Very thin SiGe relaxed buffer layers whose Ge composition was higher than 40% were fabricated by utilizing ion implantation method. Strain relaxation ratio of 70% with respect to Si was obtained. Rms roughness of the sample with Si+ implantation was only 0.45 nm in spite of high Ge composition and was much smaller than that of the sample without ion implantation. It was confirmed by cross-sectional transmission electron microscope (XTEM) observation that few threading dislocations existed in the Si0.53Ge0.47 layer. P-type modulation doped strained Ge channel structure formed on the Si0.53Ge0.47 buffer showed hole Hall mobilities as high as 16500 and 1450 cm2/(V s) at low and room temperatures, respectively. These results indicate that ion implantation method is promising for realization of high-performance strained channel heterostructure devices based on high Ge composition SiGe substrates.
The effects of gate bias on hole effective mass (m*) and Hall mobility were studied in strained-Ge channel modulation-doped structures. Shubnikov–de Haas oscillations were analyzed with and without the bias and a significant m* increase from 0.15 to 0.22 m0 was observed with the increase in the carrier density due to the strong nonparabolicity of the valence band. This is a clear demonstration that modification of carrier density via gating considerably affects m*, which may have critical effects on device properties. The gate bias dependence of Hall mobility was also investigated and the dominant scattering mechanism was clarified in various temperature and carrier density regions.
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