A. Levin

Stark shift in electroluminescence of individual InAs quantum dots

We have fabricated light-emitting-diode heterostructure devices, in which a layer of InAs self-assembled quantum dots is embedded, with an active area of submicron size. In the electroluminescence spectra of these devices, we observed isolated narrow peaks due to emission from individual dots. From the shift of the peaks in an electric field (the quantum confined Stark effect), we show that the ground and excited states in the dots have different spatial alignments of the electron and hole.

Piezoelectric effects in In0.5Ga0.5As self-assembled quantum dots grown on (311)B GaAs substrates

Photocurrent spectroscopy is used to investigate the quantum-confined Stark shift of In0.5Ga0.5As/GaAs self-assembled quantum dots grown on (100) and (311)B planes. By comparing the Stark shift for dots grown on (100) and (311)B planes, we find that in the (311)B dots, the electron and hole wave functions are displaced by a strain-induced piezoelectric field directed from the apex to the base of the dots.

Anisotropy of electronic wave functions in self-assembled InAs dots embedded in the center of a GaAs quantum well studied by magnetotunneling spectroscopy

We present an experimental study of electron wave functions in InAs/GaAs self-assembled quantum dots by magnetotunneling spectroscopy. The electronic wave functions have a biaxial symmetry in the growth plane, with axes corresponding to the main crystallographic directions in the growth plane. Moreover, we observed the in-plane anisotropy of the subbands of the quantum well.

Electrical and optical properties of self-assembled quantum dots

Abstract One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two, i.e. quantum wires (QWi) and quantum dots (QDs), in order to realise novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use self-organised three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. Quantum dots, for example, are believed to provide a promising way for a new generation of optical light sources such as injection lasers. While quantum well structures are already widely used in optoelectronic devices, QWi and QDs appear to be much more difficult to fabricate for this purpose. Some of the electrical and optical properties of self-assembled QDs will be reported in this paper.

Universality of the Stokes Shift for a Disordered Ensemble of Quantum Dots

We present a study of carrier redistribution in InxGa1—xAs/GaAs self-assembled quantum dots (QDs) by comparing electroluminescence (EL) and photocurrent (PC) spectra. We show the existence of a red-shift of the dot emission in EL relative to the dot absorption in PC, referred to as the Stokes shift (SS). The existence of the SS is explained in terms of a thermal redistribution of carriers between dots. According to the thermalization model, the SS increases with the linewidth of the QD absorption spectrum. We show that for a large variety of quantum dots, differing in the material system and/or the growth technique, the SS has a universal dependence on the QD absorption linewidth.

Probing the electronic properties of disordered two-dimensional systems by means of resonant tunnelling

We investigate resonant tunnelling in GaAs/(AlGa)As double-barrier resonant-tunnelling diodes in which a single layer of InAs self-assembled quantum dots is embedded in the centre of the GaAs quantum well. The dots provide a well-defined and controllable source of disorder in the well and we use resonant tunnelling to study the effect of this disorder on the electronic properties of the well.

One-electron spin-dependent transport in split-gate structures containing self-organized InAs quantum dots

The paper presents the results obtained in a study of electron transport in split-gate structures prepared from heterostructures with self-organizing InAs quantum dots situated close to a two-dimensional electron gas. Coulomb oscillations of current through InAs quantum dots depending on the voltage on the gate were observed. Coulomb current oscillations persisted up to about 20 K. The Coulomb energy ΔEC = 12.5 meV corresponding to theoretical estimates for the p-states of quantum dots in our structures was determined.

Spatial mapping of the electron eigenfunctions in InAs self-assembled quantum dots by magnetotunnelling

We use magnetotunnelling spectroscopy as a non-invasive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The images reveal clearly the elliptical symmetry of the ground state and the characteristic lobes of the higher-energy states.

Coulomb oscillations of the current through spin-nondegenerate p states of InAs quantum dots

The electron transport is studied in split-gate structures fabricated on the basis of a modulation-doped heterostructure that contains a single quantum well and self-assembled InAs quantum dots near the 2D electron gas regions. The current passing through the channel with a denumerable set of InAs quantum dots is found to exhibit Coulomb oscillations as a function of the gate voltage. The oscillations are associated with the excited p states of InAs quantum dots, which are characterized by opposite spins and caused by lifting of the spin degeneracy of the p state due to the Coulomb interaction. The Coulomb oscillations of the current are observed up to a temperature of ∼20 K. The Coulomb energy is found to be ΔEc = 12.5 meV, which agrees well with the theoretical estimates for the p states of quantum dots in the structures under study.

Escape of carriers photoexcited in self-organized InAs/GaAs quantum dots

Photocurrent and capacitance spectroscopy are used to investigate a Schottky barrier structure containing a single layer of self-organized InAs/GaAs quantum dots. We show that the temperature dependence of the photocurrent signal from the quantum dots is governed by thermal escape of electrons as the faster carriers.