Conductivity Of Germanium Research Articles

Isotope effect in the thermal conductivity of germanium single crystals

The thermal conductivity of chemically, structurally, and isotopically highly pure germanium single crystals is investigated experimentally in the temperature range from 2 to 300 K. It is found that the thermal conductivity of germanium enriched to 99.99% 70Ge is 8 times higher at the maximum than the thermal conductivity of germanium with the natural isotopic composition.

Low-temperature conduction in germanium with disorder caused by extended defects

Investigations were carried out on low-temperature conductivity in the defect band of germanium formed due to the presence of large concentrations of extended defects introduced during high-temperature plastic deformation or irradiation with large integrated fluxes of high-energy neutrons and protons. It has been demonstrated that at relatively low concentrations of dislocations and low temperatures the electrical conductivity in the defect band occurs by hopping. At higher concentrations of dislocations the metal-insulator transition (MIT) takes place in the system of dislocations, the conductivity near the MIT showing a power-law variation, sigma (T) approximately Tx, with x<or=1 in the range 30 to 3*10-2 K. It has also been shown that the dislocation conductivity has a quasi-two-dimensional character. The dynamics of the Coulomb gap variations was studied near the MIT in Ge with a high concentration of radiation defects. The experimental data presented show that Ge with a high concentration of dislocations can be used for simulating some physical phenomena in amorphous and vitreous semiconductors.

Longitudinal phonons and high-temperature heat conduction in germanium

Using the relaxation time approach, the authors present a new analysis of phonon conductivity which shows that at high temperature (T> theta D, the Debye temperature), the longitudinal phonons are the dominant heat carriers in germanium. The present result, which is a consequence of the effect of phonon dispersion on the Callaway integral for lattice thermal conductivity, is contrary to the general belief that transverse phonons carry heat at T> theta D. A qualitative justification has also been given for the three-phonon scattering parameters obtained.

Synthesis and Conductivity of Germanium- or Silicon-Containing Polymers

Abstract Poly[{(E)-1,1,2,2-tetramethyldigermanylene}ethenylene], poly[(1,1,2,2-tetramethyldigermanylene)-2,5-thienylene], poly[(1,2-dimethyl-1,2-diphenyldigermanylene)-p-phenylene], and poly(methylphenylgermylene) were synthesized. SbF5 doping of above polymers showed the conductivities of the order of 10−4 S/cm, which were similar to, or a little higher than, those of corresponding silicon analogues.

Exciton Impact Ionization and Electric Conductivity in Germanium at Low Temperature

AbstractThe exciton luminescence intensity and the electric conductivity are measured simultaneously during optical excitation in high‐purity Ge and in p‐doped Ge at 4.2 K as a function of an applied electric field. With increasing field the exciton density decreases due to exciton impact ionization. The carriers which are set free by this process result in a distinct increase in the electric conductivity. For undoped Ge the results agree well with a rate equation model based on impact ionization of the excitons. In the p‐doped Ge impurity impact ionization is found to have a strong influence in addition to impact ionization of the excitons.

Photoluminescence and electric conductivity in germanium at low temperatures

We have studied the exciton and electron-hole droplet (EHD) luminescence in optically irradiated germanium at temperatures between 1.8 and 4.2 K in the presence of an electric field. Simultaneously the electric conductivity was measured. The sample material was high-purity Ge (NA−ND=7·1010 cm−3) andp-doped Ge withNA=3·1014 cm−3. In the high-purity Ge samples the exciton and EHD-luminescence intensity decreased nearly linearly as a function of the applied electric current, whereas the dependence upon the electric field was more complicated. Our results could be explained by a model in which carrier annihilation at the contacts following a rapid drifting process plays a dominant role (drift model). In thep-doped Ge samples the current-dependence of the luminescence intensity was qualitatively similar. However, here the drift model is not strictly valid any more because of the reduced carrier mobility and the generation of additional carriers by impurity impact ionization. During variation of the electric field, the luminescence intensity and the electric current show hysteresis. Here the capture of the moving carriers by the EHD appears to play an important role, in addition to the EHD-nucleation process.

Thermal conductivity of germanium doped with silicon, tin, and aluminium

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The electrical conductivity and magnetic susceptibility of germanium(II) monoselenide in the solid and liquid states

The specific conductivity of germanium(II) monoselenide has been measured, under equilibrium pressure, from room temperature to 802°C. Interpretation of the results leads to the conclusion that the intrinsic conductivity is observed in the solid in the upper temperature range: the calculated energy gap is E 0g = 1.222 ± 0.027 eV which coincides with the value of the optical gap. In liquid GeSe the calculated energy gap is 1.504 ± 0.016 eV. This increase of the energy gap in liquid GeSe is due, presumably, to the strengthening of the intralayer bonds of the structure. Electrical conductivity and magnetic susceptibility measurements confirm the existence of a polymorphic transformation in GeSe at 656°C.

The deformation potentials of the X‐valleys of the germanium conduction band

The deformation potentials of the X‐valleys of the germanium conduction band

Thermal conductivity of germanium containing dislocations at low temperatures

AbstractTo study the frequency dependence of the phonon–dislocation scattering, the phonon conductivity of germanium with dislocations is analysed using Holland's model and Kumar and Sinha's relaxation time for the phonon–dislocation scattering processes. A reasonably good agreement is observed between present theory and experimental data of Sato and Sumino.

Thermal conductivity of germanium at low temperatures

Thermal conductivity of germanium at low temperatures

Frequency Dependence of Warm Carrier Conductivity in Germanium

AbstractThe frequency dependence of the warm carrier conductivity in n‐ and p‐Ge is measured in the frequency range 0.4 to 150 GHz. The experiments are carried out at 80 and 273 K. A phenomenological theory of the warm carrier conductivity for the semiconductor having two degenerate bands at k = 0 is developed. By applying this theory to the experimental data it is shown that in p‐Ge at 80 K the warm carrier conductivity relaxation process at microwave frequencies is strongly influenced by the hole interband repopulation effect. The values of the energy relaxation time τϵ are evaluated for both materials at both temperatures. It is established that τϵ in p‐Ge is isotropic and the anisotropy of the conductivity relaxation time observed is caused by the warping of the constant‐energy surfaces of heavy holes.

Role of internal boundary scattering and modifications in Casimir ’s theory

The assumption of perfect roughness of crystal boundaries is modified by considering a partially reflecting, absorbing and rough crystal surface which would make changes in crystal microboundaries and develop the strains inside the crystals to grow internal boundaries. The development of microboundaries and internal strains would shorten the phonon mean free paths and demand a modification in Casimir’s theory. The modified Casimir length describes larger thermal resistance. The heat conductivity of germanium and Mg2Sn in the low-temperature range is calculated. in encountering the internal-boundary scattering, and successful agreements with experimental data are obtained.

Conduction electrons in an impurity band: NMR in Ge:As

The 73Ge spin-lattice relaxation time T1 has been studied at 4.2K and below in single-crystal specimens of arsenic-doped germanium (Ge:As), with doping densities spanning the metal-non-metal transition. An increase of T1 with the applied magnetic field is observed for both semiconducting and the low-density metallic 'impurity-banded' materials, although T1 is independent of field for heavily doped metallic samples. The behaviour in the metallic region is interpreted here using two models of the band in which the conduction electrons move, based on the tight-binding and rigid-band approaches, and the results are compared with those of other workers in the related Si:P system. Very little support can be adduced from this work for the dominance of correlation as the driving mechanism for the metal-non-metal transition in Ge:As. The results indicate that the metal-non-metal transition in Ge:As occurs when the impurity band heavily overlaps the germanium conduction band.

Valley-Orbit Splitting of Li in Ge

The thermal conductivity of germanium doped with lithium in the isolated impurity range has been measured between 0.4 and 20 K. The analysis of the electron-phonon scattering leads, for the first time, to a determination of the valley-orbit splitting (0.12 meV) of the ground state of the interstitial Li donor in Ge.

Electrical conductivity of germanium as a function of optically injected carrier density and temperature

The effects of carrier-carrier scattering on the transport properties of high-density electron-hole plasmas in germanium were studied both experimentally and theoretically. Experimentally, the dc electrical conductivities of nearly uniform optically injected bipolar plasmas in high-purity single crystals of germanium were measured for a broad range of carrier densities (\ensuremath{\sim} ${10}^{14}$ - \ensuremath{\sim} 5 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) and temperatures (21-298 K). Concurrent measurements of the absorption of 3.39-\ensuremath{\mu}m radiation due to inter-hole-band transitions aided the calibration of the carrier densities at some temperatures. The previous theory of Appel, which used Kohler's variational principle to solve the Boltzmann equation, was generalized with respect to the inclusion of interband hole scattering, electron mass anisotropy, degeneracy, and use of the RPA $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$-dependent screening approximation (although not with respect to all at once). The most crucial generalization was the accounting for the presence of nonconducting excitons in the plasma. The scattering of free carriers by excitons was also considered, using a neutral-impurity scattering theory similar to that of Erginsoy. Incorporation of all the above considerations led to excellent agreement between experiment and theory at densities below the Mott criterion for transition to the exciton-free phase. The transition itself appeared to be gradual, however, and behavior of the conductivity in the high-density region was consistent with the recent assertion by Thomas and Rice that excitons are present at densities significantly above the Mott criterion.

Effects of etching and oxidation on the thermal conductivity of germanium

Effects of etching and oxidation on the thermal conductivity of germanium

Effect of Dislocations on the Low Temperature Thermal Conductivity in Germanium

The thermal conductivity vs temperature relation in deformed germanium single crystals is measured in the temperature range from 1.5 to 30 K. The results are analysed on the basis of the Callaway model. Klemens' theory on the scattering of phonons due to the static strain field of dislocations accounts for the experimental results reasonably well. The dislocation densities deduced from the thermal conductivity data are greater than those counted by direct observation of dislocations by factors less than 3.7 and 2.1 in specimens deformed to stage I and stage II, respectively. Discrepancies between the theoretical curves and the experimental curves are found at temperatures around 20 K and below 2.2 K. The former is accounted for by assuming that point-defect like imperfections have been introduced into specimens during deformation, while the latter could be attributed to the scattering of phonons due to dangling electrons located at the dislocation core.

Simple Variational Calculation of Thermal Conductivity at Low Temperatures

A simple method for the variational calculation of the thermal conductivity at very low temperatures is proposed in this paper. Isotropy and the absence of dispersion in the crystal vibrational spectrum are assumed. No distinction is made between transverse and longitudinal phonons. The assumed scattering mechanisms are (i) boundary scattering and (ii) mass-defect scattering. The trial function is chosen to be a power-series expansion in frequency. The thermal conductivity of germanium is calculated by applying the present method for the temperature range 2-20 \ifmmode^\circ\else\textdegree\fi{}K. At sufficiently low temperatures (2-10 \ifmmode^\circ\else\textdegree\fi{}K), the calculated results are in reasonably good agreement with the experimental results without using any adjustable parameter. For temperatures greater than 10 \ifmmode^\circ\else\textdegree\fi{}K, the calculated results show the presence of other scattering processes.

Slow relaxation of charge on germanium surface

Abstract The processes associated with the slow relaxation of the surface conductivity of germanium were studied. The observed known exponential dependence of the slow relaxation processes was found to be related to the inhomogeneities of the surface with regard to relaxation times.