Spectroscopic signatures of many-body interactions and delocalized states in self-assembled lateral quantum dot molecules

Abstract

Lateral quantum dot molecules consist of at least two closely-spaced InGaAs quantum dots arranged such that the axis connecting the quantum dots is perpendicular to the growth direction. These quantum dot complexes are called molecules because the small spacing between the quantum dots is expected to lead to the formation of molecular-like delocalized states. We present optical spectroscopy of ensembles and individual lateral quantum dot molecules as a function of electric fields applied along the growth direction. The results allow us to characterize the energy level structure of lateral quantum dot molecules and the spectral signatures of both charging and many-body interactions. We present experimental evidence for the existence of molecular-like delocalized states for electrons in the first excited energy shell.

Coulomb interaction signatures in self-assembled lateral quantum dot molecules

“…In our past work, 18 we observed the Coulomb shift of ensemble and single LQDM PL in both ground and first excited shells under the electric field. The results validate that ground electron and hole states of a LQDM are localized to individual QDs while the first and higher excited electron states are delocalized over the entire LQDM.…”

“…Consequently, we observe a quasicontinuous Stark shift of the PL line as increasing numbers of electrons occupy the excited states. 16,18 To summarize this section, we have provided a detailed understanding of the charging process of LQDMs with nearly degenerate QDs by comparing experimental PL data with theoretical estimates and logical relaxation dynamics. The observation of energy shifts computationally predicted to arise from electron tunneling provides strong experimental evidence for the existence of tunnel coupling for X + (and possibly X − ) in this system.…”

“…The energies of this set of PL lines indicate that the PL emission is from the ground states of the LQDM. 18 Typically, the two QDs, which make up the LQDM, will be slightly different in energy levels. Although we cannot assign PL emission to the right or left QD, we simplify the discussion by always assigning the low-energy PL emission to the right QD and the high-energy PL to the left QD.…”

“…17 Both of these papers predicted sensible signatures of tunnel coupling in charged states. However, the experimental evidence of controllable interdot tunnel coupling in LQDMs [18][19][20][21] remains indirect. The center-to-center distance between a QD pair in a LQDM is about ten times larger than the separation in a VQDM; the tunneling strength is expected to be significantly weaker.…”

Electronic States and Optical Transitions in an Asymmetric Quantum Dot Molecule

“…Redistribution of the energy spectrum and wave functions (WFs) in the QDM leads to dramatic changes in the optical and transport properties of QDMs compared to single QDs [2]. In real growth conditions, the obtained symmetric QDMs are rather rare; more often, due to various physical and technical reasons, grown lateral QDMs are asymmetric [3][4][5]. Similarities between the energy spectra of symmetric molecules (e.g., O 2 , H 2 , or N 2 ) and symmetric QDMs, and, correspondingly, asymmetric molecules (e.g., CO, CO 2 , or NO 2 ) and asymmetric QDMs potentially allow one to design various biochemical sensors and detectors with a single molecule sensitivity [6,7].…”