Superlattice

The term superlattice (engl. Super lattice ) means a man-made solid state , consisting of a succession of thin layers, which are periodically repeated. Usually there are two alternating layers that differ in the size of the band gap and the layer thickness. The electrons (or holes) are then in a periodically modulated conduction band (valence band). The dispersion in the direction of the superlattice axis results in principle exactly as in the crystal. Since the period is larger than the lattice constant , the Brillouin zone is always smaller than in the case of the crystalline band structure . Because, in contrast to naturally occurring solids, the parameters of the superlattice can be used to determine the energy spectrum of the charge carriers, one speaks of an artificial band structure and, in particular, of mini-bands .

The production of the heterostructures can take place by means of molecular beam epitaxy , CVD or MOVPE .

The periodic disturbances of the lattice structure affect the charge carriers of the original materials and change their properties. For example, the mobility of the charge carriers can be significantly increased (application in high-frequency technology, microwave diodes ) or the optical properties can be adjusted ( semiconductor laser ).

The exactness of the layer sequences is critical for the quality of the superlattice. The layer thicknesses are sometimes on the order of a few atomic layers. Whereby deviations from an atomic position can be detected via changed properties of the electrons.

Quality analyzes are possible with various measuring methods.

Luminescence examinations provide a rather macroscopic view of the overall properties of the crystal . Tunnel microscopy provides an atomic view . Examinations using magnetic resonance methods are in between in terms of measurement accuracy.