Simultaneous growth of various InGaN/GaN core-shell microstructures for color tunable device applications

An approach to simultaneously grow independent core-shell structures emitting at different wavelengths by selective area epitaxy is presented. By using seeds of different sizes, the monolithic integration of various GaN crystals including elongated nano-rods (NRs), micro-platelets (MPs), and a range of pyramid-like structures are demonstrated. Dominant non-polar sidewalls cover more than 75% of the surface area of the NRs, while the polar top facet are about 80% of the total surface of the MPs. InGaN/GaN quantum wells (QWs) deposited on these structures exhibit independent and well-separated emissions in the green-blue and orange-red ranges, respectively. The pyramid-like structures at intermediate seed sizes are more complex with semi-polar facets nearly totaling 60% of the total surface area, resulting in yellow luminescence strongly broadened by the nearby facets contributions. These results suggest the total surface area of each facets and the resulting optical properties of the crystals can be tailored by adjusting the size of the seeds. However, further improvements are required to locally enhance the vertical, pyramidal, and lateral growth of the GaN cores and increase the spectral purity of the different QWs. The approach presented is of interest to design multi-wavelength devices which requires independent subpixels of high color purity. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)