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978-3-8439-0562-6, Reihe Physik
InGaN active regions on semipolar pyramidal GaN templates
197 Seiten, Dissertation Universität Stuttgart (2012), Hardcover, A5
Indium gallium nitride (InGaN) is a material which is very interesting for optoelectronic devices because by varying the indium content in the InGaN alloy, the band gap can be varied from 3.51 eV (354 nm, GaN) to 0.69 eV (1796 nm, InN), covering the whole visible spectrum. This is especially needed for lighting applications and portable projectors. The fabrication of such devices, however, poses extraordinary challenges, especially for devices in the green to orange spectral range.
The material quality deteriorates at high indium contents, piezoelectric fields lower the device efficacy on polar planes and native substrates are currently expensive and not widely available, especially for arbitrary growth planes. The approach taken in this work to meet these challenges is to grow the active regions of optoelectronic devices on the semipolar side facets of micropyramids as templates. The semipolar planes lower the impact of the quantum confined stark effect (QCSE) on the active regions. The micropyramids can also be produced in a cost-effective way on c-plane GaN layers grown on conventional heterosubstrates, eliminating the need for native substrates. Additionally, the indium incorporation is different on the pyramid side facets than on planar c-plane layers.
In this work, we will first discuss the production of the semipolar templates. The material quality of the pyramids has a high impact on the active regions and therefore, close attention has to be paid on the growth conditions of the pyramids. Especially the initial growth steps turned out to be critical. Afterwards, the focus is shifted to the growth of the active regions. During active region growth, a coaction of different growth processes leads to a high indium incorporation on the pyramid side facets and to an indium redistribution to the edges and tips, enhancing the luminescence in the green to orange spectral region. Highly spectrally and spatially resolved measurements are employed to investigate the mechanisms involved. The tuning of these processes is also discussed to allow for band gap engineering. The last step taken in this work is the conversion of the pyramids into LED structures. It could be shown that the features formed by the indium incorporation mechanisms observed on the side facets are also present in finished LED structures, making it possible to exploit the characteristics of the pyramids for device fabrication.