Site-selective growth of self-assembled InAs quantum dots on focused ion beam patterned GaAs

doi:10.1016/j.physe.2007.09.130

Physica E: Low-dimensional Systems and Nanostructures

Volume 40, Issue 6, April 2008, Pages 2034-2036

https://doi.org/10.1016/j.physe.2007.09.130 Get rights and content

Abstract

A site-selective growth of self-organized InAs quantum dots (QDs) employing a combination of in-situ focused ion beam (FIB) implantation and self-organized molecular beam epitaxy (MBE) growth has been successfully demonstrated. First, a buffer layer of GaAs was grown by MBE before a square lattice of shallow holes with a pitch of 1–2 μm was fabricated by FIB implantation of Ga and In ions. Before InAs deposition, different procedures to remove the implantation damage were tested. The best results were obtained after re-evaporation of 3–5 nm GaAs. Another critical parameter that was carefully optimized is the deposited InAs amount. For the optimized process it was possible to induce growth of single QD in the hole with more than 50% probability. Between the shallow holes of 2 nm depths, no QD growth was observed. The optical quality of positioned dots was investigated by photoluminescence spectroscopy, employing a separate sample where the QDs were overgrown by GaAs cap layer. Excited-state interband transitions up to n=5 were observed from positioned QDs.

Introduction

Self-assembled InAs quantum dots (QDs) have been the subject of intense research over the past decade because of their appealing properties [1]. Currently, these QDs have been utilized for realization of novel nanoelectronic devices [2]. The integration of QDs in such devices requires site-selective growth. Among a variety of schemes for site-controlled nucleation of the dots, the QD growth on substrates patterned with shallow holes employing conventional electron beam lithography has been proven quite successful [3], [4], [5], [6], [7], [8]. Recently, focused ion beam (FIB) technology has also become popular in the fabrication of nanoscale structures [9].

In this work, we present a site-selective growth of molecular beam epitaxy (MBE)-grown InAs QDs on FIB patterned GaAs (1 0 0) substrates. Ga and In ion beams, were employed to pattern a GaAs substrate with shallow holes using post-annealing prior to overgrowth. The influence of the ion dose, the annealing parameters and the deposited InAs amount was studied. Furthermore, photoluminescence (PL) studies on GaAs–capped QDs confirm their good optical quality.

Section snippets

Experimental details

Samples consisting of a 50 nm GaAs layer, 40 periods of a 2 nm AlAs/2 nm GaAs superlattice, and a 300 nm GaAs buffer layer were grown on GaAs(1 0 0) substrates at 600 °C by solid-source MBE. After the growth, the sample was transferred under ultra-high vacuum conditions to an FIB system. A square array of FIB spots covering an area of 60×60 μm² with a pitch of 1–2 μm was fabricated employing two different ion species, Ga and In, respectively. An ion energy of 30 keV was used, and the exposure time of

Results and discussion

After annealing, the shape of the In-implantation-induced patterned holes changes (see Fig. 1). They become elongated along the [0 1 1] direction and their size increases from ∼100 nm diameter to 300×700 nm². The change in its shape may be due to strong material transport during re-evaporation. The depth and diameter of the shallow hole is found to be dose dependent. The QD formation on patterned holes using 1.59 ML of InAs deposition is shown in Fig. 1 for 7.7×10⁴ ions/spot. Here 4–10 QDs/hole are

Summary

We have demonstrated the site-selective growth of QDs on patterned GaAs substrates using FIB implantation of In and Ga ions. For a well-optimized process, it has been possible to locate a single QD in the holes with more than 50% probability without having QD in between. Finally, the PL spectra confirm the good optical quality of site-selective QDs.

Acknowledgment

We acknowledge the financial support by DFG GRK384 and the BMBF via the nanoQuit program.

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Citation Excerpt :
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Site-selective growth of self-assembled InAs quantum dots on focused ion beam patterned GaAs

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Summary

Acknowledgment

J. Cryst. Growth

Physica E

Quantum Dot Heterostructures

Science