Mechanisms of Optical Transitions in AlGaN Alloys and GaN/Al GaN Quantum Wells

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This project addresses optical transitions and carrier dynamics in GaN/AlGaN quantum well (QW) structures; mechanisms of optical transitions in AlGaN epilayers with high AlN mole fractions; and effects of reduced volume and optical confinement on the optical and optoelectronic properties of GaN microstructures including micro-disks, prisms, and pyramids. Picosecond time-resolved photoluminescence will be used to study the mechanisms of optical transitions in a variety of III-nitride samples and structures, and, in conjunction with additional characterization techniques, to provide information on sample crystalline quality, purity, alloy composition, and quantum well interface properties. Emphasis will be placed on AlGaN with high AlN mole fractions. Additionally, since many III-nitride based applications take advantage of heterojunctions and multiple quantum wells (MQW), AlGaN/GaN and AlxGa(1-x)N/AlyGa(1-y)N(y x) heterojunction and MQW structures and the tunability of the bandgap in the alloys from GaN (Eg=3.4 eV ) to A1N (Eg=6.2 eV) will be explored for achieving greater understanding of fundamental deep ultraviolet (UV) optoelectronic phenomena associated with these materials. Materials synthesized by both MBE and MOCVD will be studied. Research efforts will address properties which affect selective and lateral growth including crystallographic orientation as well as buffer layers. Quantum well thickness, doping concentration in the barrier layers, alloy composition in the AlGaN layers, and post-growth processing conditions will be studied to assess n- and p- type doping in AlGaN alloys, defect energy levels, self-compensation, and the formation of deep level impurities in AlGaN. Structural characterization includes TEM, AFM, SEM and X-ray analyses; SIMS, optical spectroscopy, and Hall effect measurements will be used to assess compositional and electrical properties.%%%