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978-3-8439-3487-9, Reihe Ingenieurwissenschaften
MOVPE selective area growth of GaN/InGaN rod and fin core-shell LEDs
190 Seiten, Dissertation Technische Universität Braunschweig (2018), Hardcover, A5
Three-dimensional (3D) architectures of GaN are interesting for several applications as e.g. LEDs, sensors or field-effect transistors. Being grown in a bottom-up technique, these 3D architectures feature a high crystalline quality. Additionally, they have large surfaces and non-polar facets, which can be beneficial for optoelectronic applications. The most controllable, bottom-up technique for the fabrication of these 3D architectures is selective area growth by metalorganic vapour phase epitaxy (MOVPE).
Even though 3D architectures in a rod shape were in the focus of research over the last years, a wall-shaped geometry provides several advantages in comparison to the rod structures. These so-called fin structures suffer less from edge effects, provide enhanced surface areas (e.g. for light emission) and offer the possibility for a fast investigation of their internal properties. It was found that the reproducibility of the epitaxial process was improved for fins in comparison to rods. Moreover, under similar SiH4 flows, the vertical growth rate of fins was higher than of rods. Due to all these benefits, the selective area growth of fins was analysed in detail within this thesis.
Fins with high aspect ratios and large non-polar a-plane sidewalls evolved under the applied continuous mode MOVPE. The impact of the most important epitaxy parameters (growth durations, SiH4 flow, temperature, pressure, V/III ratio, trimethylgallium and ammonia flow) on the geometry, surface roughness and homogeneity of fins was studied in detail. Based on all these findings, the fin growth was considerably improved by the application of the 2-temperature-step-growth process. With the help of this new process, fins with smooth sidewalls and top facets and a very high homogeneity along their length as well as over different mask patterns were achieved. Besides this, a model for the selective area growth of fins was extracted out of marker-layer experiments.
Using the fins as cores, core-shell fin LEDs were developed. A shell consisting of an InGaN QW and a p-doped GaN layer was grown around the fin cores. The impact of several epitaxial parameters during InGaN shell growth (pressure, duration, temperature, trimethylindium and triethylgallium flow) on the distribution of the QW along the sidewalls was investigated. Electroluminescence of a single fin LED revealed QW emission from the non-polar sidewalls in the violet-blue spectral region.