Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader

1. Lecture 3 Semiconductors at equilibrium (2) Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader By: Dr Tarek Abdolkader

2. OUTLINE • Doping and extrinsic semiconductor • Donor doping • Acceptor doping • Carrier concentrations • Position of the Fermi level Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

3. Doping and extrinsic semiconductor • 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. Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

4. Donor doping • n-type doping (Donor doping): e e SILICON DOPED WITH DONORS at zero temperature SILICON DOPED WITH DONORS at room temperature PURE SILICON CRYSTAL • Consider adding a GROUP Velement 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. Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

5. Donor doping • n-type doping (Donor doping): Ec Donor level e Ev zero temperature Low temperature room temperature SILICON DOPED WITH DONORS AT ROOM TEMPERATURE • 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 majoritycarriers and holes as minority carriers. Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

6. Donor doping • n-type doping (Donor doping): zero temperature high temperature room temperature Low temperature Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Variation of the Fermi level with temperature for both n-type and p-type semiconductor Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

7. Acceptor doping h • p-type doping (Acceptor doping): h Silicon doped with acceptors at zero temperature Silicon doped with acceptors at room temperature PURE SILICON CRYSTAL • Consider adding a GROUP III element of the periodic table (with threevalence 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. Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader

8. Acceptor doping h • p-type doping (Acceptor doping): Ec Acceptor level Ev Silicon doped with acceptors at room temperature zero temperature Low temperature room temperature • 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-typesemiconductor). • We call holes as majoritycarriers and electrons as minority carriers. Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Dr Tarek Abdolkader Electronic devices (802311) Lecture 3 Dr Tarek Abdolkader