المملكة العربية السعودية وزارة التعليم العالي - جامعة أم القرى كلية الهندسة و العمارة الإسلامية قسم الهندسة الكهربائية ELECTRONIC DEVICES K INGDOM OF S AUDI A RABIA Ministry of Higher Education Umm Al-Qura University College of Engineering and Islamic Architecture Electrical Engineering Department Lecture 3 By: Dr Tarek Abdolkader

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader2 Doping and extrinsic semiconductor Donor doping Acceptor doping Carrier concentrations Position of the Fermi level

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader3 We can modify the electron and hole densities by the controlled addition of impurities known as dopants. The process of the controlled addition of impurities is called doping. Semiconductors that are doped are known as extrinsic semiconductors. While in intrinsic semiconductors are equal, in extrinsic semiconductors, the number of electrons and the number of holes are NOT equal.

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader4 n -type doping (Donor doping): Consider adding a GROUP V element of the periodic table (with five valence electrons) such as phosphorous or arsenic to silicon. Four of the valence electrons form the covalent bonding with one electron left. The extra electron is more loosely bound to the phosphorous atom than the other four covalent electrons. Now, each dopant atom donates extra electron, so, it is called donor atom, and this type of doping is called donor doping. PURE SILICON CRYSTAL SILICON DOPED WITH DONORS at zero temperature SILICON DOPED WITH DONORS at room temperature ee

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader5 Donor electrons need much less energy to go into the CB than covalent bond electrons, so, they are assumed to be in an energy level close to the CB. This energy level is called “ Donor level ”. Even at very low temperatures, the extra electron may escape from the atom and become free. There is no hole left behind when the extra electron leave the atom. In this case n > p ( n-type semiconductor). We call electrons as majority carriers and holes as minority carriers. SILICON DOPED WITH DONORS AT ROOM TEMPERATURE e EcEc EvEv Low temperature zero temperature room temperature n -type doping (Donor doping): Donor level

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader6 Low temperature zero temperature room temperature n -type doping (Donor doping): high temperature Variation of the Fermi level with temperature for both n-type and p-type semiconductor

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader7 p -type doping (Acceptor doping): Consider adding a GROUP III element of the periodic table (with three valence electrons) such as Gallium or Boron to silicon. Three of the valence electrons form the covalent bonding with one hole left. Filling this extra hole by an electron needs much less energy than making the electron free in the lattice. Now, each dopant atom accepts electron, so, it is called acceptor atom, and this type of doping is called acceptor doping. PURE SILICON CRYSTAL Silicon doped with acceptors at zero temperature Silicon doped with acceptors at room temperature h h

16/11/1433Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader8 Acceptor holes need much less energy to be filled by an electron from the VB than states in the CB, so, they are assumed to be in an energy level close to the VB. This energy level is called “ Acceptor level ” Even at very low temperatures, the extra hole may be filled by an electron from the VB and releasing a hole there. There is no electron associated with this hole production. In this case p > n ( p -type semiconductor). We call holes as majority carriers and electrons as minority carriers. EcEc EvEv Low temperature zero temperature room temperature Acceptor level h Silicon doped with acceptors at room temperature p -type doping (Acceptor doping):