Let us assume a direct semiconductor with parabolic band structure around the $\Gamma$ point (which is not bad for most semiconductors) in momentum ($k$) space. Now we excite it with light:
I encircled the start and end state in red. The shaded area resambles the photon energy with momentum $q$. So my question to this kind of situation is, is it possible to have an electron at exactly $k=0$? My concerns are, that this would mean, that the electron would have no kinetic energy when $E=\hbar^2k^2/2m_e$. That means, that the position has maximal uncertainty after Heisenberg. And that would mean that the electrons wave function would be extended into infinity. Since a semiconductor is typically smaller than infinity, this can't be possible.