Conductivity Of Germanium Research Articles

Ab initio prediction of metallic nature of sp3-hybridized germanium structures

Guided by Density Functional Theory within the bounds of GGA/PBE theory, we study the electronic, energy, mechanical and ballistic conductivity of germanium [n,m]-prismanes. The prismatic structure is a cylinder, with a m-vertices polygon (germanium ring) at the foot and an n-number of such polygons along the growth direction of the nanotube. As depicted, the finite prismanes reduce their band gap with an increase in the number of rings and periodic systems have metallic conductivity. It is established that metallic properties are resistant to the stress applied along the main axis of the prismanes.

Dual carbon decorated germanium-carbon composite as a stable anode for sodium/potassium-ion batteries

In the present work, we introduce a dual carbon accommodated structure in which germanium nanoparticles are encapsulated into an ordered mesoporous carbon matrix (Ge-CMK) and further coated with an amorphous carbon layer (Ge@C-CMK) through a nano-casting route followed by chemical vapor deposition (CVD) treatment. In the resultant Ge@C-CMK composite, the unique lane-like pore structure that cooperates with the amorphous carbon surface can not only mitigate the volume expansion of germanium particles, but also improve the electrical conductivity of germanium as well as facilitate Na+/K+ diffusion. When employed as the anode of sodium-ion batteries, the Ge@C-CMK electrode exhibits stable capacity as well as long-term cycling stability (a stable capacity of 176 mAh g−1 at 1 A g−1 after 5000 cycles). Furthermore, it also delivers a reversible capacity when used as the anode of potassium-ion batteries. This demonstrates that the Ge@C-CMK electrode possesses promising application potential as an alternative anode in sodium and potassium ion storage applications.

Low-temperature intracenter relaxation times of shallow donors in germanium

The relaxation times of localized states of antimony donors in unstrained and strained germanium uniaxially compressed along the [111] crystallographic direction are measured at cryogenic temperatures. The measurements are carried out in a single-wavelength pump–probe setup using radiation from the Novosibirsk free electron laser (NovoFEL). The relaxation times in unstrained crystals depend on the temperature and excitation photon energy. Measurements in strained crystals are carried out under stress bar S > 300, in which case the ground-state wavefunction is formed by states belonging to a single valley in the germanium conduction band. It is shown that the application of uniaxial strain leads to an increase in the relaxation time, which is explained by a decrease in the number of relaxation channels.

Effect of irradiation with 15-MeV protons on the compensation of Ge〈Sb〉 conductivity

The processes of the compensation of n-type conductivity in germanium irradiated with 15-MeV protons are investigated. Irradiation results in a considerable reduction in the density of shallow donor states of Group-V atoms. The rate of removal of shallow donor states due to the interaction between impurity atoms and radiation-induced intrinsic point defects is ~215 cm–1. The majority of secondary defects produced under proton irradiation are electrically neutral in an n-type material. Radiation-induced acceptors are of little importance in this case. Numerical modeling is performed, and the distribution of the energy transferred to recoil atoms is obtained. Two energy intervals are considered in the analysis of distribution histograms. At low energies, individual Frenkel pairs with closely spaced components are produced. The energy of recoil atoms in the second energy region is sufficient to induce a displacement cascade. Nanoscopic regions with high densities of intrinsic point defects and their complexes with dopant atoms are formed in such cascades. A model of the generation of intrinsic defects in germanium under proton irradiation is discussed.

Thermal conductivity from approach-to-equilibrium molecular dynamics

We use molecular dynamics simulations to study the thermal transport properties of a range of poor to good thermal conductors by a method in which two portions are delimited and heated at two different temperatures before the approach-to-equilibrium in the whole structure is monitored. The numerical results are compared to the corresponding solution of the heat equation. Based on this comparison, the observed exponential decay of the temperature difference is interpreted and used to extract the thermal conductivity of homogeneous materials. The method is first applied to bulk silicon and an excellent agreement with previous calculations is obtained. Finally, we predict the thermal conductivity of germanium and α-quartz.

Transition from spin accumulation into interface states to spin injection in silicon and germanium conduction bands

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in the electrical spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. Here we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of n-Si and n-Ge using a CoFeB/MgO tunnel contact. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from approximately 150 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with the standard spin diffusion model. More interestingly, in the case of germanium, we demonstrate a significant modulation of the spin signal by applying a back-gate voltage to the conduction channel. We also observe the inverse spin Hall effect in Ge by spin pumping from the CoFeB electrode. Both observations are consistent with spin accumulation in the Ge conduction band.

Crossover from Spin Accumulation into Interface States to Spin Injection in the Germanium Conduction Band

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in the spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. In this Letter, we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of n-Ge. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from 200 K up to room temperature. In this regime, the spin signal is reduced to a value compatible with the spin diffusion model. More interestingly, the observation in this regime of inverse spin Hall effect in germanium generated by spin pumping and the modulation of the spin signal by a gate voltage clearly demonstrate spin accumulation in the germanium conduction band.

Electrical and thermal spin accumulation in germanium

In this letter, we first show electrical spin injection in the germanium conduction band at room temperature and modulate the spin signal by applying a gate voltage to the channel. The corresponding signal modulation agrees well with the predictions of spin diffusion models. Then, by setting a temperature gradient between germanium and the ferromagnet, we create a thermal spin accumulation in germanium without any charge current. We show that temperature gradients yield larger spin accumulations than electrical spin injection but, due to competing microscopic effects, the thermal spin accumulation remains surprisingly unchanged under the application of a gate voltage.

Effect of normal processes on thermal conductivity of germanium, silicon and diamond

The effect of normal scattering processes is considered to redistribute the phonon momentum in (a) the same phonon branch — KK-S model and (b) between different phonon branches — KK-H model. Simplified thermal conductivity relations are used to estimate the thermal conductivity of germanium, silicon and diamond with natural isotopes and highly enriched isotopes. It is observed that the consideration of the normal scattering processes involving different phonon branches gives better results for the temperature dependence of the thermal conductivity of germanium, silicon and diamond with natural and highly enriched isotopes. Also, the estimation of the lattice thermal conductivity of germanium and silicon for these models with the consideration of quadratic form of frequency dependences of phonon wave vector leads to the conclusion that the splitting of longitudinal and transverse phonon modes, as suggested by Holland, is not an essential requirement to explain the entire temperature dependence of lattice thermal conductivity whereas KK-H model gives a better estimation of the thermal conductivity without the splitting of the acoustic phonon modes due to the dispersive nature of the phonon dispersion curves.

Germanium enhanced large-grain growth by pulse mode rapid thermal crystallization process

The large-grain crystallization for silicon film was implemented by doping germanium in silicon film and using a rapid thermal process with near-infrared illumination. Germanium atoms acted as nuclei for crystallization of the amorphous silicon film. Because the germanium embedded in silicon film could absorb infrared photonic energy and convert it into thermal energy. Due to the low thermal conductivity of germanium, the absorbed energy remained in the germanium-doped film for a long time and helped the grain growth. With the amount of germanium in silicon film increased, a large grain will be obtained readily. A grain size of 3.92 μm was achieved in germanium-doped film.

Isotope-concentration dependence of thermal conductivity of germanium investigated by molecular dynamics

Thermal conductivity of solid germanium as a function of the mole fraction of isotopes was estimated semi-quantitatively by using equilibrium molecular dynamics. The thermal conductivity of isotope-germanium was calculated by using an empirical potential of Stillinger–Weber potential. We employed the molecular dynamics based on Green–Kubo’s formula in which the autocorrelation function of heat flux was integrated as a function of duration time. The results of calculation showed that thermal conductivity of mixed isotope-germanium with large difference of mass is smaller than that with small mass difference, which is similar to experimental results.

Role of Phonon Dispersion in Lattice Thermal Conductivity Modeling

The role of phonon dispersion in the prediction of the thermal conductivity of germanium between temperatures of 2 K and 1000 K is investigated using the Holland approach. If no dispersion is assumed, a large, nonphysical discontinuity is found in the transverse phonon relaxation time over the entire temperature range. However, this effect is masked in the final prediction of the thermal conductivity by the use of fitting parameters. As the treatment of the dispersion is refined, the magnitude of the discontinuity is reduced. At the same time, discrepancies between the high temperature predictions and experimental data become apparent, indicating that the assumed heat transfer mechanisms (i.e., the relaxation time models) are not sufficient to account for the expected thermal transport. Molecular dynamics simulations may be the most suitable tool available for addressing this issue.

Normal processes of phonon-phonon scattering and the drag thermopower in germanium crystals with isotopic disorder

A strong dependence of the thermopower of germanium crystals on the isotopic composition is experimentally found. The theory of phonon drag of electrons in semiconductors with nondegenerate statistics of current carriers is developed, which takes into account the special features of the relaxation of phonon momentum in the normal processes of phonon-phonon scattering. The effect of the drift motion of phonons on the drag thermopower in germanium crystals of different isotopic compositions is analyzed for two options of relaxation of phonon momentum in the normal processes of phonon scattering. The phonon relaxation times determined from the data on the thermal conductivity of germanium are used in calculating the thermopower. The importance of the inelasticity of electron-phonon scattering in the drag thermopower in semiconductors is analyzed. A qualitative explanation of the isotope effect in the drag thermopower is provided. It is demonstrated that this effect is associated with the drift motion of phonons, which turns out to be very sensitive to isotopic disorder in germanium crystals.

Thermal conductivity of germanium, silicon, and carbon nitrides

We present a model calculation of the thermal conductivity of germanium nitride, silicon nitride, and carbon nitride in a temperature range in which intrinsic phonon scattering is dominant. We show that, in spite of the rather complex crystal structure of these nitrides, thermal conductivities exceeding 100 W m−1 K−1 can be attained in some of these compounds due to the combination of high Debye temperature and small Grüneisen constant.

Band structures of Ge and InAs: A 20 k.p model

The band structure of direct-band-gap semiconductor (InAs) and indirect-band-gap semiconductor (Ge) is described theoretically using a 20×20 k.p model and including far-level contribution (essentially the d levels). By using this model, we obtained a quantitatively correct description of the top of the valence band and the lowest two conduction bands both in terms of energetic positions and band curvatures. In particular, the k.p Hamiltonian parameters are adjusted such that the transverse mass of the germanium conduction band is equal to the experimental value of 0.081.

The solution of the kinetic equation for phonon heat conductivity by the method of momenta and the influence of isotopic disorder on phonon heat conductivity of germanium and silicon crystals at T=300 K

The problem of solving the kinetic equation for the heat conductivities of dielectric substances and semiconductors by the method of momenta is discussed. Microscopic models are used to estimate the effect of isotopic disorder on the thermal resistance of germanium crystals in the multimomentum approximation. The contributions of acoustic and optical phonons are taken into account. Excess thermal resistance ΔW of samples with a natural isotopic composition compared with highly enriched samples is calculated. For germanium, the theoretical and experimental Δ W values are in close agreement with each other. For silicon, the theoretical ΔWvalue is much smaller than its experimental excess thermal resistance.

Study of structural and electrical properties of germanium-doped indium oxide ceramics

This work is an experimental study of the effects of germanium doping on the structural and electrical properties of indium oxide ceramics. The samples were prepared using the solid state reaction between appropriate mixtures of indium oxide (In 2O 3) and germanium oxide (GeO 2). The chemical nature of the compounds was investigated by X-ray diffraction. Electrical measurements showed that the electrical conductivity increases appreciably with the addition of germanium. Varying the composition of the ceramics allows to show that an increase by a factor of about 1.5 of the conductivity of germanium- doped indium oxide ceramics can be obtained.

Influence of annealing on the dislocation-related electrical conductivity of germanium

Germanium n-type single crystals with a donor concentration of 3×1012 cm−3 were deformed at 760°C to strains of δ≤71% with a rate of 6×10−3 s−1, cooled to room temperature, and then annealed for t≤20 h at 900°C. Low-temperature static electrical conductivity due to holes trapped by dislocations and transported along a branching dislocation network was measured before and after annealing of the deformed samples. It was found that annealing enhances the dislocation-related electrical conductivity in the samples with δ 60%. Selective etching and X-ray diffraction analysis showed that the main structural distinction of the samples with δ>60% is the presence of recrystallized regions. The influence of annealing on dislocation-related electrical conductivity is explained by an increase in connectedness of the dislocation network for δ 60%.

Effect of isotopic disorder on the thermal conductivity of germanium in the region of the maximum

This paper discusses the question of how isotopic disorder affects the position of the thermal-conductivity maximum of germanium. The discussion is in terms of a Callaway-type model. Experimental data on the thermal conductivity of a natural Ge crystal and of highly enriched Ge70 crystals are analyzed.

Electrical conductivity of germanium with dislocation grids

Samples of n-type germanium with a donor concentration Nd=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.