Si/Si 1−x Ge x heterostructures: Electron transport and field-effect transistor operation using Monte Carlo simulation

Using an ensemble Monte Carlo simulation, we study the electron transport properties in tensile strained Si grown on a Si1−xGex substrate and in an n-channel Si/Si1−xGex modulation-doped field-effect transistor (MODFET). Owing to the strain-induced modification of the conduction-band structure, the in-plane drift mobility in undoped material reaches 3250 cm2/V s at 300 K (for x⩾0.2) and 31000 cm2/V s at 77 K (for x⩾0.05). The two-dimensional Monte Carlo modeling of 0.18 μm gate Si/SiGe MODFETs reveals a high velocity overshoot of 2.5×107 cm/s related to a significant ballistic transport through the gated part of the strained Si channel. For a 0.18 μm gate and a Ge mole fraction x=0.3, intrinsic transconductance and transition frequency as high as 460 mS/mm and 85 GHz are obtained.