RESUMEN
We demonstrate controllable and tunable full color light generation through the monolithic integration of blue, green/yellow, and orange/red InGaN nanowire light-emitting diodes (LEDs). Such multi-color nanowire LED arrays are fabricated directly on Si substrate using a three-step selective area molecular beam epitaxy growth process. The lateral-arranged multi-color subpixels enable controlled light mixing at the chip-level and yield color-tunable light emission with CCT values in the range from 1900 K to 6800 K, while maintaining excellent color rendering capability. This work provides a viable approach for achieving micron and nanoscale tunable full-color LED arrays without the compromise between the device efficiency and light quality associated with conventional phosphor-based LEDs.
RESUMEN
We have examined the carrier injection process of axial nanowire light-emitting diode (LED) structures and identified that poor carrier injection efficiency, due to the large surface recombination, is the primary cause for the extremely low output power of phosphor-free nanowire white LEDs. We have further developed InGaN/GaN/AlGaN dot-in-a-wire core-shell white LEDs on Si substrate, which can break the carrier injection efficiency bottleneck, leading to a massive enhancement in the output power. At room temperature, the devices can exhibit an output power of ~1.5 mW, which is more than 2 orders of magnitude stronger than nanowire LEDs without shell coverage. Additionally, such phosphor-free nanowire white LEDs can deliver an unprecedentedly high color rendering index of ~92-98 in both the warm and cool white regions, with the color rendering capability approaching that of an ideal light source, i.e. a blackbody.
RESUMEN
We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.