This project is related to the demonstration of white-color and full-color surface-emitting lasers, which have the potential to revolutionize next-generation lighting, display, sensing, and communication technologies. To date, there are no efficient semiconductor lasers operating in the deep visible (green and yellow) spectral range, which has been limited by the presence of large densities of defects in gallium nitride based materials. Consequently, the current commercial green lasers generally rely on the use of nonlinear optical conversion. Such devices, however, are bulky, heavy and expensive, and are not suitable for on-chip integration. Moreover, there has been no established manufacturable technology to spatially vary alloy compositions to achieve multi-color emission on the same substrate. As a result, the current solid-state lamps rely on the use of rare earth doped phosphors to down-convert the blue emission of a gallium nitride based light emitting diode (LED) to generate white-light, which limits the flexibility to tune the spectral power distribution and to achieve color-tunable emission. In this project, by using gallium nitride based nanostructures, the applicant will address these fundamental challenges and demonstrate small size, high efficiency multi-color lasers. This project will address the "green gap" in semiconductor light emitters and will enable phosphor-free solid-state lighting, thereby significantly enhancing the efficiency, reducing the manufacturing cost, and improving the light quality. The broader impacts of this research also include the highly interdisciplinary nature of the proposed research and the outreach to undergraduate, underrepresented minorities, and K-12. This project also provides the opportunity to educate the students involved in the research and to involve high school students on the science and technology of nanostructured materials, LED lighting, and photonics.
The applicant proposes to demonstrate white-color and full-color surface-emitting lasers through innovations in epitaxy, quantum-confined nanostructures, nanophotonics, and device engineering. Full-color emission will be achieved on a single chip by varying the nanowire diameters through selective area epitaxy, which was not previously possible for gallium nitride based quantum wells. Moreover, nonradiative surface recombination, one of the primary limiting factors for nanowire devices, will be addressed by using dot-in-nanowire core-shell heterostructures. In this project, surface-emitting lasers will be achieved by exploiting the two-dimensional band-edge resonant effect of a nanowire photonic crystal, instead of using conventional thick and resistive distributed Bragg reflectors. The unique approach will also enable the monolithic integration of red, green and blue emitters on a single chip, thereby leading to full-color and white-color laser diodes that were not previously possible. The device characteristics, including threshold, wall-plug efficiency, near and far-field profile, and modulation characteristics will be investigated.
