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, st...

We have investigated the behaviors of the carrier mobility and concentration of the undoped Ge_1-xSn_xlayers epitaxially grown on silicon-on-insulator (SOI) substrates. Hall measurement revealed the conduction of holes excited from acceptor levels related to vacancy defects whose concentration was as high as 10¹⁸cm^-3in Ge_1-xSn_xlayers. The temperature dependences of the carrier mobility and concentration in the valence band was estimated by reducing the parallel conduction component in the impurity band. The incorporation of Sn at a content lower than 4.0% hardly degraded the hole mobility of heteroepitaxial Ge_1-xSn_xlayers. In contrast, the mobility of the Ge_1-xSn_xlayers was improved by reducing the carrier concentration of the Ge_1-xSn_xlayers by Sn incorporation compared with that of the Ge layer formed under the same growth and annealing conditions. This result suggests that the incorporation of Sn into Ge leads to reducing the hole concentration of the electrically active vacancy defects due to the formation of Sn-vacancy pairs.

Praseodymium silicate (Pr silicate) has been synthesized by molecular-beam deposition of ${\mathrm{Pr}}_2{\mathrm{O}}_3$ layers on Si(111) substrates and subsequent high-temperature postdeposition annealing at 1000 °C. This thermal treatment drastically changes the film texture from the crystalline ${\mathrm{Pr}}_2{\mathrm{O}}_3$ epitaxially grown on Si, into Pr silicate with completely amorphized structures, resulting from intermixing of Si from the substrate. It was found that the electrical characteristics of Pr silicate were critically dependent on the quality of the as-deposited ${\mathrm{Pr}}_2{\mathrm{O}}_3$ films. A typical dielectric constant and a leakage current density of Pr silicate grown under an optimal condition were, respectively, 19.7 and $3\times {10}^{-9}\mathrm{A}{\mathrm{cm}}^{-2}$ at +1 V relative to the flatband voltage for an equivalent oxide thickness of 1.9 nm. Using x-ray photoelectron spectroscopy, a valence-band offset at the Pr-silicate/Si(111) interface of 2.75 eV and a band gap of 6.50 eV were obtained. The large band gap and the highly symmetric band alignment account for the observed low leakage current density.