Experimental investigation of two-dimensional In-Ge thin films (original) (raw)
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Superconductivity in thin-film germanium in the temperature regime around 1 K
Superconductor Science and Technology, 2010
We report recent discoveries of superconductivity in p-type-doped germanium which has been fabricated by implantation of gallium ions into near-intrinsic cubic Ge. Depending on the detailed preparation and annealing conditions, we demonstrate that superconductivity can be generated and tailored in thin p-doped layers of the Ge host. By carefully adjusting the annealing parameters, we have been able to raise the onset temperature of superconductivity to about 1.4 K at a Ga peak concentration of ∼10 at.%. This progress and the large in-plane critical magnetic field of about the size of the Chandrasekhar-Clogston limit makes thin-film Ga-doped Ge (Ge:Ga) even more attractive for technological applications. There might be particular interest to utilize on-chip thin-film superconductivity in a semiconducting environment as our preparation method of Ge:Ga is fully compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining 'islands of the periodic table of elements' on which superconductivity has not been found so far.
Journal of Physics C Solid State Physics, 1985
We have investigated the effects of inhomogeneity on the magnetoresistance (MR) of thin mixture films of In-Ge. By performing these measurements near the superconducting transition temperature, we could identify the ghosr criticalfield. Ha. We have used the data on MR and H,*, to calculate quantities such as the coefficient of diffusion and the inelastic scattering time. A homogeneous-inhomogeneous transition is observed when the relevant length scale (the inelastic diffusion length or the superconducting coherence length) becomes of the order of the inhomogeneity scale in the sample.
Physical Review B, 2012
We studied the effect of magnetic doping with Gd atoms on the superconducting properties of amorphous Mo70Ge30 films. We observed that in uniform films deposited on amorphous Ge, the pair-breaking strength per impurity strongly decreases with film thickness initially and saturates at a finite value in films with thickness below the spin-orbit scattering length. The variation is likely caused by surface-induced magnetic anisotropy and is consistent with the fermionic mechanism of superconductivity suppression. In thin films deposited on SiN the pair-breaking strength becomes zero. Possible reasons for this anomalous response are discussed. The morphological distinctions between the films of the two types were identified using atomic force microscopy with a carbon nanotube tip.
Growth and melting behaviour of thin in films on Ge(100)
Applied Physics A Solids and Surfaces, 1991
Growth and melting behaviour of thin indium films on Ge(100) have been investigated by Auger-electron spectroscopy (AES), atomic force microscopy (AFM) and perturbed 77 angular correlation (PAC) spectroscopy, respectively. At room temperature indium is found to grow in three-dimensional islands even at submonolayer coverages. A very rough film surface is observed for thicknesses up to 230 ML. The melting behaviour of such films has been studied by PAC. A reduction of the melting temperature Tm as well as a strong supercooling of the films is observed. The electric field gradient for lilln(ulCd) in the indium islands is determined as a function of temperature and is used to monitor the local crystalline order of the films up to temperatures just below the melting point.
We present the investigation of conductance and magnetoresistance mechanism of Ge-on-GaAs films used for low-temperature resistance thermometers. At temperature below 10 K the main mechanism of conductivity in Ge films is the variable-range hopping. At low temperatures the magnetoresistance can be negative, and its magnitude increases with decreasing temperature. A new giant negative magnetoresistance effect in Ge films at ultralow temperature (T < 0.2 K) and low magnetic fields (H < 1 T) has been observed. This effect is very sensitive to temperature. At 0.03 K the Ge film resistance decreases up to 100 times for H = 1 Tesla. The effect saturates for fields above 1 Tesla. We discuss the physics of this phenomenon and present the results of calculation using a development of the hopping theory of conductivity with the localization corrections.
Superconducting State in a Gallium-Doped Germanium Layer at Low Temperatures
Physical Review Letters, 2009
We demonstrate that the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure. Using advanced doping and annealing techniques of state-of-the-art semiconductor processing, we have fabricated a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the $60 nm thick Ge:Ga layer. The Cooper-pair density in Ge:Ga appears to be exceptionally low.
Large negative magnetoresistance in Ge films at ultralow temperatures and low magnetic fields
Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resistance thermometers, at temperatures below 0.2 K and magnetic fields below 1 T. This effect is very sensitive to temperature. At T 0.3 K, the magnetoresistance is negative, and its magnitude increases with decreasing temperature. At 0.03 K, the resistance strongly decreases up to 100 times when the magnetic field is increased from 0 to 1 T and then saturates in higher fields. We discuss the mechanisms of this phenomenon and present results of calculations involving the hopping theory of conductivity with localization corrections.
High positive magnetoresistance in Ge films at low temperatures
High positive magnetoresistance is found and investigated in p-Ge films on GaAs at low temperatures (1.4–4.2 K) and in magnetic fields up to 14 T. The film resistance grows exponentially with magnetic field. At a temperature of 1.4K and in a magnetic field of 14 T, the film resistance is increased by a factor of 3.8. The magnetoresistance also grows exponentially as temperature is reduced. The Mott variable-range hopping conduction is observed in the films studied in the 1.4–21K temperature range. It is shown that experimentally observed magnetoresistance agrees well with the theory of compression of wave functions of the localized states in the plane normal to magnetic field. This results in reduction of their overlapping, decrease of electron tunneling probability, and consequently, considerable growth of film resistance. Based on experimental resistance dependences on temperature and magnetic field, the parameters of hopping resistivity in Ge films on GaAs are determined. A possibility of transition to interference effects in conduction leading to localization of charge carriers and negative magnetoresistance at temperature decrease is also discussed. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4973494\]