| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Plasma Processing of Nanoparticles and Nanomaterials |
| Presenter: | Cédric Thomas, Tohoku University, Japan |
| Authors: | C. Thomas, Tohoku University, Japan K. Yoshikawa, Tohoku University, Japan C.Y. Lee, Tohoku University, Japan Y. Tamura, Tohoku University, Japan A. Higo, Tohoku University, Japan T. Kiba, Hokkaido University, Japan A. Murayama, Hokkaido University, Japan I. Yamashita, Nara Institute of Science and Technology, Japan S. Samukawa, Tohoku University, Japan |
| Correspondent: | Click to Email |
Quantum dot (QD) lasers have been extensively studied in the last few decades due to their device characteristics benefits. However, fabrication of a high density and uniform two-dimensional array of QDs is still a big challenge. We have developed a damage-free top-down process for creating InGaAs QDs by combining a high-density bio-template [1] and a neutral beam (NB) etching process [2]. The bio-nano process consists of a high-density (up to 7x1011 cm-2), two-dimensional array of cage-shaped proteins called ferritins with encapsulated metal oxide nanoparticles (NPs). Ferritins can be functionalized with polyethylene glycol (PEG) to control distance between them and avoid QDs in-plane coupling. After removal of the protein shell, 7 nm in diameter iron oxide NPs were used as etching masks. The NB etching consists of an inductively coupled plasma chamber separated from the process chamber by a carbon electrode with a high-aspect-ratio aperture array. As a result, the charged particles are efficiently neutralized whereas almost no UV photons can reach the sample.
A self-assembled monolayer of PEG-ferritins was formed by spin coating on a GaAs cap surface with native oxide. Samples grown by metalorganic vapor phase epitaxy (MOVPE) with the following structure were used: 10-nm-thick GaAs cap, three 8-nm-thick In0.24Ga0.76As active layers separated by two 20-nm-thick GaAs barrier layers on top of a semi-insulating substrate. A low-temperature oxygen annealing in vacuum was used to remove protein shell and form etching mask with the iron oxide cores. Subsequently, a hydrogen radical treatment was performed during 30 min at 350°C to remove native oxide, followed by hydrogen passivation at room temperature. Nanopillars were etched by neutral beam etching process with a mixture of argon and chlorine. Substrate temperature, neutrals energy and mixture ratio were investigated to find the optimized conditions in term of etching profile and nanopillars density. It has been found that a mixture ratio of Ar:Cl2 = 27:73 with a substrate temperature of 50°C were the best conditions to obtain high-density and anisotropic nanopillars, with diameters about 20 nm and height about 80 nm. After regrowth of the GaAs barrier layer by MOVPE, photoluminescence was observed. PL emission from InGaAs QDs could be detected. The results showed that III-V compound QDs can be realized by this damage free top-down nanoprocess.
[1] I. Yamashita et al., Biochim. Biopys. Acta 1800 (2010) 845
[2] S. Samukawa et al., Jpn J. Appl. Phys. 40 (2001) L997