Low-temperature synthesis of polycrystalline (poly-) Ge on insulators is a key technology to integrate Ge-CMOS into existing devices. However, Fermi level control in poly-Ge has been difficult because poly-Ge has remained naturally highly p-type due to its defect-induced acceptors. We investigated the formation of n-type poly-Ge (thickness: 100-500 nm) using the advanced solid-phase crystallization technique with Sb-doped densified precursors. Sb doping on the order of 10 20 cm À3 facilitated lateral growth rather than nucleation in Ge, resulting in large grains exceeding 15 lm at a low growth temperature (375 C). The subsequent heat treatment (500 C) provided the highest electron mobility (200 cm 2 /V s) and the lowest electron density (5 Â 10 17 cm À3) among n-type poly-Ge directly grown on insulators. These findings will provide a means for the monolithic integration of high-performance Ge-CMOS into Si-LSIs and flat-panel displays.
The grain size and hole mobility of polycrystalline Si1-xGex thin films formed on glass by solid-phase crystallization were significantly improved after preparing the amorphous precursors by heating the substrate. By just controlling the deposition temperature of the precursors (50-350 °C) for each SiGe composition, the grain size reached over 2 μm across the whole composition range. Reflecting the enlargement of the grain size, the hole mobility values were improved by approximately one order of magnitude. These values are comparable to those of single-crystal SiGe formed by Ge condensation and are the highest among SiGe on insulators synthesized at low temperature (<900 °C). The SiGe on insulator technology obtained in this study will greatly contribute to the development of SiGe-based electronic and optical devices.
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