So Who Needs Lattice Matched Heterojunctions Anyway?

Until about five years ago, nearly all optoelectronic and high speed devices with heterojunction structures were made with materials which were lattice-matched, i.e. the unstrained lattice constant of the materials is approximately equal. A large portion of these devices were made from either the GaAs/GaAlAs or InP/InGaAsP system. Early attempts to form devices such as lasers and superlattices using mismatched systems, e.g. GaAs/GaAsP, were disappointing (l), presumably due to the large density of defects at optoelectronically active interfaces needed to accommodate the misfit. This negative result lead to "conventional wisdom'' that active heterojunctions needed to be lattice-matched. Thus, for over a decade, research on such devices as lasers, HEMTs, LEDs, HBTs, and solar cells was restricted to mainly lattice-matched systems. '