There is an increasing technological need for a wider array of semiconducting materials that will allow greater control over the physical and electronic structure within multilayer heterostructures. This need has led to an expansion in the range of semiconducting alloys explored and used in new applications. These alloy semiconductors are often complicated by a limited range of miscibility. The current research has focused on the properties, stability, and detailed chemistry required to realize these materials. The use of synthetic conditions that permit the growth of these alloys to be dominated by kinetic rather than mass-transport considerations has allowed many of these nominally unstable materials to be grown and used in device structures. These materials have found important applications within optical communications as emitters and detectors and in solid-state lighting.