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 (GeratioGa) 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 approximately 60 nm thick GeratioGa layer. The Cooper-pair density in GeratioGa appears to be exceptionally low.

Amorphization of 6H-SiC with 200 keV Ge+ ions at room temperature and subsequent ion-beam-induced epitaxial crystallization (IBIEC) with 300 keV Si+ ions at 480 °C have been studied by Rutherford backscattering spectrometry/channeling and transmission electron microscopy analysis. Experimental results on amorphous layer thicknesses have been compared with trim calculations in association with the critical energy density model. Density changes during amorphization have been observed by step height measurements. Particular attention has been directed to the crystal quality and a possible polytype transformation during the IBIEC regrowth. The IBIEC process consists of two stages and results in a multilayer structure. In the initial phase an epitaxial growth of 6H-SiC has been obtained. With increasing IBIEC dose the epitaxial growth changes to columnar growth and is stopped by polycrystallization of 3C polytype in the near-surface region.

The density of amorphous SiC layers formed by 2 MeV Si+ implantation into single-crystalline 6H–SiC was measured by x-ray reflectometry and compared with the results of step height measurements. Reactive ion etching was used to investigate the density as a function of depth. The density of the as-amorphized SiC is about 12% less than that of the crystalline material. Within experimental accuracy, the density reduction is homogeneous across the whole layer thickness. Low-temperature annealing leads to the formation of relaxed amorphous SiC with a density about 7% below the crystalline one. These large density changes are in contrast to results in amorphous Si. They can be explained by the high atomic density of SiC and the chemical disorder in the amorphous state of SiC.

No abstract

Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. In contrast to conventional annealing procedures an activation up to 6.5× 1019 cm-3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pretreatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters

The annealing behavior of amorphous SiC layers produced by MeV Si implantation into 6H–SiC has been investigated systematically by means of step height measurements, x-ray diffraction, and optical microscopy. Two annealing stages are found. Each of them causes a specific densification of the amorphous layer. At temperatures between 250 and 700 °C both the rapidity and the low activation energy (184 meV) of the densification suggest that defect annealing processes are responsible for densification. Partial crystallization and changes of the amorphous network structure can be excluded as a possible reason for low temperature densification. Annealing at temperatures above 700 °C is characterized by a combination of defect annealing and recrystallization. The crystallization kinetics is analyzed in terms of the Johnson–Mehl–Avrami theory. It is shown that the crystallization mode changes with increasing temperature from nucleated growth at 800 °C to epitaxial growth at 1000 °C. The recrystallization generates stress in the layer which leads to surface cracking if the layer exceeds a critical thickness.

No abstract

Ion-beam-induced recrystallization of amorphous surface layers on single-crystalline silicon carbide substrates (6H–SiC) has been investigated at temperatures of 500 and 1050 °C by cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry and channeling. It is shown, that ion irradiation substantially reduces the onset temperature of both the epitaxial layer regrowth and the random nucleation of crystalline grains. Two recrystallization regimes have been found. At 500 °C ion-beam-induced random nucleation (IBIRN) of crystalline grains strongly competes with ion-beam-induced epitaxial crystallization (IBIEC) and polycrystalline material stops the epitaxial regrowth front in an early stage. At a temperature of 1050 °C IBIEC dominates over IBIRN and a complete, but disturbed epitaxial regrowth is obtained.