Ground-state interband transition of individual self-assembled InAs/Al0.6Ga0.4As quantum dots observed by scanning-tunneling-microscope light-emission spectroscopy

Abstract

We have investigated the optical transitions in individual self-assembled InAs/Al0.6Ga0.4As quantum dots (QDs) by means of scanning-tunneling-microscope (STM) light-emission spectroscopy. Localized bright features were observed in the spectrally resolved light intensity images measured by injecting electrons from the STM tip. The light emission spectra measured over the bright features showed single emission peaks having different peak energies with linewidths of 30–45 meV. By comparing these results with atomic-force-microscope images and photoluminescence (PL) spectra, we have identified the bright features with the ground-state interband transition from individual InAs QDs. The emission peak energies were compared with the transition energies calculated for pyramidal-shaped QD structures, based on a single-band and constant-confining-potential model. A reasonable agreement was obtained between the experimental and calculated results. The emission linewidth of individual dots is much narrower than the linewidth (∼200 meV) measured by PL from an ensemble of dots. This fact demonstrates the importance of measuring the linewidth for individual dots rather than for an ensemble of dots with size distribution.

Quantification of the size-dependent energy gap of individual CdSe quantum dots by valence electron energy-loss spectroscopy

“…This knowledge is usually derived from methods, which do not show the spatial resolution necessary to probe individual nanoparticles smaller than about 10 nm, or which lack the possibility to simultaneously measure the size of sub-10 nm particles and to correlate the electronic properties with the spatial information. Scanning-tunneling-microscope (STM) luminescence and STM light-emission spectroscopy [3,19,20], and photoluminescence scanning nearfield optical microscopy (SNOM) can be used to measure the energy gap of individual quantum dots [21,22]. However, the spatial resolution of these methods does not allow for measuring the size of small particles, i.e.…”

Scanning Tunneling Luminescence of Individual CdSe Nanowires

“…STL studies have been intensively performed on the luminescence in III/V semiconductor heterostructures, wherein quantum wells,3–5 quantum wires6, 7 or quantum dots8–10 are embedded in a larger‐bandgap material to achieve carrier confinement. In contrast, there are only a few reports on STM‐induced light emission from freestanding semiconductor nanostructures deposited on a metal substrate 11–13.…”