A molecular beam epitaxy system is a device that is capable of depositing single crystals. Layers with an atomic thickness are placed down onto substrates. To do this, a molecular beam must be created in order to influence the substrate. This beam refers to the evaporated atoms during the process, which will not interact with each other until they are deposited on the wafer. MBE systems can also be used for the deposition of some organic semiconductors. In this case, molecules are deposited onto the wafer rather than atoms.
Molecular beam epitaxy systems require a high vacuum to work. This is because it must have a very low gas pressure from the outside world. MBE also has a slow deposition rate, so this vacuum allows the system to obtain the necessary impurity levels. Ultra pure elements are heated in effusion cells, getting hotter and hotter until they begin to sublimate. These elements will react with each other once they have re-condensed on the wafer.
To make sure all goes well during the process, crystal growth must be measured using a Reflection High Energy Electron Diffraction (RHEED) system. This technique will brand the surface of the crystal during molecular beam epitaxy. The crystal thickness is carefully controlled using computers to open and close the shutters in front of each furnace. This method of control assures that multiple different layers can be easily crafted into a variety of intricate layers, which are a crucial part of many semiconductor devices.
Cyropumps are also observed in molecular beam epitaxy in relation to cooling substrates once they are heated. The temperatures act as a sink for the impurities, meaning the vacuum needs to be of a greater magnitude of cryogenics are to be used. Wafers, the areas where the crystals are grown, can also be mounted on a rotating platter, which is then heated to several hundred degrees Celsius. This type of molecular beam epitaxy system eliminates the need for cryopumps, which are not integral to MBE.
Molecular beam epitaxy is a very important process to the semiconductor industry, and the systems which control this are a central part of the process. Used to grow and develop high purity crystals with very precise dimensions, molecular beam epitaxy systems take excess molecules or atoms and allow them to condense on a substrate, where they begin to form ultra-thin layers of crystal. This technique is optimal in the design of semiconductor lasers, thin films, solar cells and many other types of devices for the semiconductor. With its excellent accuracy and precision, molecular beam epitaxy is an amazing yet simple way to engineer crystals.