Evaluation of an equivalent hole effective mass for Si/SiGe structures

We have studied the carrier profile and calculated a unique effective mass for a two-dimensional hole gas confined in a SiO/sub 2//Si/Si/sub 1-x/Ge/sub x//Si structure when an external voltage is applied. For this purpose, we solved the system of differential equations provided by the 6/spl times/6 Luttinger Hamiltonian simultaneously with the Poisson equation, applying an iterative process until convergence was achieved. This enabled us to incorporate the warping and the strong coupling among the subbands that constitute the band structure. Although our calculations indicate that the effective mass changes slightly with the hole confinement level, in general, we have observed a decrease of the calculated effective mass as the molar fraction of Ge increases, which might justify the use of this kind of device. Nevertheless accuracy can only be obtained with a complete model as we have implemented by solving the whole Luttinger Hamiltonian.