Moldavian Journal of the Physical Sciences, Vol.1, N3, 2002 9 VALENCE SUBBAND STRUCTURE CALCULATIONS OF STRAINED Si1-xGex/Si QW

In this paper we illustrate how the strain modifies the valence band structure of a semiconductor heterostructure based on Si1-xGex semiconductor alloys by varying Ge mole fraction when considering the coupling between heavy hole (HH) and light hole (LH) bands. The formulation is based on the 4×4 Luttinger-Kohn Hamiltonian taking into account the strain according to Bir-Pikus theory and the envelope function approximation. Under the axial approximation the 4×4 Hamiltonian can be diagonalized into two 2×2 blocks neglecting the in-plane anisotropy without losing the essential physics of band mixing. We consider a strained-layer quantum well, assuming that the growing direction is along the z-axis and the strain caused by the lattice mismatch is entirely elastically accommodated in the quantum well. The numerical results for a strained Si1-xGex quantum well with different Ge mole fraction grown on an unstrained Si barrier layer are shown. Interesting valence band structure for compression case shows clearly the effects of strain on the quantized subbands and the effective masses of the carriers in the plane transverse to the growth axis, thus affecting their transport properties. I