One of the grand challenges for future solid-state lighting is the development of high efficiency white light-emitting diodes (LEDs) without using phosphor conversion. In this context, we have investigated the molecular beam epitaxial (MBE) growth and characterization of nanowire LEDs on Si, wherein intrinsic white-light emission is achieved by incorporating self-organized InGaN quantum dots in nearly defect-free GaN nanowires. With the incorporation of the special techniques of p-type modulation doping and electron blocking layer, we have further demonstrated phosphor-free nanowire white LEDs that can exhibit negligible efficiency droop and significantly enhanced internal quantum efficiency (up to ~65%) at room-temperature.Catalyst-free InGaN/GaN nanowire LED heterostructures are grown on Si substrates by MBE. The device active region contains 10 vertically coupled InGaN/GaN quantum dots with In compositions varied in the range of ~10-50% to achieve white-light emission. In addition, each quantum dot layer is modulation doped p-type using Mg. A p-doped AlGaN electron blocking layer is also incorporated between the active region and the p-GaN. Compared to the undoped nanowire LEDs, the p-doped devices can exhibit significantly enhanced internal quantum efficiency (~ 65%) at room-temperature, due to the improved hole injection and transport process. Through detailed studies of the current- and temperature-dependent electroluminescence emission, we have further confirmed that electron overflow can be effectively prevented with the incorporation of a p-doped AlGaN electron blocking layer. The devices can exhibit virtually no efficiency droop for injection current over 1,000 A/cm2. Our studies also show that Auger recombination is not the primary mechanism responsible for efficiency droop in GaN-based nanowire LEDs.  Work is currently in progress to achieve further improved performance by utilizing core-shell-based nanowire heterostructures and by transferring the devices on transparent substrates.

High-efficiency phosphor-free InGaN/GaN nanowire white light-emitting diodes

246th National Meeting (2013)

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