Development of chip-scale deep ultraviolet (DUV) light sources is required for a wide range of applications such as probing intrinsic fluorescence in a protein, medical equipment/personnel decontamination, and photocatalysis. The external quantum efficiency (EQE) of Light Emitting Diodes (LEDs) operating in the region around 250 nm is still quite low (below 3%). Currently, AlGaN semiconductors are default choice for the DUV light sources. The poor p-type conductivity of Al-rich AlGaN alloys is the major obstacle that limits the EQE of these devices. Significant advances in the EQE of DUV emitters will require the exploitation of disruptive device concepts. This project aims to explore DUV device structures that exploiting new p-type layer strategies to overcome the intrinsic problem of low p-type conductivity in Al-rich AlGaN. The proposed efforts would not only yield breakthroughs in methods for the fabrication of DUV light emitting diodes (LEDs) with improved EQE, but would also lead to technological advancements in novel photonic materials and devices for a range of applications. Through the involvement in the research, students will be trained in the areas of nano-fabrication techniques, material/device design and processing using the state-of-the-art experimental facilities. The project will provide junior researchers with opportunities to participate in conferences and workshops, and gain exposure to the real world applications of DUV photonic devices. Educational activities will also include the integration of undergraduates into research via senior design projects and required project lab courses. Outreach activities include having the PIs serve as mentors of the prestigious Clark Scholars to bring an appreciation of science and technology to highly gifted high school students from around the nation and to increase diversity in science and engineering.
The proposed DUV emitter layer structure is based on hexagonal boron-nitride (hBN) and AlGaN heterostructure bandgap and doping engineering. By implementing the direct wide bandgap and highly conductive hBN p-type layer strategy in nitride DUV emitters, p-type conductivities and DUV transparency of the electron blocking layer and p-type contact layer will be dramatically increased. This will significantly improve the free hole injection and EQE, reduce the operating voltage and heat generation, and increase the device operating lifetime. Control over the p-type electrical resistivity and conductivity type of epitaxial h-BN films will be established by in-situ doping via MOCVD growth. DUV emitter structures incorporating p-type hBN will be grown on sapphire with thick AlN templates to reduce the dislocation density. Ohmic contacts processing including annealing conditions will be optimized. DUV LEDs will be fabricated and their I-V, L-I characteristics, and wall plug efficiency will be correlated with the device structures and fabrication processes.
