| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Low Damage Processing |
| Presenter: | C. Thomas, Tohoku University, Japan |
| Authors: | C. Thomas, Tohoku University, Japan Y. Tamura, Tohoku University, Japan A. Higo, Tohoku University, Japan N. Okamoto, Nara Institute of Science and Technology, 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 the first damage-free top-down process for creating GaAs QDs by combining a high-density bio-template [1] and a neutral beam (NB) etching process [2]. The bio-template consists of a high-density (about 7x1011 cm-2), two-dimensional array of cage-shaped proteins called ferritins with encapsulated metal oxide nanoparticles (NPs). After removal of the protein shell, 7 nm in diameter iron (Fe) or cobalt (Co) 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 thin oxide layer was deposited on top of the single quantum well (GaAs, with Al0.3GaAs barrier layer) samples grown by using metal organic vapor phase epitaxy after removing the native oxide. Then, deposition of the 2D-array etching masks was conducted. An oxygen treatment was carried out to remove the protein shell, followed by a hydrogen radical treatment to remove the remnant oxide layer. Etching was performed using the NB technique. Defect-free nano-pillars [3] were obtained using both etching masks. It appeared that the nano-pillars with Co masks had a better etching profile than those with Fe masks. Indeed, the nano-pillars formed using Co NPs as the etching masks presented a vertical sidewall whereas the ones formed by using Fe NPs presented an etching profile with tapered angles of about 82°. Moreover, we have successfully achieved 15-nm-in-diameter and over 100-nm-high pillars by NBE process. The average height of the nano-pillars was larger when the Co masks were used. These results suggest that the etching selectivity of Co NPs is higher than that of Fe NPs. The maximum density of the nano-pillars was up to 5x1010 cm-2 and did not seem dependent on the chemical nature of the etching mask. The most important parameter for achieving high density, over that of conventional QDs grown by molecular beam epitaxy, is the interaction between the cores and the GaAs surface rather than the etching selectivity. The results showed that III-V compound nanodisk devices can be realized by this defect free top-down nanoprocess.
[1] I. Yamashita et al., Biochim. Biophys. Acta 1800 (2010) 845
[2] S. Samukawa et al., Jpn. J. Appl. Phys. 40 (2001) L997
[3] X. Y. Wang et al., Nanotechnology 22 (2011) 365301.