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To identify the individually optimized thermal annealing conditions for reducing the contact resistivity between highly Ga-doped ZnO (GaZnO) and doped-GaN and for improving the electrical and optical properties of GaZnO, the results of the one-step and two-step growth/annealing processes of GaZnO at various growth and thermal annealing temperatures are compared. The one-step (two-step) process corresponds to the condition of thermal annealing for the whole GaZnO layer (only for a 10-nm GaZnO layer of the first-step growth). The two-step process always results in lower contact resistivity on either p-GaN or n-GaN at any annealing temperature. Lateral and vertical light-emitting diodes (LEDs) with GaZnO layers on the top are fabricated to show that the LED samples with the two-step process have the lower device resistance levels, higher emission efficiencies, and weaker efficiency droop effects, when compared with those with the one-step process. In the lateral LED sample with the two-step process, the combination of the effective atomic interdiffusion at the GaZnO/p-GaN junction under the optimized annealing condition and the preservation of the superior electrical property in the major GaZnO layer without annealing leads to its better performance, when compared with that of the lateral LED sample with the one-step process. [ABSTRACT FROM AUTHOR]

The enhancement of the modulation bandwidth (MB) of a light-emitting diode (LED) by reducing its mesa size, decreasing its active layer thickness, and inducing surface plasmon (SP) coupling with its quantum well (QW) is illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-GaN surface, Ga-doped ZnO current-spreading layer, and Ag nanoparticles for inducing SP coupling. In a single-QW LED with a circular mesa of 10~\mu \textm in radius, SP coupling leads to a record-high LED MB of 528.8 MHz in the visible range. A smaller RC time constant can generally lead to a higher MB. However, when the RC time constant is smaller than $\sim 0.2$ ns, its effect for increasing MB saturates. The results also confirm that the MB is essentially proportional to the square roots of carrier decay rate and injected current density. [ABSTRACT FROM PUBLISHER]

By increasing the Mg-doping level and hence the hole concentration in the p-AlGaN electron-blocking layer (EBL), particularly around the interface between the EBL and the top quantum barrier (QB), of a light-emitting diode (LED), the polarization field in this layer can be screened for reducing the potential barrier of hole and hence enhancing the hole-tunneling efficiency such that the overall LED emission efficiency is increased. The increase of Mg-doping level is implemented based on an Mg preflow growth technique, in which Mg source is supplied into the metalorganic chemical vapor deposition chamber for several minutes before the growth of p-AlGaN or p-GaN. It is found that by increasing the Mg-doping level by ~20 times near the interface between the EBL and the top QB, LED emission intensity can be enhanced by ~9.4 times. Based on a simulation study, we observe that the energy difference between the valence band edge and the quasi-Fermi level of hole in the EBL is reduced by increasing the Mg-doping level in this layer such that the total hole density in the quantum wells is increased for enhancing the LED emission efficiency. [ABSTRACT FROM PUBLISHER]

p-GaN/u-GaN alternating-layer nanostructures are grown with molecular beam epitaxy to show a low p-type resistivity level of $0.038~\Omega $ -cm. The obtained low resistivity is due to the high hole mobility in the u-GaN layers, which serve as effective transport channels of holes diffused from the neighboring p-GaN layers. The Mg doping in a thin p-GaN layer can lead to a high Mg-doping concentration for supplying holes to the neighboring u-GaN layers. Simulations based on a 1-D drift diffusion charge control model and the Brooks–Herring theory of ionized impurity scattering are undertaken to first obtain the depth-dependent distributions of hole concentration, mobility, and, hence, resistivity. Then, weighted averaging processes are used for evaluating the effective hole concentration, mobility, and resistivity of a p-GaN/u-GaN alternating-layer nanostructure to give consistent results with the measured data. [ABSTRACT FROM AUTHOR]