I have been studying band theory and semiconductors in condensed matter physics and I am confused about the relation between mobility and velocity of electrons and holes in semiconductors.
My standard text book reference, Introduction to Solid State Physics, by Charles Kittel, says this:
i.e., the velocities of electrons and holes are the same in a semiconductor.
However, I was also reading about the dependence of the Hall coefficient on temperature and found this:
Now I can't understand how the mobilities of electrons and holes are different if their velocities are the same. What am I missing here?
Also, intuitively why should the mobilities be different for electrons and holes? Does it depend on doping too? Holes are just the gaps left behind by electrons and can practically be regarded as positive versions of electrons. Is it due to the mass factor coming into play due to electrons having some mass but holes being massless? Even then, holes should be more mobile than the electrons, right?