What prevents the lead attached to a semiconductor from forming Shottky junction

There is usually an intermediary material between the semiconductor and the lead wires that does not form a Schottky barrier.

Either the metal-side material is chosen so that the resultant potential energy barrier at the junction is low enough that it doesn't significantly impede the flow of charge carriers or the semiconductor near the junction is so highly doped that the barrier is thin enough that charge carriers can tunnel through it.