Active region methods

Epitaxial crystal growth methods such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have advanced to the point that active regions of essentially arbitrary thicknesses can be prepared (see Thin films, film deposition techniques). Most semiconductors used for lasers are cubic crystals where the lattice constant, the dimension of the cube, is equal to two atomic plane distances. When the thickness of this layer is reduced to dimensions on the order of 0.01 )J.m, between 20 and 30 atomic plane distances, quantum mechanics is needed for an accurate description of the confined carrier energies (11). Such layers are called quantum wells and the lasers containing such layers in their active regions are known as quantum well lasers (12). 

The important feature in the SL method is that there is always a buffer of dormant SL region separating any two dynamically active regions, which eliminates the difficulty associated with synchronizing events and resolving conflicts at the boundaries between processors. For a finite cycle time, the SL method is not exact, but if the cycle time is comparable to or shorter than a typical reaction time, it is extremely accurate. A detailed discussion and demonstration of the requirements for accuracy in the case of KMC can be found in ref. 35. 

One of the very active regions of research in recent years has involved attempts to extend experimental methods to provide additional spectral information for more definitive electronic state assignments. 

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