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What Are N-Type Semiconductors?

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  • Written By: Geisha A. Legazpi
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 18 September 2016
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Negative (N)-type semiconductors are partially conducting and partially insulating materials that donate electrons in electronic devices. N-type semiconductors, like their positive (P)-type counterpart, are made from elements such as silicon and germanium. Together, N-type semiconductors and P-type semiconductors are the building blocks of modern semiconductor devices.

Valence electrons in the atomic model are electrons in the outermost shell of orbit. Silicon, for instance, has four electrons in the valence shell. This makes silicon a semiconductor, or partial conductor and partial insulator. Full conductors, such as copper and aluminum, have more electrons on the valence shell, resulting in easier mobility of electrons leading to high conductivity.

When preparing silicon for producing semiconductors, silicon dioxide is heated at super elevated temperatures in the absence of oxygen. Silicon dioxide is the common sand found almost everywhere. Special equipment that produces pure silicon and its extrinsic forms are the bulk of investment in semiconductor production.

Extrinsic semiconductors are pure semiconductors that have been doped with impurity elements, such as phosphorus or bronze, to have the electron donor or electron acceptor characteristic. When a four-valence electron element is doped with a five-valence electron element, N-type semiconductors result. Using a three-valence element results in a P-type semiconductor. The amount of impurity is about 1 impurity atom to every 100 million silicon atoms.

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Phosphorus has five valence electrons. If 100 million atoms of silicon are doped with an atom of phosphorus, N-type semiconductors result. The N-type material, together with a P-type material, becomes a building block for the simplest semiconductor, known as a diode. To build a diode, a junction is made between an N-type and a P-type semiconductor. On the sides opposite the junction, metal leads are joined to the free end of the semiconductors.

Current flows freely one way in a diode, but almost no current flows in the other direction, which makes the diode a standard device for rectification, or the process of converting alternating current (AC) to direct (DC). A diode is also used for envelope detection where the peak levels of a radio frequency (RF) signal are extracted using a diode detector circuit. This concept suggests the process of audio extraction in amplitude modulation (AM). A diode in conjunction with a resistor-capacitor (RC) circuit of the right time constant generates audio from an AM RF envelope.

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