V. Šmíd

On space-charge-limited conduction in semi-insulating GaAs

Abstract We have measured the temperature dependence of Cr doped semi-insulating (SI) GaAs in planar and point contact configurations at various fields ranging between 10 and 10 6 V/m. In a planar configuration the transport is ohmic up to ∼ 10 4 V/m with an activation energy of ∼ 0.75 eV. At higher fields we have observed a space-charge-limited (SCL) transport with an activation energy of about 0.47 eV. In a point contact configuration a quasi-ohmic and a transitional region have been found, both having an activation energy of ∼ 0.47 eV. Such behaviour is in qualitative agreement with Lamperts theory of SCL conduction. Some deviations from this theory are accounted for by the existence of macroscopic screening length in SI-GaAs.

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.

A comparison of picts with direct measurements of non-exponential current transients on Si-GaAs

Abstract We demonstrate a good correspondence of the results obtained by PICTS and by fitting isothermal current transients when a multiexponential form with well separated exponentials can be used for a description of the transients and at the same time the PICTS spectra give a linear Arrhenius plot. The results are also supported by TSC measurements below the room temperature. All the measurements have been performed on samples with a three electrode configuration which makes it possible to separate surface and bulk related signals. It has turned out that the negative peak observed on our samples in the PICTS spectra above the room temperature cannot be explained by surface related phenomena only. This is to our knowledge the first direct experimental proof of the nature of the negative peak which has recently been a subject of discussion in the literature.

On the d.c. conductivity in semi-insulating GaAs

Abstract We investigate the temperature dependence of electrical conductivity of SI-GaAs. We have shown that the surface conductivity obeys the Berthelot type of dependence, the bulk component, on the other hand, fulfills the Arrhenius dependence.

Amorphous nickel silicides prepared by magnetron co-sputtering

Abstract We have investigated properties of amorphous nickel silicides with different amount of metal ranging from 0 to ∼ 17 at. %. We discuss the transport mechanisms in silicides as well as the shift of the optical absorption edge with the Ni content.

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.

A comparison of different types of signal processing in PICTS measurements

Abstract Experimental comparison of a standard and so-called four-gate processing in PICTS measurements is shown. The differences between these methods are demonstrated when the pre-exponential transient factor modifies the standard PICTS spectra under non-ideal physical conditions. Direct isothermal transient measurements were performed in selected cases.

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.

Comparison of PICTS measurements on Si-GaAs interpreted within generalized physical models

Abstract Experimental data measured by the Photo-Induced Current Transient Spectroscopy (PICTS), i.e. the temperature positions of maxima in PICTS spectra versus the time positions of boxcar gates, have been fitted within physical models with different stage of generalization. This procedure has been applied to several important deep levels observed in semiinsulating undoped and chromium doped GaAs crystals and the obtained results have been compared with each other.