Magnetophotoluminescence of stacked self-assembled InP quantum dots

Abstract

We report magnetophotoluminescence measurements of stacked layers of self-assembled InP quantum dots. With a magnetic field applied in the growth direction we have determined the exciton reduced mass from the field dependence of the photoluminescence energy. By applying a magnetic field perpendicular to the growth direction, we have analyzed the spatial confinement of the dots in the growth direction. We observe a large increase in the shift of the exciton energy between 0 and 50 T when the thickness of the GaInP spacer layer between the dots is reduced from 8 to 4 nm. This indicates a decrease in spatial confinement in the growth direction which we attribute to strong electronic coupling between vertically stacked dots.During the last few years much effort has been put into the study of self-assembled semiconductor quantum dots ͑QDs͒, due to their promising optical and electrical properties for applications such as lasers. 1 Photoluminescence ͑PL͒ measurements on these QDs reveal an intense emission of visible ͑InP͒ 2-4 or infrared ͓In͑Ga͒As, 1,5-9 InSb, 10 and InAlAs͔ 11 light, with linewidths of the order of 40 meV, from the confined excitons in the dots. These rather broad lines are caused by the luminescence of large amounts of QDs, ϳ10 10 cm Ϫ2 , with a typical 10% size nonuniformity. On the other hand, by repeating layers of dots separated by a few nanometers a vertical alignment occurs giving a reduction in the linewidth due to a more homogeneous size distribution and electronic coupling. 3,5,6 Here we present PL measurements of stacked InP QDs in magnetic fields up to 50 T. Our data show that reducing the thickness of the GaInP barrier between layers of dots results in strong electronic coupling between vertically stacked InP dots. The control of the electronic coupling of QDs offers the potential for wavefunction engineering, which is interesting, not only for fundamental physics, 12 but also for laser applications. Indeed, the first injection laser based on stacked InP quantum dots has recently been reported. 13 The InP quantum dots were grown by solid-source molecular beam epitaxy on a GaAs substrate with a GaAs buffer layer, and embedded in a Ga 0.52 In 0.48 P waveguide layer. The lattice mismatch between the InP and the Ga 0.52 In 0.48 P is 3.7%. For sample A, only one layer of dots was grown by depositing nominally 3 ML of InP. For samples B, C, and D three layers of InP dots were grown, separated by GaInP spacer layers with nominal thicknesses of 8, 4, and 2 nm, respectively. A detailed description of these samples can be found elsewhere. 3 Cross-sectional transmission electron microscopy ͑TEM͒ pictures show that for samples B, C and D the InP QDs are nicely stacked above each other. 3 The dots have typical dimensions of 16 nm diameter and about 2 nm height, with a density of 5ϫ10 10 cm Ϫ2 per layer. The PL experiments were performed at 4.2 K in pulsed magnetic fields up to 50 T, applied parallel and perpendicular to the growth direction, z. The excitation was provided by a continuous wave frequen...

Magneto-optical properties of stacked self-assembled InAs quantum dots

“…Roughly speaking, the dependence of the central peak position of the QDs line with B shows two different regimes. 6,7 If the magnetic length lϭͱប/eB is larger than the transverse extension of the exciton wave function ϭͱ͗⌿͉x 2 ϩy 2 ͉⌿͘, the magnetic field produces a diamagnetic shift ⌬Eϭe 2 ͗⌿͉x 2 ϩy 2 ͉⌿͘B 2 /8, where is the exciton reduced mass. In sufficiently large magnetic fields, the magnetic length can become smaller than the exciton radius and the magnetic confinement, rather than the spatial confinement of the excitons, dominates.…”

Pulsed magnetic fields as a probe of self-assembled semiconductor nanostructures

“…Further details may be found in Refs. [2][3][4][5][6][7]9]. All experiments discussed herein were conducted at 4:2 K with the field perpendicular to the plane of the samples.…”

“…[1]). Initial work was focused on InP self-assembled quantum dots (QDs) in GaInP 2 [2,3], but has recently expanded to include InAs QDs in GaAs [4,5], GaSb QDs in GaAs [6] and InAs quantum wires in InP [7].…”

Room-temperature lasing via ground state of current-injected vertically aligned InP/GaInP quantum dots

“…The dots are vertically aligned and are electronically coupled as described earlier. 11,12 The dot density is 5 ϫ10 10 cm Ϫ2 . The stack is inserted in the middle of a 145-nm-thick Ga 0.52 In 0.48 P waveguide.…”