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What Is Epitaxial?

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  • Written By: Andrew Kirmayer
  • Edited By: Shereen Skola
  • Last Modified Date: 21 November 2016
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Semiconductors and computer circuits are often manufactured using crystalline materials. A process called epitaxy can be used to deposit a microscopic layer of crystal material on top of a substrate that is also made of crystal. The deposition process is called epitaxial growth, because the crystals typically grow in place once set on the substrate. Silicon is often used for semiconductors, in a process called homoepitaxy, which means the deposited and target materials are the same. The epitaxial layer is most often produced by a manufacturing process called chemical vapor deposition.

Silicon is typically electrically conductive and is usually the material chosen for computer chips. Manufacturers often modify it in a process called doping to change the electrical properties. Additional materials can be added to pure silicon to achieve this. An epitaxial layer can be lightly doped, and be placed on a substrate that is more heavily doped. The finished device is often able to run at faster speeds under the same current as a slower chip.

Epitaxial silicon can also be used to manage the doping process and adjust the concentrations of material. The growth of one layer on top of another generally creates a device with two electrically different components. In some cases, one layer can be oxygen-free, or it can be designed to be completely filtered of carbon molecules.

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Often, an epitaxial reactor is used to deposit these layers. Gases are typically injected into the reactor chamber, which is heated. These gases usually react with silicon carbide. An epitaxial layer is then formed, while the rate of growth can be controlled using a carrier gas. A susceptor can also be placed into a quartz reaction chamber to physically support silicon wafers and evenly distribute the heat within the processing system.

Devices that often incorporate a crystal layer include solar cells, as well as alternating current (AC) to direct current (DC) converters. The process is often used in electronics, but it has also been integrated into biological, scientific, engineering, and chemistry applications. Another material with which the concept can be used is epitaxial graphene. A layer of carbon atoms is typically arranged into a two-dimensional honeycomb shape, similar to graphite, over large sheets that are electrically conductive.

Epitaxial graphene was developed based on the processing of carbon nanotubes at the beginning of the 21st century. Researchers often consider it as a future replacement to silicone in microelectronic devices and miniaturized circuits. The processes for growing this substance are usually similar to those for manufacturing silicon components.

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