Determination of the free carrier concentration in atomic-layer doped germanium thin films by infrared spectroscopy

Novel silicon photonics applications requiring heavy n-type doping have recently driven a great deal of interest towards the phosphorous doping of germanium. In this work we report on infrared reflectance spectroscopy measurements of the electron density in heavily n-type doped germanium layers obtained by stacking multiple phosphorous δ-layers. Here, we demonstrate that the conventional Drude model of the electrodynamic response of free carriers in metals can be adapted to describe heavily doped semiconductor thin films. Consequently, the effect of the electron density on the plasma frequency, scattering rate and complex permittivity can be investigated.

Source:IOPscience

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Heat capacity of germanium crystals with various isotopic composition

The heat capacity of three pure (n, p≤2×1016 cm-3) germanium crystals with different isotopic compositions was measured in the temperature range from 2.8 K to 100 K. These samples, one made of enriched 70Ge (95.6%), Ge of natural isotopic composition and n, p < 1014 cm-3, and one of the largest possible isotopic mass variance 70/76Ge (43%/48%) with n, p<1014 cm-3, show a change of the molar heat capacity (and corresponding Debye temperature, θD) as expected from the average mass variation, corresponding to θD∝M-0.5 (M = molar mass) at low temperatures. The mass effect is best visible around 21.5 K, at the minimum of the corresponding Debye temperatures θD, and amounts to ΔθD = 5.3 K for the difference between the Debye temperatures of 70Ge and 70/76Ge. The specific heat capacity of the natural Ge crystal agrees within 2% with the best data available in the literature taken on much larger masses of Ge.

Source:IOPscience

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Thin germanium–carbon layers deposited directly on silicon for metal–oxide–semiconductor devices

We report the growth process and materials characterization of germanium–carbon alloys (Ge1−xCx) deposited directly on Si (1 0 0) substrates by ultra-high-vacuum chemical vapour deposition. The Ge1−xCx films are characterized by transmission electron microscopy, etch-pit density, x-ray diffraction, secondary ion mass spectrometry and electron energy loss spectroscopy. The results show that the films exhibit low threading dislocation densities despite significant strain relaxation. We also present evidence for carbon segregation in the Ge1−xCx and interpret these results as a strain relaxation mechanism.

Source:IOPscience

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New concept of planar germanium MOSFET with stacked germanide layers at source/drain

In this paper, we have proposed and simulated one novel Schottky barrier germanium-based MOSFET structure. Herein, the source/drain region of the device is consisted with two stacked layers of germanide materials. Different barrier heights of the top and bottom contact are hence formed with channel respectively. The top barrier height is designed lower enough to enlarge drive current, and the bottom barrier height is higher (nearly mid-gap) to diminish the leakage current. The working mechanism and the performance of n- and p-type devices is studied. Comparisons between dual barrier structure and single barrier structure are also carried out. The results show that the characteristics have been significantly enhanced with the proposed dual barrier structure. Besides, the devices' performance is nearly insensitive to germanium thickness, which leads to the relax of the requirement of germanium-on-insulator (GeOI) structures for leakage immunization.

Source:IOPscience

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