When a large number of atoms (1020 or more) are brought together to form a solid, the number of orbitals becomes exceedingly large. Conductivity Properties of the Elements 2.2. The band gap is a very important property of a semiconductor because it determines its color and conductivity. The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. In semiconductors, the band gap is small, allowing electrons to populate the conduction band. However, once each hole has wandered away into the lattice, one proton in the atom at the hole’s location will be “exposed” and no longer cancelled by an electron. A p-type (p for “positive”) semiconductor is created by adding a certain type of atom to the semiconductor in order to increase the number of free charge carriers. Crucial to the conductivity method is whether or not or not there ar electrons inside the conductivity band. Metals: Weak Covalent Bonding 1.2. A band gap is an energy range in a solid where no electron states can exist due to the quantization of energy. 10.5: Semiconductors- Band Gaps, Colors, Conductivity and Doping, [ "article:topic", "showtoc:no", "license:ccbysa" ], https://chem.libretexts.org/@app/auth/2/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FInorganic_Chemistry%2FBook%253A_Introduction_to_Inorganic_Chemistry%2F10%253A_Electronic_Properties_of_Materials_-_Superconductors_and_Semiconductors%2F10.05%253A_Semiconductors-_Band_Gaps_Colors_Conductivity_and_Doping, 10.4: Periodic Trends- Metals, Semiconductors, and Insulators, information contact us at info@libretexts.org, status page at https://status.libretexts.org, Early transition metal oxides and nitrides, especially those with d, Layered transition metal chalcogenides with d. Zincblende- and wurtzite-structure compounds of the p-block elements, especially those that are isoelectronic with Si or Ge, such as GaAs and CdTe. Electrical Conductivity of Semiconductor In semiconductor the valance band and conduction band are separated by a forbidden gap of sufficient width. The Fermi level of a doped semiconductor is a few tens of mV below the conduction band (n-type) or above the valence band (p-type). In crystalline Si, each atom has four valence electrons and makes four bonds to its neighbors. In solid-state physics, the energy gap or the band gap is an energy range between valence band and conduction band where electron states are forbidden. Have questions or comments? Semiconductors and insulators have a greater and greater energetic difference between the valence band and the conduction bands, requiring a larger applied voltage in order for electrons to flow. (1) Going down a group in the periodic table, the gap decreases: Egap (eV): 5.4 1.1 0.7 0.0. Sometimes, there can be both p- and n-type dopants in the same crystal, for example B and P impurities in a Si lattice, or cation and anion vacancies in a metal oxide lattice. The result is that one electron is missing from one of the four covalent bonds normally part of the silicon lattice. Visible light covers the range of approximately 390-700 nm, or 1.8-3.1 eV. When a conduction band electron drops down to recombine with a valence band hole, both are annihilated and energy is released. This behaviour can be better understood if one considers that the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons, though in other cases they can be ions or other positively charged species. A very large band gap is indicative of an insulator--since it takes a great deal of energy for the electron to "jump" from the valence band to the conduction band, there will not likely be any conductivity. For example, in III-V semiconductors such as gallium arsenide, silicon can be a donor when it substitutes for gallium or an acceptor when it replaces arsenic. The conductivity (σ) is the product of the number density of carriers (n or p), their charge (e), and their mobility (µ). In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. 6 that the mobility μ is given by: \[\mu = \frac{v_{drift}}{E} = \frac{e\tau}{m}\]. For example, Si can occupy both the Ga and As sites in GaAs, and the two substitutions compensate each other. CC licensed content, Specific attribution, http://en.wikipedia.org/wiki/Electrical_conductor, http://en.wikipedia.org/wiki/Electronic_band_structure, http://en.wiktionary.org/wiki/molecular_orbital, http://en.wikipedia.org/w/index.php?title=File:Isolator-metal.svg&page=1, http://en.wikipedia.org/wiki/P-type_semiconductor, http://en.wikipedia.org/wiki/Doping_(semiconductor), http://en.wikipedia.org/wiki/Semiconductor, http://en.wikipedia.org/wiki/N-type_semiconductor, http://en.wikibooks.org/wiki/Semiconductors/What_is_a_Semiconductor, http://en.wiktionary.org/wiki/semiconductor, http://en.wikibooks.org/w/index.php?title=File:P-doped_Si.svg&page=1, http://en.wikibooks.org/w/index.php?title=File:N-doped_Si.svg&page=1, http://en.wikibooks.org/wiki/Semiconductors/What_is_a_Semiconductor%23Extrinsic_Semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal latti…