Investigations on HVPE of non-and semipolar GaN

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As a part of the research group proposal "Polarization field control in nitride light emitters", the current project aims to investigate the epitaxial growth of high quality thick non- and semipolar GaN layers which then can be used as substrates for a subsequent heterostructure deposition. To this end, we will combine the high flexibility of metalorganic vapor phase epitaxy (MOVPE) for the optimization and defect reduction in such layers with the high growth rate of hydride vapor phase epitaxy (HVPE) for the growth of several 100μm thick layers. In the first phase of the project, we have developed a method which allows to achieve semipolar planar surfaces by making use of the c-plane growth direction. This is done by etching grooves with c-plane like side walls into sapphire wafers of specific orientations from which the subsequent epitaxial growth starts. In the second phase, we will optimize this method in particular for the (10_11) plane of GaN grown on (11_23) (n-plane) sapphire wafers to realize large area semipolar planes of GaN with low defect density. Additionally, we will investigate whether this procedure is also applicable to other semipolar surfaces like, e.g. the (20_21) surface. Subsequently, these layers will be overgrown by HVPE to achieve several 100μm thick layers, which eventually can be separated from the sapphire substrates to get free-standing semipolar GaN wafers. By using marker layers, a profound understanding of the growth process can be obtained. Besides varying slightly the substrate misorientation for an improved coalescence of the stripes, we will also study approaches to grow such layers directly by HVPE. The close collaboration with the partners of our research group will help to understand the microstructure of such layers and eventually reduce the crystalline defects typically involved in such non-c-plane growth procedures.