Doesn't it seem odd that the current in p type is within the covalent band while the n type current is in the conduction band. I would suspect a property difference in there somewhere. Copper has overlapping energy bands whereas it takes the same amount of energy to push an electron in the conduction band as in the covalent band. Does anybody know what the real meaning of this phenomenon is? Did you know that they are using n type silicon nails now for ICT. As if they can really be worried about that inductance.
While we're on the subject, it's also worth mentioning that atom with more electrons have lower energy levels than atoms with few electrons. This is because the core attraction of the protons pulls the electrons closer to the nucleus. This means that the required energy to push the electrons into a higher energy band is less.