Hi, I have a quick question. When constructing a semiconductor diode, the P-N junction is used to create a depletion region (depleted of mobile majority carriers) which is the active volume of the diode/detector. The region enables an electric current generated from the incomming radiation to be measured, due to the fact that the majority carriers are removed (they contribute to a current of order 0.1A, and radiation induced current is like 0.00001A). My question is, is the P-N junction the only means to acheive a depletion region? E.g if I took a (100%) pure crystal and applied a bias voltage to sweep away the electrons that were thermally excited, I would remove the majority carriers just like in the P-N junction. Does this statement fail to hold only due to the fact that there is no 100% pure crystal? And that any small amount of impurities drastically alters the crystals properties? Or is there another reason? Thank you for your time!