Electrically Injected Ultraviolet AlGaN Photonic Nanocrystal Surface Emitting Lasers

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This project is related to the demonstration of surface emitting semiconductor lasers operating in the mid-ultraviolet (UV) spectrum, which will enable many revolutionary applications, ranging from replacing bulky and toxic excimer lasers in the production of integrated circuits to ultra-high-density optical storage to high-resolution spectral analysis and biomedical diagnosis. To date, there have been no demonstration of surface emitting laser diodes operating in the mid and deep UV spectra, which has been limited by the presence of extensive defects and dislocations of conventional aluminum gallium nitride (AlGaN) materials, poor current conduction, and low reflectivity of AlGaN-based distributed Bragg reflectors (DBRs). Consequently, the current mid and deep UV light sources are based on mercury and xenon lamps, which are power hungry, bulky, and expensive and often contain toxic substances. In this project, by utilizing aluminum gallium nitride nanostructures, the researchers will address these fundamental challenges and will design and develop a new generation of surface emitting laser diodes that can operate efficiently in the UV spectrum. Success of this project will open a new paradigm for achieving efficient solid-state UV light sources, which may enable the only likely alternative technology to replace conventional excimer lasers and mercury lamps for water purification and disinfection. This project provides the opportunity to educate students in a broad range of topics, ranging from nanomaterials, photonics, nanotechnology, and optoelectronics. The highly interdisciplinary nature of the proposed research also allows the investigator to provide research and training opportunities to involve undergraduate, underrepresented minorities, and K-12 through various planned activities. In this project, the investigator proposes to develop all-semiconductor based, electrically injected, low threshold surface emitting laser diodes operating in the UV-B band (280-315 nm). Surface emitting lasing will be achieved by exploiting the two-dimensional resonance modes of dislocation-free aluminum gallium nitride (AlGaN) photonic nanocrystals, instead of using conventional resistive and dislocated AlGaN distributed Bragg reflectors (DBRs). Moreover, efficient p-type conduction, that was not previously possible in wide bandgap aluminum nitride (AlN) and Al-rich AlGaN, will be achieved by exploiting the formation of a magnesium (Mg) acceptor impurity band in defect-free AlGaN nanocrystals. (Al)GaN dot-in-nanocrystal heterostructures will be grown and characterized, which will overcome the challenges associated with nonradiative surface recombination, as well as the large transparency carrier density of wide bandgap semiconductors, thereby enabling low threshold UV lasers that were not previously possible. A detailed understanding of the laser performance, including threshold, wall-plug efficiency, near and far-field profile, stability and reliability will be performed. Success of this project will open a new paradigm for developing low threshold surface emitting laser diodes operating in the UV spectrum, wherein the device performance is no longer limited by the lack of high quality DBRs, large lattice mismatch, and substrate availability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.