On Effects of Gate Bias on Hole Effective Mass and Mobility in Strained-Ge Channel Structures

Abstract

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.

Strain Distribution Analysis of Sputter-Formed Strained Si by Tip-Enhanced Raman Spectroscopy

“…Biaxial global-strain-type strained Si (s-Si) formed on a Si 1Àx Ge x strain-relief relaxed buffer has been intensively applied to high-electronmobility transistors such as modulation-doped field-effect and metal-oxide-semiconductor transistors. [1][2][3][4][5] However, when we form global-strain-type s-Si by currently used gas-source methods such as gas-source molecular beam epitaxy (GS-MBE) and chemical vapor deposition (CVD), a crosshatch undulation pattern is generally formed on the surface with an undulation pitch of typically less than 1 m. 6) This surface undulation causes a nonuniform strain distribution 7) and variations in the physical properties and device performance on the surface. This is a serious issue to be solved for smaller and higher-density devices.…”