On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on
the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical conductivity
follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This
behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at
the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature TC, we
obtained the Mott Variable Range Hopping regime with T-1/4, indicating that the DOS becomes almost constant
in the vicinity of the Fermi level. The critical temperature TC decreases with nickel content in the alloys.
Longitudinal and positive magnetoresistance behaviour was used to determine what of the Variable Range Hopping (VRH) conduction regime is found in insulating InSb sample, Mott VRH regime or Efros- Shklovskii (ES) VRH regime. Experimental results are reported on field longitudinal magnetoresistance in insulating n-type InSb sample in which range hopping occurs at low temperatures. Positive magnetoresistance associated with VRH conduction has been observed. Experimental data are tentatively compared with available theoretical models in the insulating regime.
We present results of an experimental study of magnetoresistance (MR) in insulating NbSi amorphous alloys
sample showing Variable Range Hopping (VRH) conductivity ; The MR is found to be negative in a wide range
of low temperature (4.2-20 K) and in the range of moderate magnetic fields (0-4 T). We made tentative analysis
using three theoretical models which are the model of quantum interference, the model of Zeeman effect and the
model of localized magnetic moments.
We present measurements of the electrical conductivity of barely metallic n-type GeSb that are driven to the metal-insulator transition (MIT) by impurity concentration. The experiments were carried out at low temperature in the range (4.2 -0.066 K) and with impurity concentrations up 6.41017 cm−3 . On the metallic side of the MIT, the electrical conductivity is found to behave like σ =σ0 + mT1/2 down to 66 mK. Physical explanation to the temperature dependence of the conductivity is given in metallic side of the MIT using a competition between two effects involved in the mechanisms of conduction, like electron-electron interaction effect, and weak localization effect.
We present results of an experimental study of magnetoresistance phenomenon in an amorphous siliconnickel
alloys a-Si1-yNiy:H (where y=0.23) on the insulating side of the metal-insulator transition (MIT) in
presence of magnetic field up to 4,5T and at very low temperature. The electrical resistivity is found to
follow the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T -1/2. This behaviour
indicates the existence of the Coulomb gap (CG) near the Fermi level.
The metal-insulator transition (MIT) induced by magnetic field, in barely metallic
and compensated n-type GaAs has been analyzed using a scale theory. The experiments were
carried out at low temperature in the range (4.2 -0.066 K) and in magnetic field up to 4 T. We
have determined the magnetic field for which the conductivity changes from the metallic
behaviour to insulator regime. On the metallic side of the MIT, the electrical conductivity is
found to obey σ = σ + mT1/2 down to 66 mK. The zero-temperature conductivity can be described by scaling laws.
We report here carrier's magneto-transport properties and the band structure results for II-IV semiconductors. HgTe is a
zero gap semiconductor when it is sandwiched between CdTe layers to yield to a small gap HgTe/CdTe superlattice
which is the key of an infrared detector. Our sample, grown by MBE, had a period d (100 layers) of 18 nm (HgTe) / 4.4
nm (CdTe). Calculations of the spectra of energy E(kz) and E(kp), respectively, in the direction of growth and in the
plane of the superlattice were performed in the envelope function formalism. The angular dependence of the transverse
magnetoresistance follows the two-dimensional (2D) behavior with Shubnikov-de Haas oscillations. At low temperature,
the sample exhibits p type conductivity with a hole mobility of 900 cm2/V.s. A reversal the sign of the weak-field Hall
coefficient occurs at 25 K with an electron mobility of 3.104 cm2/Vs. In intrinsic regim, the measured Eg ≈ 38 meV
agrees with calculated Eg(Γ,300 K) = 34 meV which coincide with the Fermi level energy. The formalism used here
predicts that this narrow gap sample is semi metallic,
quasi-two-dimensional and far-infrared detector.
We present magnetoresistance measurements on metallic n-type InP sample with a carrier density n=1.241023m-3, far from the metal-insulator transition (MIT). The experiments were carried out at low
temperature in the range 4.2-0.6 K and in magnetic fields up to 1 T. We have observed negative magnetoresistance (NMR) behaviour, and the experimental data are interpreted in terms of the weak localization
and the effect of electron-electron interactions. Experimental data are compared with available theoretical
models using a non-linear regression method with adjustable parameters τε and F. τε is the inelastic scattering time and F is the Hartree-Fock constant.
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