Valence Subband Structures and Hole Effective Masses of PMOS Inversion Layer in Uniaxial Strained (110) and (111) Silicon Channel

Valence subband structures and hole effective masses of PMOS inversion layer in uniaxial strained Si channel on (110) and (111) Si substrates are studied theoretically based on the 6-band k.p model. The channel direction is chosen as along the 45º direction in the x-y plane, namely, [-1 1 -√2] in the (110) system and [1-√3 1+√3 -2] in the (111) system. Uniaxial stresses considered are applied in the directions parallel and perpendicular to the channel, respectively. Both compressive and tensile strains are considered, which can be realized by doping carbon or germanium into the opposite sides of the Si channel. Energy dispersions, constant-energy-contours, carrier-concentration effective mass, mc, and conductivity effective mass, mσ, of the three lowest subbands are calculated as functions of the applied stress under gate bias of 1 MV/cm. Our results show that the conductivity effective mass of the (110) system is in general lower than that of the (111) system, but in either (110) or (111) system, it is lowered by the compressive stresses applied in the direction parallel to the channel or the tensile stresses applied in the direction perpendicular to the channel.