I try to understand why, really, there is no current (except for leakage) when a diode is reverse-biased. I studied several texts, and noone really explains, like for instance this otherwise very pedagogic Wikipedia article. How I think: The negative terminal connected to the p-region ought to attract the holes there (in other words, when holes are flowing one way, electrons flow the other way, from the negative terminal to the junction). On the other side of the diode, the positive terminal connected to the n-region attracts electrons, so electrons are flowing from the junction to the positive terminal. All in all, this would mean a current is flowing from one end of the diode to the other. This seems for me to be perfectly symmetrical to what happens when the diode is forward-biased - in the above paragraph, negative terminal becomes positive terminal and vice versa, and attraction becomes repulsion. I must be missing some of the physics... Please help someone!