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Materials World Network: Growth of nonpolar and semipolar GaN on Si and sapphire substrates and investigation of optical processes for high efficiency

Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Experimental Condensed Matter Physics
Term from 2012 to 2016
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 222080600
 
Final Report Year 2016

Final Report Abstract

As part of the materials world network project “Growth of nonpolar and semipolar GaN on Si and sapphire substrates and investigation of optical processes for high efficiency” experienced an excellent environment formed by the theory support from France and the sample providers from the US. Based on the strong collaboration by direct communication via monthly video conferences and meetings, the project delivered a number of fundamental scientific findings as well as technological improvements. By performing cathodoluminescence, in particular inside a scanning transmission electron microscope with nanoscale resolution, we obtained direct insight into the mechanisms responsible for the formation, evolution, and propagation as well as the termination of extended defects which represent the inherent issue of non- and semi-polar GaN. In detail, we identified the growth domains in three dimensionally grown semipolar GaN on pre-structured substrates to consist of an - due to bending of dislocations - almost defect-free region of excellent material and a highly defect-containing region where the crystal grows locally into the unfavorable [000-1] direction. An optimized coalescence process allowed the overgrowth of the defect reduced part of the GaN over the heavily defect containing part to reduce the impact of the extended defects on the active optoelectronic layers on top. Hence, we could contribute significant developments towards large, planar, and defect reduced semipolar GaN templates. An additional fundamental scientific finding was that an in-situ silicon nitride (SiNx) nano-mask allows the termination of extended defects like basal stacking faults directly within the epitaxy process without growth interruption making external masking procedures obsolete. One main contradictory discussion in the nitride community is focused on the semipolar planes of GaN where (besides the reduced polarization fields) the fundamental different surface adatom kinetics play a significant role regarding the indium incorporation in these planes with respect to the conventional fully polar c-plane orientation. We were able to contribute to this dispute by proofing a significantly larger indium incorporation for InGaN active regions grown on the semipolar (11-22) plane compared to the fully polar (0001) c-plane of GaN. Additionally, we contributed to the development of a photoluminescence-based (PL) method to determine the diffusion length of minority carriers in p-doped as well as n-doped GaN layers. The idea involves an InGaN QW as optically active marker layer to detect the diffusion of the carriers that were generated by absorption of incident PL at the surface. Based on different etched thicknesses of the GaN layer, the dependency of the intensity of the marker layer works as a measure for the diffusion length. Finally, all researchers and especially PhD students of the materials world network project enjoyed a stimulating environment based on networking, strong scientific and personnel exchange. Even more important for the students involved in the project were the frequent student exchanges as well as the advanced training with an individual educational component with scientific supervision and mentoring.

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