Stark spectroscopy and radiative lifetimes in single self-assembled CdTe quantum dots

Abstract

International audienceWe present studies on Coulomb interactions in single self-assembled CdTe quantum dots. We use a field effect structure to tune the charge state of the dot and investigate the impact of the charge state on carrier wave functions. The analysis of the quantum confined Stark shifts of four excitonic complexes allows us to conclude that the hole wave function is softer than electron wave function; i.e., it is subject to stronger modifications upon changing of the dot charge state. These conclusions are corroborated by time-resolved photoluminescence studies of recombination lifetimes of different excitonic complexes. We find that the lifetimes are notably shorter than expected for strong confinement and result from a relatively shallow potential in the valence band. This weak confinement facilitates strong hole wave function redistributions. We analyze spectroscopic shifts of the observed excitonic complexes and find the same sequence of transitions for all studied dots. We conclude that the universality of spectroscopic shifts is due to the role of Coulomb correlations stemming from strong configuration mixing in the valence band

Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures

“…Although, for dot in Fig. 1a if we assume that p ind ≈ 8 nm, we get the dipole moment for the direct exciton p dir = 1.1 nm, which is a value comparable with reported p for InAs and CdTe QDs [4,6] and also smaller than QD height. In Fig.…”

“…Application of a bias results in an electric field given by a capacitor formula: F = (U − U bi )/l, where U and U bi are the applied and built-in voltage, respectively, and l is the width of the intrinsic region of our device. With increasing the electric field, PL lines shift due to the quantum confined Stark effect described by E(F ) = E(0) + pF + βF 2 , where E(0) is the transition energy at zero electric field, p and β are dipole moment and exciton polarizability, respectively [4]. We observe two transitions: one weakly (X 1 ) and one strongly (X 2 ) shifting with bias.…”

“…Let us note that both orientations are possible regardless of the exciton emission energies. Different p values may result from transitions from different QDs or different QD excitonic complexes [4,6]. We identify transitions with |p| substantially larger than 1 Å as indirect excitons, i.e.…”

Optical study of electron-electron exchange interaction in CdTe/ZnTe quantum dots

“…8,[14][15][16] The PL spectrum of a single randomly selected QD [presented in Fig 1(a)] consists of a number of sharp emission lines originating from recombination of different excitonic complexes. Due to the high efficiency of single carrier capture under nonresonant excitation 14 , we observe emission lines related to the transitions of excitons of various charge states.…”

Correlative Optical Spectroscopy and Atom Probe Tomography

“…(a) Potential profile and confined electron and hole energies and wave functions in a rectangular quantum well exhibiting the buildup of an internal field -the term E e,h refers to a zero-field system; (b) study of the quantum confined Stark effect in GaN/AlN quantum discs embedded in a nanowire and with hetero-interfaces defined on the polar (0001) planes -a STEM micrograph of the nanowire heterostructure is reported in the inset; the plot shows the dependence of the cathodoluminescence emission energies on the quantum disc monolayer (ML) thickness, with the blue line indicating the predicted values if no field was present (Adapted from [19]). (c) Potential profile and confined electron and hole energies and wave functions in a rectangular quantum well across which an external field is applied; (d) study of a CdSe/ZnSe quantum dot embedded in a Schottky junction -the scheme is reported in the inset; the plot shows dependence of the PL emission energy on the electric field applied to the junction (Adapted from [20]). Fig.…”