Molecular beam epitaxy (short MBE)

Molecular beam epitaxy (MBE) is a technology, with atomical resolution, which allows the growth of materials on single crystals in ultra-high vacuum (UHV). Good UHV (~1e-11 hPha) conditions and RGA analysis are essential for good epitaxial quality. Nowadays, MBE is widely used for the production of semiconductor devices. It is also one of the most important techniques for Nano- and Quantum technologies.

How it works
In solid source MBE, ultra-pure elements such as gallium and arsenic are thermally evaporated in vacuum (from 10-8 hPa to 2x10-5 hPa typical). The atomic fluxes from the cells reach the wafer where the epitaxial growth can happen. In the example of gallium and arsenic, single-crystal gallium arsenide is formed. The atoms impinging on the surface adsorb, migrate and incorporate into crystalline lattice of the wafer. They also can desorb if the substrate temperature is too high. Controlling the temperature of the source will control the rate of material impinging on the substrate. The substrate temperature affects the migration length and desorption rate. The term "beam" means that evaporated atoms do not interact with each other or residual gases until they reach the wafer, due to the long mean free paths of the atoms at low pressure. Therefore, simple mechanical shutters can be used to abort the flux.

Why Vacuum and Product Portfolio
Molecular-beam epitaxy takes place in high vacuum or ultra-high vacuum (10-8 – 10-12 hPa). The typical MBE deposition rate is 1,000 nm in hour. That allows the films to grow epitaxially. These deposition rates require proportionally better vacuum to achieve the same impurity levels as other deposition techniques. The absence of carrier gases, as well as the ultrahigh vacuum environment, results in the highest achievable purity of the grown films. Pfeiffer Vacuum provides different dry rough pumps and turbopumps with high compressions ratios. For MBE applications, Pfeiffer Vacuum also can provide vacuum gauges to control the pressure in the system and mass spectrometers to perform the residual gas analysis (RGA).

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