Wide band-gap II-VI compounds - can efficient doping be achieved?

Direct band-gap Il-VI semiconductors have a potential for a variety of light-emitting devices spanning the entire range of the visible spectrum, should the persevering difficulties in achieving efficient doping be solved. In this paper a number of possible doping-limiting mechanisms and various approaches to avoid or overcome them are summarized and analyzed, including author's personal contributions to these efforts. The main mechanisms limiting efficient doping in equilibrium conditions have been identified as: compensation by native defects and/or pairs, lattice relaxation around doping atom resulting in formation of compensating deep localized levels, amphoteric behavior of some prospective dopants, and insufficient solubility of the others. The greatly extended theoretical and practical work in understanding relevant mechanisms during the last several years confirmed the seriousness of the doping problems, but at the same time showed the way toward their solution(s). New approaches include: low temperature crystal growth (particularly with MBE and other low-temperature growth/doping techniques), doping by ion implantation, co-doping with more than one dopants, etc. The most promising way to solve the doping problems in Il-VI compounds are nonequilibrium processes, where excellent results have been obtained, opening the ways for much wider applications of these materials in the near future. (C) 1998 Elsevier Science Ltd. All rights reserved.