Electronic structure of atomically coherent square semiconductor superlattices with dimensionality below two

Abstract

The electronic structure of recently synthesized square superlattices with atomic coherence composed of PbSe, CdSe, or CdTe nanocrystals (NCs) attached along {100} facets is investigated using tight-binding calculations. In experimental realizations of these systems [W. H. Evers et al., Nano Lett. 13, 2317], NC facets are atomically bonded, resulting in single-crystalline sheets, which, due to their nanogeometry, have an effective dimensionality below two. We predict electronic structures composed of successive bands formed by strong coupling between the wave functions of nearest-neighbor NCs. This coupling is mainly determined by the number of atoms at the NC bonding plane. The band structures deviate markedly from that of the corresponding two-dimensional (2D) quantum well; the 2D case can be recovered, however, if the effects of the nanogeometry are gradually reduced. The width of the bands can reach hundreds of meV, ascribing highly promising transport properties to square superlattices. The band edges are located at k = 0 except for PbSe superlattices, where their position in k space surprisingly depends on the parity of the number of {100} atomic planes in the NCs. Our calculations demonstrate that semiconductors with dimensionality below two have a strong potential for (opto-)electronic, photovoltaic, and spintronic applications.

Hybrid Growth Modes of PbSe Nanocrystals with Oriented Attachment and Grain Boundary Migration

“…[15,16] Since NCs with different growth modes normally show different physical and chemical properties, detailed investigations on NCs growth processes may help better understand the phase transformation and the underlying growth mechanisms. [18] Oriented attachment mainly consists of the following three steps: (1) adjacent particles spontaneously self-organize so that they share a common crystallographic orientation; (2) the particles fuse to create a planar coherent interface; (3) the primary particles are perfectly aligned during growth, [14,19] as implied by the diffraction of a single crystal structure. [18] Oriented attachment mainly consists of the following three steps: (1) adjacent particles spontaneously self-organize so that they share a common crystallographic orientation; (2) the particles fuse to create a planar coherent interface; (3) the primary particles are perfectly aligned during growth, [14,19] as implied by the diffraction of a single crystal structure.…”

Epitaxially Connected PbSe Quantum-Dot Films: Controlled Neck Formation and Optoelectronic Properties

“…According to Kalesaki et al, the bandwidth of 1S e minibands in 2D cubic PbSe QD superlattices with initial QDs of 6 nm in diameter increases approximately linearly from ∼80 to ∼120 meV as the number of atoms in the neck increases from ∼60 to ∼110. 41 The neck widths we observe correspond to between ∼49 and ∼85 atoms in the neck. We do indeed observe significant broadening of the first exciton peak in the absorption spectrum for treatments that induce necking.…”

Exciton Transfer in Array of Epitaxially Connected Nanocrystals

“…The opposite case t e,h 2α∆ e,h , when electrons and holes are delocalized in the NC array was studied in Refs. [40][41][42] .…”