We review the technology of Ge1−xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1−xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1−xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1−xSnx, and insulators/Ge1−xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1−xSnx-related materials, as well as the reported performances of electronic devices using Ge1−xSnx related materials.

We synthesized carbon nanowalls (CNWs) using radical injection plasma-enhanced chemical vapor deposition. The initial growth process of CNWs was investigated with and without O2 gas addition to a C2F6 capacitively coupled plasma with H radical injection. In the case of the CNW synthesis without the addition of O2 gas, scanning electron microscopy (SEM), transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that a 10-nm-thick interface layer composed of nanoislands was formed on a Si substrate approximately 1 min prior to CNW formation. In contrast, with O2 gas addition, SEM and XPS revealed that an interface layer was not formed and that CNWs were grown directly from nanoislands. Moreover, Raman spectroscopy suggested that the interface layer was composed of amorphous carbon and that O2 gas addition during CNW growth is effective for achieving a high graphitization of CNWs. Therefore, O2 gas addition has the effect of reducing the amorphicity and disorder of CNWs and controlling CNW nucleation.

The electrical conduction behavior of carbon nanowalls (CNWs) has been evaluated by Hall measurement. CNWs, which comprise stacks of graphene sheets standing on the substrate, are fabricated by fluorocarbon/hydrogen plasma enhanced chemical vapor deposition. We have investigated the effect of N2 addition to C2F6∕H2 system on the electrical properties of CNWs. The CNWs grown with the C2F6∕H2 plasma exhibit p-type conduction. As a result of the nitrogen inclusion in the CNWs, the conduction type of the CNWs changes to n type. The carrier concentration is controllable by changing the flow rate of the additional N2 during the CNW growth process.

We investigated the effects of incorporation of 0%–2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1−xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1−xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20–30 nm. The Hall hole mobility of a poly-Ge1−xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

This study describes the development of a compact measurement technique for absolute carbon (C) atom density in processing plasmas, using vacuum ultraviolet absorption spectroscopy (VUVAS) employing a high-pressure CO2 microdischarge hollow-cathode lamp (C-MHCL) as the light source. The characteristics of the C-MHCL as a resonance line source of C atoms at 165.7 nm for VUVAS measurements of the absolute C atom density are reported. The emission line profile of the C-MHCL under typical operating conditions was estimated to be the Voigt profile with a ΔνL/ΔνD value of 2.5, where ΔνL is the Lorentz width and ΔνD is the Doppler width. In order to investigate the behavior of C and H atoms in the processing plasma used for the fabrication of two-dimensional nanographene sheet material, measurements of the atom densities were carried out using the VUVAS technique. The H atom density increased with increasing pressure, while the C atom density was almost constant at 5×1012 cm−3. The density ratio of C to H atoms in the plasma was found to influence the morphology of carbon nanowalls (CNWs). With increasing H/C density ratio, the growth rate decreased and the space between the walls of the CNWs became wider.

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We have fabricated carbon nanowalls (CNWs) composed of monolithic self‐sustaining nanographene sheets standing vertically on a Si substrate, using plasma‐enhanced chemical vapor deposition with a C2F6/H2 mixture. The crystallinity, evaluated by Raman spectroscopy and synchrotron X‐ray surface diffraction, and the electrical properties of the CNWs were improved by introducing O2 gas into the source gas mixture during the CNW growth process. The temperature dependence of the resistivity of the CNW films exhibited semiconductor behavior.

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