Epitaxy is a process used to deposit a layer of crystalline material on top of a substrate made of crystal. Silicon is often used for semiconductors and can be modified through doping. An epitaxial layer can be lightly doped and placed on top of a more heavily doped substrate to create a faster chip. Epitaxial reactors are used to deposit these layers, and the process is used in various applications, including electronics and biology. Epitaxial graphene is being developed as a replacement for silicon in microelectronic devices.
Semiconductors and computer circuits are often made using crystalline materials. A process called epitaxy can be used to deposit a microscopic layer of crystalline material on top of a substrate that is also made of crystal. The deposition process is called epitaxial growth, because crystals typically grow in place once they are attached to the substrate. Silicon is often used for semiconductors, in a process called homoepitaxy, which means that 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 of choice 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 top of a substrate that is more heavily doped. The finished device is often able to operate at higher speeds on the same current as a slower chip.
Epitaxial silicon can also be used to manage the doping process and adjust material concentrations. Growing one layer on top of another generally creates a device with two electrically different components. In some cases, a layer may be oxygen-free or may be designed to be completely filtered out of carbon molecules.
An epitaxial reactor is often used to deposit these layers. The 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 in a quartz reaction chamber to physically support the silicon wafers and distribute heat evenly within the computing system.
Devices that often incorporate a crystal layer include solar cells and alternating current (AC) to direct current (DC) converters. The process is often used in electronics, but has also been integrated into biological, scientific, engineering and chemical applications. Another material that the concept can be used with is epitaxial graphene. A layer of carbon atoms is typically arranged in a two-dimensional, graphite-like honeycomb shape on large sheets that are electrically conductive.
Epitaxial graphene was developed on the basis of carbon nanotube processing in the early 21st century. Researchers often envision it as a future replacement for silicon in microelectronic devices and miniaturized circuits. The processes for growing this substance are generally similar to those for manufacturing silicon components.
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