Long-wavelength lasers emitting at ?= 1.33 or 1.55 m are one of the most important and widely used optoelectronic devices for optical fiber communication systems in the present modern information technology era. For optical-fiber communications, the lnGaAsP quaternary III-V semiconductor material system, which is lattice-matched to InP, covers the wavelength range corresponding to low dispersion or low attenuation in optical fibers. Therefore, lasers for optical communication application with low dispersion or low attenuation have been developed and commercialized using an InGaAsP active layer grown on InP substrates. However, InP-based lasers have generally inferior characteristic performance compared to GaAs-based lasers. Especially for vertical-cavity surface-emitting lasers (VCSELs), lnP -based lasers have been problematic due to the lack of good lattice-matched distributed Bragg reflector (DBR) material combinations, which should have high refractive index contrast, low electrical resistance, and low thermal resistance. Compared to lnP-based VCSELs, GaAs-based VCSELs with AlAs/GaAs DBR mirrors have better characteristics. However, the system performance characteristics, such as the transmission capacity, are limited by the bandwidth of compatible multimode fibers, since they have a short-wavelength spectral range (?~O.85 m). To obtain high-performance long-wavelength lasers, the ideal practical combination should be that of an ~active layer" emitting in the long-wavelength range compatible with the well-established GaAs-based laser technologies. The GaAs system offers several important advantages over the alternate InP-based system, including larger area wafer processing, better thermal properties higher doping concentrations, an oxidation-compatible material system, and high-performance DBR materials. Several possible approaches have been proposed and investigated. One of the most promising is explored here. The study of InAlGaAsSb epitaxial growth using MOCVD is a research topic that is of increasing interest throughout the world. The realization of high-quality epitaxial layers and heterojunctions are important elements in the development of advanced semiconductor devices, in particular, VCSELS. The research proposed here will result in the practical realization of X=1.33pm VCSELs as well as for the study of the fundamental properties of Sb-based heterojunctions and in the study of Ill-Sb quantum dots. The work of the primary topic of the study of Sb growth and fundamental properties couples directly to that of a second research topic on devices, specifically, VCSELs-an area that we are already exploring with collaborators at Agilent Technologies. This research will provide new fundamental insight into the physics of two-dimensionally confined systems in Ill-Sb materials. These topics have a strong potential for broad impact in optoelectronics and also in electronics, e.g.. high-speed electronics could be developed.