Experimental results of the investigation of the reflectivity, optical absorption, photoconductivity and electrical conductivity on both crystalline and amorphous GeS are reported and critically compared.

Ultrasonic investigation of dynamic properties of the amorphous network

The changes of dynamic properties of amorphous selenium during the relaxation process to the new equilibrium state are investigated using the ultrasonic attenuation measurements. From their temperature dependence the distribution of the activation energies is determined. The relation between ac electric losses and acoustic losses is demonstrated.