Basic Description of MBE

In MBE, the constituent elements of a semiconductor in the form of ‘molecular beams’ are deposited onto a heated crystalline substrate to form thin epitaxial layers. The ‘molecular beams’ are typically from thermally evaporated elemental sources, but other sources include metal-organic group III precursors (MOMBE), gaseous group V hydride or organic precursors (gas-source MBE), or some combination (chemical beam epitaxy or CBE). To obtain high-purity layers, it is critical that the material sources be extremely pure and that the entire process be done in an ultra-high vacuum environment. Another important feature is that growth rates are typically on the order of a few Å/s and the beams can be shuttered in a fraction of a second, allowing for nearly atomically abrupt transitions from one material to another.