Sekwencyjny proces epitaksji warstw atomowych w warunkach przepływu gazu i wysokiej próżni

Essential features of atomic layer epitaxy (ALE) are reviewed with particular attention being paid to the growth of monocrystalline films under the gas flow conditions. The sequential supply of chemical reactants (so-called precursors) - separated by purging phases - causes the basic effect: an introduced precursor finds a reaction partner exclusively in the adsorption layer. Consequently, the process can be considered as deposition (or epitaxy if monocrystalline film is obtained) from adsorption layers. The kind of surrounding medium plays a secondary role by delivering the precursors and removing the reaction by-products. Owing to the surface tension in the adsorbed layers, the produced solid films are smoother than those obtained by alternative procedures. ALE may be achieved in the gas flow system (ALE-GF), as well as a mode of molecular beam epitaxy (ALE-MBE). The differences for applications between the two result from the molecular and continuum flows — shadowing is easier in the high vacuum, while the gas environment gives better possibilities to produce continuous films of uniform thickness in grooves or on irregularly shaped substrates. The basic phenomena of ALE-GF are related to those appearing in the heterogeneous catalysis, but the considered deposition creates a solid phase product, and sequential control over the process is applied. Low costs and easy employment of different reactions -synthesis, single or double exchange - increase the attractiveness of sequential deposition in gas flow. Until now largescale use of the sequential procedure has been developed in production of microcrystalline films (also called in this case atomic layer deposition ALD) for colour displays, chemical catalysts as well as insulating and anticorrosion coatings. The expansion of the sequential processing ALE in the gas flow version seems to be still limited to a few geographic regions: Finland, the motherland of the method, remains the leader in the deposition of microcrystalline films - also in cooperation with a few US and European companies and research centres. The USA maintain the leadership in monocrystalline til—V films, although a few East-Asian countries (Japan, especially) joined quickly and, in addition, initiated the growth of monocrystalline II-VI semiconductor films. Research in the latter direction is also progressing in Poland, where monocrystalline films of zinc and cadmium sulphides and selenides have been obtained, and also production of microcrystalline ZnO-buffers for GaN deposition is being developed.