By means of a tight-binding approach, we have studied the influence of
barrier states on the conduction band of the T-and V-shaped quantum w
ires. For AlAs/GaAs superlattices or pure AlAs barriers, X-related sta
tes induce strong modifications in the wire conduction band that canno
t be accounted For by a simple effective-mass approximation. With resp
ect to quantum wells, we show that the quasi-one-dimensional confineme
nt of quantum wires enhances valley mixing and leads to a reduction in
the energy of lower lying states.