Mobility enhancement of strained Si by optimized SiGe/Si/SiGe structures

An un-doped SiGe/strained Si/SiGe quantum well was fabricated on p-type Si at 550 °C by hot-wall ultrahigh vacuum chemical vapor deposition. To induce a two-dimensional electron gas (2DEG) in the strained Si channel, a gate structure with Al 2O 3 and Cr/Au metal was deposited and biased at positive bias. The 2DEG mobility reaches 2 × 10 6 cm 2/V s, a record value, at 0.3 K for 15 nm Si well with a 526 nm Si 0.86Ge 0.14 barrier layer. The dominant factors that limit the mobility are Coulomb scattering of background charges and interface roughness scattering. In addition, the threading dislocation scattering also plays a role to determine the peak mobility. Reduction of Ge concentration in the SiGe barrier layer and the relaxed buffer layer decreases the threading dislocation density and the roughness, effectively enhancing the mobility of the 2DEG in the Si channel. © 2012 American Institute of Physics.