INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 39 (2006) 4940–4947 doi:10.1088/0022-3727/39/23/007 Different regimes of electronic coupling and their influence on exciton recombination in vertically stacked InAs/InP quantum wires David Fuster 1,2 , Juan Mart´ ınez-Pastor 1 , Luisa Gonz ´ alez 2 and Yolanda Gonz´ alez 2 1 Instituto de Ciencia de los Materiales, Universidad de Valencia, PO Box 22085, 46071 Valencia, Spain 2 Instituto de Microelectr ´ onica de Madrid (CNM-CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain E-mail: david.fuster@uv.es Received 28 June 2006, in final form 4 September 2006 Published 17 November 2006 Online at stacks.iop.org/JPhysD/39/4940 Abstract In the present work we study the influence of stacking self-assembled InAs quantum wires (QWRs) on the emission wavelength and the excitonic recombination dynamics. The reduction in the InP spacer layer thickness, d (InP), produces both a size filtering effect towards large wire ensembles and an increase in the vertical coupling for electrons and holes along the stack direction. The different vertical coupling for electrons and holes induces a different behaviour in the exciton recombination dynamics, depending on the InP spacer layer thickness: weak electron coupling and negligible hole coupling for d (InP) > 10 nm, intermediate electron coupling and weak hole coupling for 5 nm  d (InP)  10 nm and strong electron coupling and moderate hole coupling for d (InP) < 5 nm. Such exciton dynamics have been established by comparing the experimental time decay results with a multi-quantum well model accounting for the vertical carrier coupling. 1. Introduction The incorporation of quantum nanostructures in the active region of semiconductor laser diodes enhances the gain and decreases the threshold current, as predicted by Arakawa and Sakaki [1]. These advantages can be achieved by improving the size distribution of the nanostructures ensembles. A demonstrated way to do it is to fabricate vertical stacks of self- assembled quantum nanostructures [2–10]. Good knowledge of the electronic and optical properties of stacked multi-layer structures is necessary to use them in optoelectronic devices, particularly in laser diodes. The nanostructures stacked in multilayers exhibit a ver- tical correlation (that is, they are piled up vertically aligned along the growth direction), depending on the spacer layer thickness and also related to the size of the buried nanostruc- ture [2, 4, 5, 7–10]. This effect is due to the propagation of an inhomogeneous strain field produced by the buried nanos- tructures towards the capping layer surface. This vertical cor- relation would be responsible for a self-filtering effect on the average size of the nanostructures within the vertical stack [3, 7, 8], leading to an improvement in the whole size dis- tribution. Furthermore, the spacer layer thickness between stacked layers also affects the average size [8], and even al- lows an electronic coupling if the spacer thickness becomes sufficiently small [2, 6, 11–13]. If the self-filtering effect is towards small (large) sizes a blue (red) shift of the photolumi- nescence (PL) spectrum is measured [6–9], whereas a redshift of the PL spectrum is observed when the electronic coupling in- creases [2, 7, 11, 12]. A simultaneous and more important con- sequence of such electronic coupling is the exciton wavefunc- tion delocalization along the growth direction [6, 11, 14–17]. The properties of laser diodes based on this kind of stacked lay- ers can be negatively modified by the above-described effects. 0022-3727/06/234940+08$30.00 © 2006 IOP Publishing Ltd Printed in the UK 4940