Elsevier

Journal of Crystal Growth

Volume 310, Issue 23, 15 November 2008, Pages 5069-5072
Journal of Crystal Growth

InAs/InP QDs with GaxIn1−xAs cap layer by a double-cap procedure using MOVPE selective area growth

https://doi.org/10.1016/j.jcrysgro.2008.08.034Get rights and content

Abstract

GaxIn1−xAs cap layer dependence on self-assembled Stranski–Krastanov (S–K) InAs quantum dots (QDs) was successfully demonstrated using a double-cap procedure and metalorganic vapor phase epitaxy (MOVPE) selective area growth. Selective area growth with a narrow stripe SiO2 mask array pattern was used to control and widen the emission wavelength range of the QDs in a 16-stripe mask array waveguide, and the double-cap procedure was used to improve the uniformity of the QD height. Growth of a 5-layer stacked InAs QD structure was successfully demonstrated using these methods with a Ga0.75In0.25As cap layer.

Introduction

Self-assembled semiconductor quantum dots (QDs) that have zero-dimensional carrier confinement structure are predicted to have unique physical properties [1]. These QDs have recently attracted much attention in terms of both fundamental physics as well as potential device applications. In particular, the application of QDs in 1.55 μm optical telecommunication devices has been shown to be more advantageous than that of conventional quantum well-based devices [2]. Concerning the application of QDs to lasers, one of the problems of self-assembled QDs is low gain due to the small active layer volume. A multiple stacked QD structure is proposed as a solution to this problem.

In our previous study, difficulties were found with an InP first cap layer (FCL) for more than a 3-multi-stacked structure, because of the effect of accumulated strain caused by the lattice mismatch. This is a result of the 3.2% compressive strain that InAs QDs have against an InP substrate. On the other hand, the InP cap layer does not relax the strain; hence the energy of the strain is accumulated by the increasing number of stacked layers. To realize a multi-stacked structure, the cap layer was changed from InP to GaxIn1−xAs. As a result, a 5-layer stacked structure was successfully grown. In this report, we give a comparison of the size and optical properties between two InAs QD samples on InP substrates for different Ga compositions of the GaxIn1−xAs cap layer during the double-cap procedure.

Section snippets

Selective area growth/double-cap procedure

Epitaxial growth was conducted using low-pressure metalorganic vapor phase epitaxy (MOVPE) in a vertical-flow rotating disk reactor system with H2 as the carrier gas. Source materials of trimethyl-indium and triethyl-gallium for group III elements, and tertiarybutyl-arsine and tertiarybutyl-phosphine for group V elements were employed for QD growth.

The QDs were grown via the Stranski–Krastanov (S–K) growth mode. This technique utilizes the lattice mismatch between the substrate and the

Result and discussion

Fig. 3 shows the results of PL measurements at non-masked areas, that is, without the effect of the striped array mask, where the Ga composition of GaxIn1−xAs FCL was x=0.75 (broken line) and x=0.47 (solid line). By changing FCL=InP to GaInAs, As/P exchange could be suppressed at the side of the InAs QDs. The reason for selecting these Ga compositions was that x=0.47 is a lattice match to InP, and x=0.75 could introduce strong tensile strain to the QDs structure in order to relax the total

Conclusion

A 5-layer stacked InAs QD structure was successfully fabricated with a GaxIn1−xAs FCL in the double-cap procedure using MOVPE selective area growth. Higher PL intensity and narrower FWHM were obtained for a Ga composition x=0.75 compared with that for x=0.47. Furthermore, the PL peak wavelength shift of the Ga0.75In0.25As FCL from array no. 1 to 16 was wider than that for the Ga0.47In0.53As FCL, and the InAs QDs in the Ga0.75In0.25As FCL had no degradation in size, even for 5 stacked layers. It

Acknowledgements

This work was supported by a grant-in-aid for Scientific Research (C) #20560334 from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

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