Full-Color Single Nanowire Pixels for Projection Displays

Multicolor single InGaN/GaN dot-in-nanowire light emitting diodes (LEDs) were fabricated on the same substrate using selective area epitaxy. It is observed that the structural and optical properties of InGaN/GaN quantum dots depend critically on nanowire diameters. Photoluminescence emission of single InGaN/GaN dot-in-nanowire structures exhibits a consistent blueshift with increasing nanowire diameter. This is explained by the significantly enhanced indium (In) incorporation for nanowires with small diameters, due to the more dominant contribution for In incorporation from the lateral diffusion of In adatoms. Single InGaN/GaN nanowire LEDs with emission wavelengths across nearly the entire visible spectral were demonstrated on a single chip by varying the nanowire diameters. Such nanowire LEDs also exhibit superior electrical performance, with a turn-on voltage ∼2 V and negligible leakage current under reverse bias. The monolithic integration of full-color LEDs on a single chip, coupled with the capacity to tune light emission characteristics at the single nanowire level, provides an unprecedented approach to realize ultrasmall and efficient projection display, smart lighting, and on-chip spectrometer

Breaking the Transverse Magnetic-Polarized Light Extraction Bottleneck of Ultraviolet‑C Light-Emitting Diodes Using Nanopatterned Substrates and an Inclined Reflector

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (UV-C) spectral range (210–280 nm) exhibit extremely low external quantum efficiency, primarily due to the presence of large threading dislocations and extremely low transverse magnetic (TM) light extraction efficiency. Here, we have demonstrated that such critical issues can be potentially addressed by using AlGaN quantum-well heterostructures grown on a hexagonal nanopatterned sapphire substrate (NPSS) and a flip-chip-bonded inclined Al mirror. Our finite-difference time domain-based numerical analysis confirms that the maximum achievable efficiency is limited by the poor light extraction efficiency due to the extremely low TM-polarized emission. In our experiment, with the usage of a meticulously designed hexagonal NPSS and an inclined Al side wall mirror (>90% reflective in the UV-C wavelength), the AlGaN quantum-well UV-C LEDs showed nearly 20% improvement in the light output power and efficiency compared to the conventional flat flip-chip LEDs. The UV-C LEDs operating at ∼275 nm exhibit a maximum output power of ∼25 mW at 150 mA, a peak external quantum efficiency of ∼4.7%, and a wall plug efficiency of ∼3.25% at 15 mA under continuous wave (CW) conditions. The presented approach opens up new opportunities to increase the extraction of UV light in the challenging spectral range by using properly designed patterned substrates and an engineered Al reflector

Breaking the Transverse Magnetic-Polarized Light Extraction Bottleneck of Ultraviolet‑C Light-Emitting Diodes Using Nanopatterned Substrates and an Inclined Reflector

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (UV-C) spectral range (210–280 nm) exhibit extremely low external quantum efficiency, primarily due to the presence of large threading dislocations and extremely low transverse magnetic (TM) light extraction efficiency. Here, we have demonstrated that such critical issues can be potentially addressed by using AlGaN quantum-well heterostructures grown on a hexagonal nanopatterned sapphire substrate (NPSS) and a flip-chip-bonded inclined Al mirror. Our finite-difference time domain-based numerical analysis confirms that the maximum achievable efficiency is limited by the poor light extraction efficiency due to the extremely low TM-polarized emission. In our experiment, with the usage of a meticulously designed hexagonal NPSS and an inclined Al side wall mirror (>90% reflective in the UV-C wavelength), the AlGaN quantum-well UV-C LEDs showed nearly 20% improvement in the light output power and efficiency compared to the conventional flat flip-chip LEDs. The UV-C LEDs operating at ∼275 nm exhibit a maximum output power of ∼25 mW at 150 mA, a peak external quantum efficiency of ∼4.7%, and a wall plug efficiency of ∼3.25% at 15 mA under continuous wave (CW) conditions. The presented approach opens up new opportunities to increase the extraction of UV light in the challenging spectral range by using properly designed patterned substrates and an engineered Al reflector