Browsing by Author "Kujala, Sami, D.Sc."

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    Semiconductor quantum structures for applications in the near infrared and blue regions
    (Aalto University, 2016) Mattila, Päivi; Kujala, Sami, D.Sc.; Huhtio, Teppo, Docent; Mikro- ja nanotekniikan laitos; Department of Micro and Nanosciences; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Sopanen, Markku, Prof., Aalto University, Department of Micro- and Nanosciences, Finland
    In this work, semiconductor quantum structures are studied to show enhanced performance in the near-infrared and blue wavelength regions. The techniques presented in this thesis include AlN passivation of GaAs surfaces and GaAs-based quantum dot structures in the near-infrared region. In the blue wavelength region, one-dimensional metal gratings are fabricated on GaN structures. All of these techniques have potential applications in optoelectronic components including nanowire-based detectors, metal-insulator-semiconductor structures, and light-emitting diodes.  The GaAs-based structures are fabricated by metalorganic vapor phase epitaxy, and the AlN layers are deposited ex situ by plasma-enhanced atomic layer deposition. The passivation effect is verified by photoluminescence, time-resolved photoluminescence, photoreflectance, and capacitance-voltage measurements. The comparison of pure plasma and AlN passivation shows that plasma has a role in the process. The effect cannot, however, be entirely explained by plasma, and hydrogen is suggested to affect the passivation.  When the AlN layer thickness is further increased, the delicate strain-induced quantum dots are covered without reducing the integrated photoluminescence intensity. In addition, the energy redshift of the quantum dot states is not affected by the covering with AlN. Thus, AlN can be used to cover these delicate structures.  GaAsN islands are fabricated on InP by annealing tensile-strained GaAsN layers. The nitrogen in the layer reduces the band gap of GaAs. Therefore, the photoluminescence intensity maximum is observed to shift towards the longer wavelengths of optical telecommunications.  In the blue wavelength region, the GaN structures are characterized by photoluminescence, angle-resolved photoluminescence and reflectometry measurements. When a polyvinyl alcohol layer is fabricated on top of the InGaN/GaN sample, the enhancement of emission is observed in both TM and TE polarizations. The photoluminescence intensity is shown to increase by a factor of up to 2.8.