Coexistence and Coupling of Zero-Dimensional, Two-Dimensional and Continuum Resonances in Nanostructures
Quantum dots (QDs) embedded in a matrix exhibit a coexistence of 'zero-dimensional' (0D) bound electron and hole states on the dot with 'three-dimensional' (3D) continuum states of the surrounding matrix. In epitaxial QDs one encounters also 'two-dimensional' (2D) states of a quantum well-like supporting structure (wetting layer). This coexistence of 0D, 2D, and 3D states leads to interesting electronic consequences explored here using multiband atomistic pseudopotential calculations. We distinguish strained dots (InAs in GaAs) and strain-free dots (InAs in GaSb) finding crucial differences: in the former case 'potential wings' appear in the electron confining potential in the vicinity of the dot. This results in the appearance of localized electronic states that lie above the threshold of the 3D continuum. Such resonances are 'strain-induced localized states' (SILSs) appearing in strained systems, whereas in strain-free systems the dot resonances in the continuum are the usual 'virtual bound states' (VBSs). The SILSs were found to occur regardless of the thickness of the wetting layer and even in interdiffused dots, provided that the interdiffusion length is small compared to the QD size. Thus, the SILSs are well isolated from the environment by the protective potential wings, whereas the VBSs are strongly interacting. These features are seen in our calculated intraband as well as interband absorption spectra. Furthermore, we show that the local barrier created around the dot by these potential wings suppresses the 0D-2D (dot-wetting layer) hybridization of the electron states. Consequently, in contrast to findings of simple model calculations of envelope function, 0D-to-2D 'crossed transitions' (bound hole-to-wetting layer electron) are practically absent because of their spatially indirect character. On the other hand, since no such barrier exists in the hole confining potential, a strong 0D-2D hybridization is present for the hole states. We show this to be the source for the strong 2D-to-0D crossed transitions determined experimentally.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 975388
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 80, Issue 4, 2009; Related Information: Article No. 045327
- Country of Publication:
- United States
- Language:
- English
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