Nitrogen and phosphorus are N-type dopants for diamond. Electron donors, also known as N-type dopants include elements from group VA of the periodic table: nitrogen, phosphorus, arsenic, and antimony. It is possible to increase the number of negative charge carriers within the semiconductor crystal lattice by doping with an electron donor like Phosphorus. Doping increases the conductivity of a semiconductor so that it is more comparable to metal than an insulator. The addition of the desired impurity to a semiconductor is known as doping.
Semiconductor material pure to 1 part in 10 billion, may have specific impurities added at approximately 1 part per 10 million to increase the number of carriers. Though, semiconductors must be refined to a high level of purity as a starting point prior to the addition of specific impurities.
Pure semiconductors, by themselves, are not particularly useful. Another way of stating this is that mobility is not the same for electrons and holes. However, both carriers do not necessarily move with the same velocity with the application of an external field. The number of electrons and holes in an intrinsic semiconductor are equal. This is opposite of metals, where resistance increases with temperature by increasing the collisions of electrons with the crystal lattice. Increasing temperature will increase the number of electrons and holes, decreasing the resistance. If an external electric field is applied to the semiconductor, the electrons and holes will conduct in opposite directions.
#ANTIMONY ELECTRONS FREE#
That is, the electron is free until it falls into a hole. The free electron and hole both contribute to conduction about the crystal lattice. This hole is not fixed to the lattice but, is free to move about. When the electron was freed, it left an empty spot with a positive charge in the crystal lattice known as a hole. This electron is free for conduction about the crystal lattice. Thermal energy may occasionally free an electron from the crystal lattice as in Figure above (b). (b) However, thermal energy can create few electron-hole pairs resulting in weak conduction. (a) An intrinsic semiconductor is an insulator having a complete electron shell. Thus, intrinsic, pure, semiconductors are relatively good insulators as compared to metals. Electrons are not free to move about the crystal lattice. All electrons of an atom are tied up in four covalent bonds, pairs of shared electrons. This is a flattened, easier to draw, version of Figure above. The figure below (a) shows four electrons in the valence shell of a semiconductor forming covalent bonds to four other atoms. Why might this be? To answer that question, we must look at the electron structure of such materials in Figure below. Impure, or dirty semiconductors are considerably more conductive, though not as good as metals. This is analogous to a grain of salt impurity in a railroad boxcar of sugar. To be useful in semiconductor applications, the intrinsic semiconductor (pure undoped semiconductor) must have no more than one impurity atom in 10 billion semiconductor atoms. Pure semiconductors are relatively good insulators as compared with metals, though not nearly as good as a true insulator like glass.
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