The temperature dependence of the electrical conductivity in amorphous germanium

An investigation of the electrical conductivity in amorphous Ge has been made. It has been found that the temperature dependence of the conductivity can differ from the usually acceptedT ^–1/4 law. It has been shown that transition from the hopping-type conductivity can be influenced by the conductivity in extended states.Cukrovarnická 10, Praha 6, Czechoslovakia.We are grateful to dr. B. Velický for discussions about the subject matter of this paper and to Mr. J. Zemek for preparation of germanium samples.     

Slow non-exponential changes oe surface conductivity of germanium

A study was made of slow relaxation effects produced during changes in the external d-c electric field above the oxided surface of germanium and an empirical relation was found to describe their time dependence. It is seen that the activation energy of the control process, which is about 0·4 eV, can be determined from the temperature dependence of slow effects.

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, , , . , , 0,4 eV.

     

Influence of relative humidity on surface conductivity of germanium

A study was made of the influence of the relative humidity (from 0.5–90%) on the surface conductivity of bothp- andn-type germanium having differing resistivity. It was. found that the range of changes in the surface potential did not depend on the volume properties of germanium. An analysis of the experimental results shows that the surface potential has values approximately in the range from _s =–3kT/q to _s =+5kT/q for a change in humidity from 0.5 to 90%. Assuming that the Fermi level changes on the outer side of the oxide layer by approximately the same value as on the germaniumgermanium oxide boundary as a result of the increase and decrease of slow states, it follows that the levels of the slow centres are considerably distant from the Fermi level during the whole humidity range. It is also shown that on the first monomolecular layer of adsorbed water there is an increment of (7.5±0.8) x 10¹⁰ donor levels per cm². This increase in levels either decreases with the number of adsorbed monomolecular layers of water and for 90% humidity has approximately the value 2×10¹⁰ cm^–2 or remains almost unchanged with the number of layers, if it is assumed that for _s =6.0kT/q the Fermi level passes through the centres of adsorbed water.

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0,5 90% p n. . , _s =– 3kT/q _s =+ 5kT/q 0,5 90%. , - , , . , (7,5 ±0,8). 10¹⁰ cm². 90% . 2. 10¹⁰ cm^–2 , , , _s =6,0kT/q .

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In conclusion the author thanks Dr. J. Taue for instigating this work and S. Koc, C. Sc., for remarks and the interest with which he followed the work. He also thanks A.Müller for measuring the Hall constant in the samples.     

Thermoelectric power and electrical conductivity of sputtered amorphous germanium: Effect of annealing

Detailed measurements of the temperature dependence of dc electrical conductivity(T) and the thermoelectric powerS(T) at different annealing stages of sputtered amorphous (a-Ge) and polycrystalline germanium (c-Ge) layers in the range 80–430 K are reported. The sign ofS of the polycrystalline layers is positive. On the other hand the sign ofS of the a-Ge is always negative. At low temperature theS(T) dependences of a-Ge are constant and weakly depend on annealing. In the high temperature region the ¦S(T)¦ curves reach maximum values and depend relatively strongly on annealing. In the low temperature range the(T) dependences satisfy the T^–1/4 Mott's law. Annealing shifts the(T) towards lower values especially at low temperature. The(T) andS(T) data of a-Ge are discussed on the basis of a proposed model of the hopping conduction within the mobility gap.The author expresses thanks to Dr. S.Koc, Dr. Z.ima, Dr. V.Vorlíek and Dr. I.Gregora for helpful discussions.     

Work function measurements on germanium by thermionic emission

In the present paper, we report the results of experiments carried out to determine the effect of surface states on the work function of intrinsic, germanium crystals. This investigation is realised by using the Thermionic Emission Theory at the intrinsic temperature range T (from 900 to 1050 K). The “apparent work function” φ¹, obtained from the experimental ln(i_sT²) versus 1/T curves, is found different from the Richardson-Dushman equation one: “the true work fucntion” φ. This difference is mainly due to the work function and electron reflection coefficient dependence on temperature. φ is deduced from φ¹ and from RD modified equation taking into account the semiconductor case. The value of φ varies with T: from 3.97 to 4.16 eV. These results are compared with those obtained, by several authors, using other techniques. We present an analysis of these results taking into consideration the effect of surface states shifts on the surface barrier height, and on the work function consequently.     

Influence of copper ions and the crystallographic orientation on the surface properties of germanium in contact with an electrolyte

The activation peculiarities and trapping and recombination center parameters caused by copper ion adsorption on a differently oriented germanium surface in contact with a neutral electrolyte were investigated. It is shown that the anisotropy of the fast surface state (FSS) parameters, including the recombination centers, agrees with those for a “pure” and a gold-doped surface, while the activation kinetics is closer to the silverdoped case. From a comparison between the results obtained in this paper and earlier results there follows that the individuality of the metal does not appear essentially in the parameters of activated FSS since these latter are quite close in all cases. It can be assumed that the metal-germanium surface layer bond is the only necessary condition for the generation of a definite kind of structural defects which perform the role of recombination and trapping centers.     

Thermochemical nitridation of sapphire substrates of different crystallographic orientations

This paper presents the results of the study of the influence of physicochemical parameters of thermochemical nitridation of sapphire substrates of different crystallographic orientations in an N₂ + (CO,H₂) reducing atmosphere on structural characteristics, composition, and kinetics of AlN layer formation. The effective diffusion coefficients of nitrogen in sapphire at T = 1473?1773 K have been determined. The temperature dependences of the structural quality, thickness, and roughness of the AlN layer surface have been found; their strong dependence on the composition and reduction potential of the nitridation atmosphere has been shown. The structural models of matching the AlN and sapphire lattices during thermochemical nitridation have been proposed.     

Laser-stimulated conductivity of amorphous germanium films

It is shown that metastable states are created in evaporated -Ge films by laser irradiation. The lifetime of the metastable state is a strong function of the incident laser power density.Supported by IRSIA (Brussels)     

Memory function approach to the Ziman formula for the electrical conductivity in liquid metals

The Ziman formula for the electrical conductivity and its generalization including dynamical correlations are discussed from the memory function approach.     

Influence of surface roughness on the electrical conductivity of semiconducting thin films

The Green function solution of the Boltzmann transport equation has been applied in case of no magnetic field by ignoring any volume impurities. Gaussian, exponential and power law models for the surface roughness correlation function have been studied and the results have been compared with the ones obtained by other methods. It has been found that the electrical conductivity σ$\sigma$ increases with increasing correlation length l$l$ for the first two models, while for the third model σ$\sigma$ value is of the same order as the first two models. Therefore we show that the shape of the surface roughness can strongly influence the electrical properties.     

Investigation of gallium arsenide single crystals with various crystallographic orientations, after implantation of silicon ions and pulsed photon annealing

The results of experimental investigations of gallium arsenide single crystals with the orientations (100), (311)A, (211)A, (111)A, and (221)A are presented. The crystals were doped with silicon ions on the Iolla-3M setup (ion energy 75 keV, ion beam density 1 μA/cm², implantation dose 1.2×10³ cm⁻²) at room temperature and annealed on the Impul’s-5 setup at 950°C. Raman scattering and low-temperature photoluminescence methods established that the highest electrical activity of the implanted silicon under identical implantation and annealing conditions obtains for (100) and (311)A gallium arsenide. In the process n-type layers are produced. Zh. Tekh. Fiz. 69, 78–82 (May 1999) Deceased.     

Tabular electrical conductivity for aluminium

A new Sesame-type table for the electrical conductivity of aluminium is described. The table is based on density functional theory calculations and ranges from 10⁻³ to 1 times solid density (2.7 g/cm³), and from 10⁻² to 10³ eV in temperature. The table is compared with other those of simulations and to experiments and is generally in good agreement. The high-temperature, classical limit of the conductivity is recovered for the highest temperatures and lowest densities. The table is critically evaluated, and directions for improvements are discussed.     

Electrical conductivity of germanium with dislocation grids

Samples of n-type germanium with a donor concentration N _d=2.4×10¹⁶ cm⁻³ are plastically deformed to a degree of strain equal to 18–40% to detect static conduction by electrons trapped on dislocations in a system of dislocation grids. In samples with 20%<δ<31%, which retain an electronic type of conductivity, the conductivity for T<8 K, which is weakly temperature-dependent, is associated with conduction by electrons trapped on dislocations. The nonmonotonic dependence of the conductivity at 4.2 K on the degree of strain as the latter increases from 18% to 40% attests to the existence of an energy gap between the donor and acceptor dislocation states in strongly plastically deformed germanium. Zh. éksp. Teor. Fiz. 115, 115–125 (January 1999)     

Enhanced electrical surface conductivity of LiNbO3 induced by argon-ion bombardment

The surface conductivity of pure and proton exchanged LiNbO₃ was studied. After bombarding the surface with Ar⁺ ions having an energy of about 2000 eV the samples showed an enhanced specific conductivity near the surface (5 nm) of 6 orders of magnitude. This corresponds to a specific conductivity of 10^–5 S/cm at room temperature. The enhanced conductivity is thermally activated with an energy of 0.41±0.04 eV, and it seems to be a non-ionic conductivity, because no polarization behaviour was observed. This enhanced conductivity was observed at the surface of both pure and proton exchanged LiNbO₃.     

Low-temperature thermal conductivity of highly enriched and natural germanium

Experimental data on the thermal conductivity K(T) of crystals of natural and highly enriched germanium (99.99%) ⁷⁰Ge with lapped and polished surfaces are analyzed in the temperature range ∼1.5–8 K. In all the samples in the temperature range ∼1.5–4 K the standard boundary mechanism of scattering dominates. As the temperature is raised, an isotopic scattering mechanism is observed in the natural samples. In the highly enriched samples the theoretical values of K(T) turn out to be much smaller than the experimental ones. It is conjectured that a Poiseuille viscous flow regime of the phonon gas emerges in this case. Zh. éksp. Teor. Fiz. 114, 1757–1764 (November 1998)