I'm reading up on semiconductors and there seems to be a few fundamentals I cannot find answers for if anyone can help? I understand that n-type substrate is doped with a donor and p-type substrate is doped with an acceptor creating excess electrons and holes. When you put the p-type and n-type together you get a diode with a depletion layer. My problem comes with radiation detectors. In the paper below it states that a p-type diode (not substrate) is when you dope small amounts of donor impurities into a p-type substrate. Also a n-type diode (not substrate) is when you dope small amounts of acceptor impurities into a p-type substrate. Why dope the n-type with the opposite (p-type) donor? Is this not just undoing the original doping? So if this is right, you dope the n-portion of a p-n junction with the opposite doping (acceptors) to form an N-type diode? Paper: "Modeling the instantaneous dose rate dependance of radiation diode detectors" Jie Shie and William E. Simon Med. Phys 30(9), Sept 2003 Please clarify! Any help is appreciated!