Fundamental Properties of GaAsN and InGaAsN - Toward Optoelectronic Applications

Texas Tech University, Lubbock TX

Investigators

Abstract

It is proposed to grow and characterize ternary alloys of conventional III-V compounds (e.g. GaAs, InAs) with III-N compounds (e.g. GaN, InN) on GaAs substrates. These alloys are expected to be cubic with the zincblende structure and to possess a direct bandgap. However, the large lattice mismatch between GaAs and GaN and the difference in atomic orbital energies between As and N result in a very unusual compositional dependence of the bandgap. The optical bowing coefficients in GaAs1-xNx are at least an order of magnitude greater than those encountered in common III-V alloys. Its bandgap decreases rapidly with increasing N fraction. This offers a possibility of preparing novel optoelectronic devices, on GaAs substrates, operating in the 1.3 - 1.55 mm range. The materials needed for this study will be grown by Metalorganic Molecular Beam Epitaxy (MOMBE). The effect of nitrogen incorporation on physical microstructure and optical bandgap of epitaxial layers will be determined by a variety of experimental techniques. Raman scattering will be used to investigate microstructural effects such as nitrogen incorporation, spontaneous ordering, and phase separation. Raman results will be modeled using bond polarizability, a two-component molecular model, finite size, and strain effects. Near band edge optical properties will be studied extensively by cw and time-resolved photoluminescence. These will focus on how nitrogen incorporation modifies carrier recombination. Ellipsometry and reflectance methods will be used to gain information of the above-bandgap optical properties. Phenomenological deformation potentials model will be used to account for strain effects in quantum wells and superlattices of InGaAsN/GaAs. Finally, quantum well structures based on InGaAsN/GaAs will be used as active layers to make vertical cavity lasers operating in the wavelength range of 1.3-1.55 mm.