Size-Dependent Energy Levels of InSb Quantum Dots Measured by Scanning Tunneling Spectroscopy

Abstract

The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the Γ-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials.

Features of the energy spectrum of indium antimonide quantum dots

“…2) imply that, as the QD size decreases, not only the "effective" width of the band-gap will increase, but also the energy distance between the allowed energy levels in the conduction band will increase. Presented in the [8] experimental results for InSb quantum dots with size 3 ± 7 nm confirming these conclusions. Broadening of this kind in real QD occurs due to the finite lifetime of charge carriers caused by spontaneous emission, interaction with phonons, and a number of other processes [9,11].…”

Voltammetry investigation on copper zinc tin sulphide /selenide (CZTSxSe1-x) alloy nanocrystals: Estimation of composition dependent band edge parameters

“…To implement this idea, however valance band (E VB ) and conduction band (E CB ) edges of CZTS x Se 1 À x alloy nanocrystals need to be estimated as a function of 'x'. These parameters in case of quantum dots are generally estimated by ultraviolet photoelectron spectroscopy (UPS) [22] and scanning tunneling spectroscopy(STS) [23,24]. Both these techniques involve major instrumentation and tedious sample preparation and thus out of reach to many chemists for the routine applications.…”

Crossover from quantum to classical transport

“…As expected for a network of finite size (and as discussed in Sec.2.1), the LDOS exhibits a series of sharp peaks, reflecting the presence of discrete energy states (the non-zero energy width of these states arises from the coupling to the leads). This discrete nature of energy levels in nanoscale systems, with a size-dependent energy spacing, has been experimentally observed in metal particles [43], quantum dots [34,35,44] and quantum point contacts [45]. In the right section of Fig.5(a), we have overlain a plot of the network's -curve, i.e., a plot of the total current through the network, , as a function of the voltage .…”