Fabrication of Phosphor-Free III-Nitride Nanowire Light-Emitting Diodes on Metal Substrates for Flexible Photonics.

In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes (LEDs) on copper (Cu) substrates via the substrate-transfer process. Nanowire LED structures were first grown on silicon-on-insulator (SOI) substrates by molecular beam epitaxy. Subsequently, the SOI substrate was removed by combining dry- and wet-etching processes.

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.

Optically Pumped Two-Dimensional MoS2 Lasers Operating at Room-Temperature.

The discovery of direct bandgap semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) has opened a new era in flexible optoelectronic devices. Critical to this development is the realization of a semiconductor laser using the emerging 2D TMDCs. Here, by embedding 2D MoS2 at the interface between a free-standing microdisk and microsphere, we have demonstrated, for the first time, room-temperature lasing from 2D TMDCs.

Engineering the carrier dynamics of InGaN nanowire white light-emitting diodes by distributed p-AlGaN electron blocking layers.

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.

Temperature-dependent nonradiative recombination processes in GaN-based nanowire white-light-emitting diodes on silicon.

In this paper, we have performed a detailed investigation of the temperature- and current-dependent emission characteristics of nanowire light-emitting diodes, wherein InGaN/GaN dot-in-a-wire nanoscale heterostructures and a p-doped AlGaN electron blocking layer are incorporated in the device's active region to achieve white-light emission and to prevent electron overflow, respectively. Through these studies, the Auger coefficient is estimated to be in the range of ∼10(-34) cm(6) s(-1) or less, which is nearly four orders of magnitude smaller than the commonly reported values of planar InGaN/GaN heterostructures, suggesting Auger recombination plays an essentially negligible role in the performance of GaN-based nanowire light-emitting diodes. It is observed, however, that the performance of such nanowire LEDs suffers severely from Shockley-Read-Hall recombination, which can account for nearly 40% of the total carrier recombination under moderate injection conditions (∼100 A cm(-2)) at room temperature.

Controlling electron overflow in phosphor-free InGaN/GaN nanowire white light-emitting diodes.

We have investigated for the first time the impact of electron overflow on the performance of nanowire light-emitting diodes (LEDs) operating in the entire visible spectral range, wherein intrinsic white light emission is achieved from self-organized InGaN quantum dots embedded in defect-free GaN nanowires on a single chip. Through detailed temperature-dependent electroluminescence and simulation studies, it is revealed that electron leakage out of the device active region is primarily responsible for efficiency degradation in such nanowire devices, which in conjunction with the presence of nonradiative surface recombination largely determines the unique emission characteristics of nanowire light-emitting diodes. We have further demonstrated that electron overflow in nanowire LEDs can be effectively prevented with the incorporation of a p-doped AlGaN electron blocking layer, leading to the achievement of phosphor-free white light-emitting diodes that can exhibit for the first time virtually zero efficiency droop for injection currents up to ~2200 A/cm(2).

Power splitters with different output power levels based on directional coupling.

The properties of a wideband photonic crystal power splitter with different output power levels based on directional coupling are investigated numerically with the finite-difference time-domain method. The effects of changing the coupling length and radius of the coupling rods between parallel waveguides on output transmissions are investigated. By further splitting power in each branch a power splitter with four output branches is proposed.