Polarity Control in AlGaN and Recent Advances in Lateral-polarity-structure Based Optoelectronic and Electronic Devices

AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with the advantages of compact structure, long lifetime, and controllable wavelength, are promising in numerous applications, such as sterilization, detection of biochemical agents and NLOS communication. However, the development of AlGaN-based DUV LEDs faces several challenges, including lacking of carrier localization centers due to fully miscible Al and Ga phases, and strong spontaneous polarization in wurtzite III-nitride crystals herein poor overlap of the electron and hole wavefunctions, both of which lead to low radiative recombination efficiency, jeopardizing device performance. In this work, we talk about two approaches toward the enhancement of quantum efficiency of DUV-LED. First of all, the utilization of miscut sapphire substrates was investigated to obtaining Ga-rich stripes in the active region, resulting in carrier localizations and internal quantum efficiency as high as 90%. Direct evidence on carrier transportation and recombination on step-bunched surface of DUV-LED was provided via conductive AFM. Top view ECCI and cross-sectional HAADF-STEM demonstrated that these current paths are not associated with threading dislocations, but rather are related to the step edges with Ga-rich potential minima. In second part of our work, we take advantage of the opposite polarizations in wurtzite III-nitride crystals, developing a so-called “lateral-polarity-structure“ where III-polar and N-polar domains were simultaneously grown side-by-side on a single wafer. A potential maximum was calculated near the domain boundary via DFT, where hole accumulation could join the efficient radiative recombination, leading to suppressed or even fully-eliminated quantum-confined-stark-effect (QCSE) in the MQWs. This is supported by the RT/LT PL mapping where high IQE value was demonstrated at the domain boundary. A three-dimensional band diagram describing carriers transporting in LPS is proposed for the first time. We believe that LPS platform can efficiently improve radiative recombination, and helps in rational design of future high-efficiency DUV emitters.