Calculations of hole mass in [110]-uniaxially strained silicon for the stress-engineering of p-MOS transistors

摘要

The influence of stress on transport properties in p-MOSFETs is rather well known for the case of biaxially strained channels obtained using hetero-epitaxy. However, results concerning biaxial stress do not apply for other stress configurations. For the stress-engineering of sub-45 nm devices, simplified models of the valence-band structure are required, which can predict the variation of their electrical performances for any stress configuration and channel orientation. In this work, we use the analytical formulation of a 6 x 6 k.p strained Hamiltonian to derive transport parameters for holes in the cases of both tensile and compressive (001)-biaxial and [110]-uniaxial stress. The model is first validated for the well-known cases of unstrained and (001)-biaxially strained silicon: our calculations are found to be in strong agreement with previous results obtained using more intensive computations. Then the variations of the different transport parameters for holes (energy splitting, density of states effective mass, and directional mass) as a function of [110]-uniaxial stress are provided in the energy range 0-55 rneV. In particular, we show that the stress-induced changes of the longitudinal hole mass along the channel of p-MOSFETs are consistent with the trends recently observed for the mobility variations in strained devices. These variations of hole mass can be used as a guide for the stress-engineering of the future generations of process-induced strained transistors.