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Heavily p-type doped Ge layers were fabricated by 100 keV Ga implantation and subsequent flash lamp annealing for 3 ms in the temperature range between 700 and 900 °C. For comparison, some samples were annealed in a rapid thermal processor for 60 s. Ga fluences of 2×1015, 6×1015, and 2×1016 cm-2 were chosen in order to achieve Ga peak concentrations ranging from values slightly below the equilibrium solid solubility limit of 4.9×1020 cm-3 up to 3.5×1021 cm-3 which corresponds to a maximum Ga content of about 8 at. %. The structure of the doped layer and the Ga distribution were investigated by Rutherford backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy, and secondary ion mass spectrometry. Temperature dependent Hall effect measurements were carried out in order to determine the electrical properties of the Ga-doped Ge layers. It is shown that by flash lamp annealing Ga diffusion into the bulk can be completely avoided and the Ga loss by outdiffusion from the surface is reduced. The lowest sheet resistance of 36 Ω/sq. was achieved for the medium Ga concentration annealed at 900 °C. The best Ga activation values are 73%, 60%, and 24% for the three Ga fluences under investigation. The Ga activation is correlated with the layer regrowth. Incomplete epitaxial regrowth as observed in some samples leads to lower activation. [ABSTRACT FROM AUTHOR]

Si films sputter deposited on thermally oxidized Si are enriched with Ga by ion implantation through a SiO2 capping layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga-rich nanoinclusions are embedded in a nanocrystalline Si matrix. The metallic nanoinclusions become superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga-rich Si films show a wealth of low-temperature transport phenomena, which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance. The possibility to prepare and modify Ga-rich Si films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [ABSTRACT FROM AUTHOR]

Superconducting layers in silicon and germanium are fabricated via gallium implantation through a thin SiO2 cover layer and subsequent rapid thermal annealing. Gallium accumulation at the SiO2/Si and SiO2/Ge interfaces is observed but no pure gallium phases were found. In both cases superconducting transition occurs around 6-7 K which can be attributed to the metallic conducting, gallium rich interface layer. However, the superconducting as well as the normal-state transport properties in gallium overdoped silicon or germanium are different. [ABSTRACT FROM AUTHOR]

We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at. %. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channeling, secondary-ion-mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·1020 to 5.3·1020 cm-3 (0.4 to 1.2 at. %) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at. %. Higher concentrations lead to an increase of Tc from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m2 point to a large impact of the microstructure. [ABSTRACT FROM AUTHOR]

Ga-rich layers in Si were fabricated by 80 keV Ga implantation through a 30 nm SiO2 cover layer and subsequent rapid thermal annealing for 60 s in a temperature range between 500 °C and 1000 °C. Fluences of 2x1016 cm-2 and 4x1016 cm-2, leading to Ga peak concentrations of 8 at. % and 16 at. %, are chosen. Residual damage in the implanted layers and the Ga distribution were investigated by Rutherford-backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy, and x-ray photoelectron spectroscopy. Temperature-dependent Hall-effect measurements were carried out in order to determine the electrical properties of the implanted layers. It is shown that annealing at temperatures up to 800 °C leads to the formation of polycrystalline layers containing random distributed amorphous clusters. At the Si/SiO2 interface a dense and narrow band of Ga-rich clusters is observed. For 4 x 1016 cm-2 the amount of mobile Ga is higher than for 2x1016 cm-2 and an increase of the cluster density at the Si/SiO2 interface was found. Due to the higher cluster density for 4x1016 cm-2 this interface layer can become superconducting below 7 K with critical fields exceeding 9 T at optimized annealing conditions. Critical currents are above 1 kA/cm² and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900 °C and above, the implanted layers are single crystalline and no amorphous precipitates were detected. [ABSTRACT FROM AUTHOR]

We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology. [ABSTRACT FROM AUTHOR]

Heavily Ga implanted Si nanolayers covered with a thin SiO2 layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states-the superconducting and the superinsulating one. There is a resistance criterion for the phase transition closely associated with a critical hole concentration. [ABSTRACT FROM AUTHOR]