Herein, a successful elimination of the size-dependent efficiency decrease in GaN micro-light-emitting diodes (micro-LEDs) is achieved using damage-free neutral beam etching (NBE). The NBE technique, which can obtain ultralow-damage etching of GaN materials, is used in place of the conventional inductively coupled plasma to form the micro-LED mesa. It is found that all the fabricated micro-LEDs with sizes ranging from 40 to 6 μm show external quantum efficiency (EQE) versus current density characteristics similar to those of large-area GaN LEDs, with a maximum in EQE curves at a current density of as low as about 5 A cm À2 . Furthermore, all the fabricated micro-LEDs, even the 6 μm one, show a similar value of maximum EQE with a variation of less than 10%, clearly indicating a negligible size dependence of emission efficiency of micro-LEDs fabricated by the NBE technique at least down to the size of 6 μm. These results suggest that the NBE process is a promising method of fabricating high-efficiency sub-10 μm GaN
Nanostructuring is the dominant approach for effective thermal conduction control in nanomaterials. In the past decade, researchers have been interested in thermal conduction control by the coherent effects in phononic crystal (PnC) systems. Recent theoretical works predicted that nanopillars on the surface of silicon membranes could cause a dramatic thermal conductivity reduction due to the phonon local resonances. However, this remarkable prediction has not been experimentally verified yet with the deep-nanoscale pillar-based PnCs. Here, we fabricate nanopillars on suspended silicon membranes using damageless neutral-beam etching and investigate the impact of nanopillars on the thermal conductivity of the membranes in the 4–300 K range. We found that thermal conductivity reduction caused by the nanopillars does not exceed 16%, which is much weaker than that predicted by the theoretical works. Moreover, this reduction remains temperature independent. These facts make the coherence an unlikely reason for the observed reduction. Indeed, our Monte Carlo simulations can reproduce the experimental results under a purely incoherent approximation. Our study shows that the coherent control of heat conduction by PnC nanostructures is more challenging to observe experimentally in reality than predicted in near-ideal modeling.
This study reports the fabrication of the high-quality hafnium dioxide (HfO2) film at room temperature (20–30 °C) using the neutral beam enhanced atomic layer deposition (NBEALD) we developed. The HfO2 film was fabricated using tetrakis(ethylmethylamino)hafnium (TEMAH) as the Hf precursor and O2 NB as the oxidant. Argon gas was used for the carrier and purge gases. The HfO2 film-deposition process consists of 5-s TEMAH feed, 5-s Ar purge, 5-s O2 gas injection, 20-s O2 neutral beam irradiation, and 5-s Ar purge. The HfO2 film exhibited a saturated growth per cycle of 0.18 nm/cycle and a high-quality film with low C contamination (2.7%), N contamination (3.9%), and a good O/Hf ratio (2.0) was achieved. The film also had an ideal refractive index of 1.9. Additionally, continuously grown high-quality HfO2 and silicon dioxide (SiO2) gate oxide films (stacked HfO2/SiO2 gate oxide film) were successfully fabricated at room temperature. This film has the potential to decrease the thermal budget, thus enabling high flexibility when designing semiconductor structures. These findings demonstrate the effectiveness of our NBEALD in forming high-k gate stack structures.
In case of using pure chlorine chemistry, Ge etching reactivity is three times higher than Si etching reactivity because of the larger lattice spacing in Ge. As a result, during the chlorine plasma etching of a Ge Fin structure, there are serious problems such as a large side-etching and large surface roughness on the Ge sidewall. Conversely, the authors found that several-ten nanometer-width Ge Fin structures with defect-free, vertical, and smooth sidewalls were successively delineated by chlorine neutral beam etching. Based on these results, the problems caused by chlorine plasma etching are considered to be due to the enhancement of chemical reactivity caused by defect on the sidewall with the irradiation of ultraviolet/vacuum ultra violet (UV/VUV) photons. Namely, it is clarified that the neutral beam etching could achieve real atomic layer etching by controlling the defect without any UV/VUV photons on the sidewall surface for future nanoscale Ge Fin structures.
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