In this paper, a high-quality sputtered-GeSn layer on Ge (100) with a Sn composition up to 7% was demonstrated. The crystallinity of the GeSn layer was investigated via high-resolution X-ray diffraction (HR-XRD) and the strain relaxation degree of the GeSn layer was evaluated to be approximately 50%. A novel method was also proposed to evaluate the averaged threading dislocation densities (TDDs) in the GeSn layer, which was obtained from the rocking curve of GeSn layer along the (004) plane. The photoluminescence (PL) measurement result shows the significant optical emission (1870 nm) from the deposited high-quality GeSn layer. To verify whether our deposited GeSn can be used for optoelectronic devices, we fabricated the simple vertical p-i-n diode, and the room temperature current–voltage (I–V) characteristic was obtained. Our work paves the way for future sputtered-GeSn optimization, which is critical for optoelectronic applications.

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Germanium-tin films with rather high Sn content (28.04% and 29.61%) are deposited directly on Si (100) and Si (111) substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge 1−x Sn x films is investigated by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The x-ray diffraction (XRD) is also performed to determine the crystallinities of the Ge 1−x Sn x films. The experimental results indicate that root mean square (RMS) values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400 • C. The diameter of the Sn three-dimensional (3D) island becomes larger than that of an as-grown sample when the annealing temperature is 700 • C. In addition, the Sn surface composition decreases when annealing temperature ranges from 400 • C to 700 • C. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600 • C. The present investigation demonstrates that the crystallinity of Ge 1−x Sn x /Si (111) has no obvious advantage over that of Ge 1−x Sn x /Si (100) and the selection of Si (111) substrate is an effective method to improve the surface morphologies of Ge 1−x Sn x films. We also find that more severe Sn surface segregation occurs in the Ge 1−x Sn x /Si (111) sample during annealing than in the Ge 1−x Sn x /Si (100) sample.

The analysis of threading dislocation density (TDD) in Ge-on-Si layer is critical for developing lasers, light emitting diodes (LEDs), photodetectors (PDs), modulators, waveguides, metal oxide semiconductor field effect transistors (MOS-FETs) , and also the integration of Si-based monolithic photonics. The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope (TEM). However, high-resolution x-ray diffraction (HR-XRD) rocking curve provides an optional method to analyze the TDD in Ge layer. The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors. In this paper, this method is extended to the case of strained Ge-on-Si layers. The HR-XRD 2θ /ω scan is measured and Ge (004) single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer. The rocking curve full width at half maximum (FWHM) broadening by incident beam divergence of the instrument, crystal size, and curvature of the crystal specimen is subtracted. The TDDs of samples A and B are calculated to be 1.41×10 8 cm −2 and 6.47×10 8 cm −2 , respectively. In addition, we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.

To visualize the relationship between the collector current and source-drain voltage in the SiGe/Si chare injection transistor (CHINT), the mathematical model of this device is set up by using the tunnel model of two-dimensional hole gas(2DHG)in SiGe/Si quantum well. Then the model is simulated by MATLAB, the result shows that the drain current shows strong negative differential resistance when VDS is about 1.5V, which is in accordance with the results of the other papers.