Vertical alignment of laterally ordered InAs and InGaAs quantum dot arrays on patterned (0 0 1) GaAs substrates

doi:10.1016/S0022-0248(02)01442-2

Journal of Crystal Growth

Volume 242, Issues 3–4, July 2002, Pages 339-344

https://doi.org/10.1016/S0022-0248(02)01442-2 Get rights and content

Abstract

We demonstrate vertical alignment of laterally ordered self-assembled quantum dot (QD) arrays stacked on artificially pre-patterned substrates with two-dimensional hole arrays. The initial InGaAs layer is directly grown on the periodically modulated surface in order to exactly control nucleation sites of QDs to be stacked. After growing three InGaAs dot layers with GaAs spacers as a buffer, laterally ordered InAs dots are grown as an optically active layer. The cross-sectional images of transmission electron microscopy reveal vertical alignment of the stacked QDs. Photoluminescence signal at room temperature is detected from the three-dimensional QD superlattice.

Introduction

Self-assembly is an easy and powerful method to fabricate high-quality quantum dots (QDs) without contamination and defects. These QDs are interesting for fundamental investigations as well as applications such as single electron transistors and QD memories [1], [2]. However, the self-assembling process is governed by statistics, so that QDs nucleate more or less randomly on semiconductor surfaces. This random nucleation makes it difficult to address each individual self-assembled QD. It is a big challenge to reproduce and exactly control the nucleation site of each individual QD. Recently, several groups reported the site control of QDs by overgrowing artificially processed patterns. The patterns were formed with electron beam (EB) lithography, laser holography, and in situ scanning tunneling microscopy [3], [4], [5], [6], [7]. Long-range lateral ordering of InGaAs quantum disks on (3 1 1)B GaAs substrates was reported by Temmyo et al. [6]. But, for any application, the lateral ordering of QDs on (0 0 1) substrates is mandatory. At the same time, it is important to form electrically and optically active QD layers with perfect crystal quality far away from the contaminated interface. Then, the vertical alignment of QDs [8], [9] is a useful technique to transfer the initial surface modulation to the growth front through laterally strain-modulated buffer layer [4], [6], [7]. This buffer layer can consist of a laterally strain-modulated superlattice or stacked self-assembled QDs. Recently, applying the former structure, we have fabricated long-range ordered lines of self-assembled Ge islands on Si substrates [7]. The latter structure would allow us to fabricate a three-dimensionally ordered QD superlattice.

In this letter, we report the fabrication and the characterization of the three-dimensional QD superlattice, which is realized by stacking InAs and InGaAs QD arrays on pre-patterned GaAs (0 0 1) substrates with a two-dimensional surface modulation. Cross-sectional transmission electron microscopy (TEM) reveals vertical alignment of laterally ordered QD arrays, which show good photoluminescence (PL) at room temperature.

Section snippets

Experimental procedure

We have patterned GaAs (0 0 1) substrates with two-dimensional (2D) hole arrays by EB lithography and reactive ion etching. After removing EB-resist by chemical solution, the sample surfaces were further cleaned by irradiation of atomic hydrogen just before the growth [10]. As shown in a schematic diagram of Fig. 1(a), the periodicity of the two-dimensional hole arrays was 200 nm along both [1 0 0] and $[0 1 ̄ 0]$ directions, thus forming a square lattice with a hole density of 2.5×10⁹ cm⁻². The holes

Results and discussion

First, we characterized sample A. In Fig. 2(b), the AFM image reveals perfect periodicity of the two-dimensional QD array over an area of more than 500 nucleation sites. Since the square lattice of the ordered QDs corresponds to that of the hole array pattern, each hole effectively produced each nucleation site for the second InGaAs QD layer through the periodically modulated initial InGaAs layer and the overlying spacer. However, it is noticeable that many nucleation sites are decorated with

Conclusion

We have demonstrated vertical alignment of laterally ordered self-assembled InAs and InGaAs quantum dots grown on patterned GaAs (0 0 1) substrates. The vertical stacking process was analyzed in detail by TEM measurements. Photoluminescence at room temperature was detected from this three-dimensional quantum dot superlattice.

Acknowledgements

The authors thank T. Reindl and W. Winter for technical assistance and M.O. Lipinski and H. Schuler for fruitful discussions.

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Vertical alignment of laterally ordered InAs and InGaAs quantum dot arrays on patterned (0 0 1) GaAs substrates

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusion

Acknowledgements

Phys. Rev. Lett.

Phys. Rev. Lett.

Phys. Rev. Lett.

Phys. Rev. Lett.

Electron. Lett.

Jpn. J. Appl. Phys.

Appl. Phys. Lett.