Hello, I am doing my prep work for the 'Hall Effect' experiment that I will be doing next week in labs and have a question regarding the forbidden region between the valence band and the conduction band. I haven't taken any formal solid state physics, but this is 2nd year lab, if that helps. The description of band theory for conductors and insulators is easy to understand, with the fermi level being in the conduction band for conductors, allowing electrons to be in the conduction band when in the ground state, and the fermi level being in the valence band for insulators. The energy gap between the conduction and valence band is small for semiconductors, which makes their properties highly temperature dependent. We dope the material in order to make it more useful. N-Type Extrinsic semiconductors are doped with donor impurities that contribute electron energy levels high in the band gap and shifts the fermi level. It is now easy to elevate these electrons into the conduction band with an applied voltage, but I thought this 'band gap' was the forbidden region. What is missing/wrong with this understanding?