3.5 × 3.5 µm2 GaN blue micro-light-emitting diodes with negligible sidewall surface nonradiative recombination.

Micro-light-emitting diode displays are generating considerable interest as a promising technology for augmented-reality glasses. However, the fabrication of highly efficient and ultra-small ( <3 µm) micro-light-emitting diodes, which are required for augmented-reality applications, remains a major technical challenge due to the presence of strong sidewall nonradiative recombination. In this study, we demonstrate a 3.5 × 3.5 µm2 blue GaN micro-light-emitting diode with negligible sidewall nonradiative recombination compared with bulk nonradiative recombination. We achieve this by using an ultralow-damage dry etching technique, known as neutral beam etching, to create the micro-light-emitting diode mesa. Our 3.5 × 3.5 µm2 micro-light-emitting diode exhibits a low decrease in external quantum efficiency of only 26% at a current density of 0.01 A/cm2, compared with the maximum external quantum efficiency that is reached at the current density of ∼3 A/cm2. Our findings represent a significant step towards realizing micro-light-emitting diode displays for augmented-reality glasses.

Fabrication and Evaluation of N-Channel GaN Metal-Oxide-Semiconductor Field-Effect Transistors Based on Regrown and Implantation Methods.

We have demonstrated the enhancement-mode n-channel gallium nitride (GaN) metal-oxide field-effect transistors (MOSFETs) on homoepitaxial GaN substrates using the selective area regrowth and ion implantation techniques. Both types of MOSFETs perform normally off operations. The GaN-MOSFETs fabricated using the regrowth method perform superior characteristics over the other relative devices fabricated using the ion implantation technique. The electron mobility of 100 cm2/V·s, subthreshold of 500 mV/dec, and transconductance of 14 µs/mm are measured in GaN-MOSFETs based on the implantation technique. Meanwhile, the GaN-MOSFETs fabricated using the regrowth method perform the electron mobility, transconductance, and subthreshold of 120 cm2/V s, 18 µs/mm, and 300 mV/dec, respectively. Additionally, the MOSFETs with the regrown p-GaN gate body show the Ion/Ioff ratio of approximately 4 × 107, which is, to our knowledge, among the best results of GaN-MOSFETs to date. This research contributes a valuable information for the design and fabrication of power switching devices based on GaN.

Enhancement of the evanescent wave coupling effect in a sub-wavelength-sized GaAs/AlGaAs ridge structure by low-refractive-index surface layers.

We have investigated the three-dimensional emission patterns of GaAs/AlGaAs ridge structures with a sub-wavelength-sized top-flat facet by angle-resolved photoluminescence (PL). We found that the integrated PL intensity, and hence the light-extraction efficiency, can be enhanced by about 34% just by covering the ridge surface with a thin SiO2 layer. A double-coupling effect of evanescent waves that occurs at both the semiconductor-SiO2 and SiO2-air interfaces is suggested to be responsible for the improvement, based on a finite-difference time-domain simulation of the electromagnetic field around the ridge top.