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Title: Photoluminescence blueshift mechanisms in molecular beam epitaxy grown dilute nitride hetrostructures
Keywords: GaInNAs, MBE, Indium segregation, Interdiffusion, Short-range-order, Genetic algorithm
Issue Date: 21-Aug-2009
Citation: VIVEK DIXIT (2009-08-21). Photoluminescence blueshift mechanisms in molecular beam epitaxy grown dilute nitride hetrostructures. ScholarBank@NUS Repository.
Abstract: Low cost access to optical communication networks is the backbone of modern day optical communication systems for high speed internet data transmission. Cost effective light sources in the low loss window, 1.2-1.6 µm, are required for large scale deployment of high performance communication network systems. Dilute nitrides have been identified as promising material at 1.3 and 1.55 µm emission wavelengths for commercial applications in telecommunications. They have attracted considerable experimental and theoretical interest due to their unusual physical properties and great potential in optoelectronic devices for telecommunication. They exhibit a large reduction in bandgap energy due to the addition of small amounts of Nitrogen in GaInAs to form GaInNAs. GaInNAs offers several advantages, e.g. type-I band lineup, effective electron confinement, higher electron effective mass and lattice matched (pseudomorphic) growth on GaAs substrate allowing one to take advantage of mature DBR technology and easy monolithic integration with GaAs electronics to provide low-cost, high speed electrical drivers for lasers in high speed networks. In this work, GaInNAs/GaAs quantum structures are investigated for their structural and optical properties. GaInNAs/GaAs quantum wells (QWs) are grown using plasma assisted molecular beam epitaxy. Theoretical modeling is performed to estimate the effects of Indium segregation, short range order and interdiffusion on photoluminescence blueshift in GaInNAs/GaAs QWs. A kinetic model is presented to explain the observed Indium segregation trend in GaInNAs due to the incorporation of Nitrogen. Theoretical results are presented for the effect of composition disorder, resulting from Indium segregation and non-uniform Nitrogen composition on band structure and TE and TM mode optical gain of the GaInNAs/GaAs QWs. The presence of composition disorder of Indium and Nitrogen in the quantum wells can cause blueshift in transition energy, but Indium segregation plays the major role. The transition energy blueshift due to Indium segregation is significant only for segregation efficiencies greater than 0.6. Composition disorder also tends to increase the threshold current density for GaInNAs/GaAs QW lasers. Rapid thermal annealing is performed to improve the optical and crystalline qualities of as-grown GaInNAs material by overcoming crystal defects arising from plasma damage or interstitial incorporation of Nitrogen. The undesirable blueshift resulting from annealing is studied and explained in terms of two responsible mechanisms: rearrangement of local Nitrogen bond configurations N-GamIn4-m (0 = m =4), also known as short-range order (SRO), and Gallium/Indium atom interdiffusion across the QW/barrier interface. The individual contributions from both mechanisms are calculated using an original approach based on a genetic algorithm. The activation energies for SRO and interdiffusion are estimated to be 2.3 eV and 3.25 eV respectively, indicating the important role played by SRO at low temperature and at the beginning of annealing process.
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