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978-3-8439-3643-9, Reihe Physikalische Chemie
Anna Katharina Haab
Indium Gallium Nitride Nanostructures for Optoelectronic Applications
164 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2018), Softcover, A5
The present thesis addresses the fabrication and characterisation of nanowires consisting of the indium gallium nitride (InGaN) material system. The group III-nitrides have become established in application for optoelectronic devices in the last years and are of great interest for research and industry. Particularly the use of gallium nitride (GaN) - InGaN heterostructure layers as the basis for light emitting diodes (LEDs) has to be pointed out. They are not only utilized as energy-efficient light sources but further as blue lasers in Blu-ray players and as background lighting in displays. Creating nanostructures, especially nanowires, out of this material system is promising to boost device efficiencies.
In this work three different approaches to fabricate nanowires were pursued. One is the creation of GaN nanowires by reactive ion etching (RIE). Epitaxially grown GaN layers were introduced into the etching chamber without lithographic structuring. The following characterisation of the nanowires, in direct comparison with their layer counterpart, revealed the nanowire formation mechanism during this process and enabled to gain control of the nanowire morphology. Moreover, they show excellent optical properties, which were investigated by photoluminescence spectroscopy, as well as transmission and reflection spectroscopy.
In a further step the GaN nanowires formed by plasma etching were used as growth substrate for an InGaN shell. The InGaN shell was grown by metal-organic vapour phase epitaxy (MOVPE). In these experiments different compositions of the ternary alloy were formed. A comparatively high In content could be reached compared to literature values of planar InGaN layers.
Furthermore, InN nanowires were grown by MOVPE on Si wafers. In contrast to common approaches for group III-nitride growth on Si no aluminium nitride (AlN) buffer layer was used. It was also refrained to use foreign metals like Au, to catalyse the nanowire growth via the so-called vapour liquid solid (VLS) method. Instead, the InN growth was promoted by metallic In droplets on the Si wafer. The resulting nanowires exhibit a V-shaped morphology and are split in two mirror-symmetric crystals by a twin plane. Based on these results a further development of the nanowires regarding their morphology, optoelectronic properties and integration in devices can be promoted.