Giving a new life to an old material ZnO

摘要

Oxide thin film epitaxy has gained tremendous progress since the intensive research in the field of high Tc superconductors triggered at the discovery by Bednortz and Muller. This can be well compared with the progress and success of molecular beam epitaxy (MBE) of GaAs after the prediction of superlattices by Esaki. As a result of the development of MBE, we can now enjoy the fruits in computers, communications and internets, etc. The question here is what can we expect from the progress of oxide epitaxy in the next a few decades. I shall not discuss on the high T_c devices but on more improtant progress. Atomic scale control of oxide epitaxy is now possible in part of the heteroetpitaxial systems. Especially, we have focused our efforts on the dimension control of oxide epitaxy. Two-dimensional epitaxy in layer-by-layer mode provides tunnel junctions and superlattices, whereas that in step-flow mode enables us to produce very high crystallinity thin films and nano-wire structures. Nanocrystalline dot structures of ZnO deposited in well-controlled island growth mode have explored a new field of oxide semiconductor technology.