Molecular beam epitaxy (MBE)

Molecular Beam Epitaxy diagram

MBE is an evaporation technique taking place under ultra‑high vacuum (UHV < 10-10 mbar) conditions. Inside the vacuum system, epitaxial films crystallise through the interaction between thermally active atomic or molecular beams of the constituent elements and a substrate which is maintained at an elevated temperature. Molecular beam epitaxy has several key characteristics which makes it an industry and research standard growth system:

  1. It is a very versatile technique, allowing a wide variety of semiconductor alloys to be grown, under non-equlilbrium conditions, through the combined evaporation of its constituent elemental sources.
  2. Abrupt doping profiles such as δ-doping commonly found in high-speed semiconductors can be synthesised.
  3. Slow growth rates (typically 1 monolayer/s) provide for great control over the epitaxial layer thickness.
  4. Excellent thickness uniformity (±1% variation in doping and ±0.5% variation in thickness.
  5. Minimal foreign contamination as a result of the UHV conditions, yielding high purity crystals.
  6. Real-time, in situ characterisation during growth.
  7. High-quality, multi-wafer growth for high volume production.

The other advantage MBE has over other competing systems, namely MOCVD, is that MBE is less hazardous as it does not employ any dangerous chemical pre-cursors. 

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