Fundamental Properties of GaAsN and InGaAsN - Toward Optoelectronic Applications

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It is proposed to grow and characterize ternary alloys of conventional III-Vcompounds (e.g. GaAs, InAs) with III-N compounds (e.g. GaN, InN) on GaAssubstrates. These alloys are expected to be cubic with the zincblende structure and topossess a direct bandgap. However, the large lattice mismatch between GaAs and GaNand the difference in atomic orbital energies between As and N result in a very unusualcompositional dependence of the bandgap. The optical bowing coefficients in GaAs1-xNxare at least an order of magnitude greater than those encountered in common III-Valloys. Its bandgap decreases rapidly with increasing N fraction. This offers a possibilityof preparing novel optoelectronic devices, on GaAs substrates, operating in the 1.3 - 1.55mm range. The materials needed for this study will be grown by Metalorganic MolecularBeam Epitaxy (MOMBE). The effect of nitrogen incorporation on physicalmicrostructure and optical bandgap of epitaxial layers will be determined by a variety ofexperimental techniques. Raman scattering will be used to investigate microstructuraleffects such as nitrogen incorporation, spontaneous ordering, and phase separation.Raman results will be modeled using bond polarizability, a two-component molecularmodel, finite size, and strain effects. Near band edge optical properties will be studiedextensively by cw and time-resolved photoluminescence. These will focus on hownitrogen incorporation modifies carrier recombination. Ellipsometry and reflectancemethods will be used to gain information of the above-bandgap optical properties.Phenomenological deformation potentials model will be used to account for strain effectsin quantum wells and superlattices of InGaAsN/GaAs. Finally, quantum well structuresbased on InGaAsN/GaAs will be used as active layers to make vertical cavity lasersoperating in the wavelength range of 1.3-1.55 mm.