Time-resolved cathodoluminescence of InGaAs/AlGaAs tetrahedral pyramidal quantum structures

Abstract

An original time resolved cathodoluminescence set up has been used to investigate the optical properties and the carrier transport in quantum structures located in InGaAs/AlGaAs tetrahedral pyramids. An InGaAs quantum dot formed just below the top of the pyramid is connected to four types of low-dimensional barriers: InGaAs quantum wires on the edges of the pyramid, InGaAs quantum wells on the (111)A facets and segregated AlGaAs vertical quantum wire and AlGaAs vertical quantum wells formed at the centre and at the pyramid edges. Experiments were performed at a temperature of 92 K, an accelerating voltage of 10 kV and a beam probe current of 10 pA. The cathodoluminescence spectrum shows five luminescence peaks. Rise and decay times for the different emission wavelengths provide a clear confirmation of the peak attribution (previously done with other techniques) to the different nanostructures grown in a pyramid. Moreover, experimental results suggest a scenario where carriers diffuse from the lateral quantum structures towards the central structures (the InGaAs quantum dot and the segregated AlGaAs vertical quantum wire) via the InGaAs quantum wires on the edges of the pyramid. According to this hypothesis, we have modeled the carrier diffusion along these quantum wires. An ambipolar carrier mobility of 1400 cm 2 /V s allows to obtain a good fit to all temporal dependences.PACS 78.67.-n IntroductionA complete characterization of a nanostructure involves the investigation of its structural, electronic and optical properties. Different experimental tools for testing the structure of a quantum dot (QD) or a quantum wire (QWR) are employed. We might cite direct imaging methods, such as scanning tunnelling microscopy (STM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) [1]. STM and AFM have in principle atomic resolution and, as well as SEM, are able to reveal directly the morphology of a surface. TEM is used to inspect a nanostructure embedded in its nano-environment. Electronic and optical properties of a single nanostructure are mainly studied with spectroscopic tools. Existing local luminescence probe techniques are [2]: spatially localized micro-photoluminescence spectroscopy (µ-PL) using either strong focusing or masking; near-field optical microscopy (SNOM) to avoid the diffraction limitation of far-field optics; cathodoluminescence (CL), using focused energetic electrons in an electron microscope; and scanning tunneling luminescence (STL), using low-energy electrons injected or extracted from the tip of a STM.When combined with picosecond or femtosecond laser pulses, spectroscopic techniques allow for studying the carriers dynamics in a semiconductor sample. Phenomena as different as carrier capture, energy relaxation, radiative recombination or carrier transport are then accessible [3].In this article we employ an original time resolved cathodoluminescence (TRCL) set-up to investigate the time resolved luminescence of quantum structures ...

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