Ellipsometric study of InAs wetting layer in InAs/GaAs quantum dots at the threshold of quantum dot formation

Abstract

Using room temperature spectroscopic ellipsometry, we measured the pseudo-dielectric function of self-assembled InAs/GaAs quantum dots at the onset of quantum-dot nucleation in the spectral range from 0.8 to 6 eV. The nominal In coverage varied from 1 to 2.6 ML. In addition to the quantum-dot-related feature at 1.1 eV, we observed two high energy transitions near 1.34 and 1.38 eV which arose from the InAs wetting layer. These two high energy features merged in 1-ML-thick wetting layer. We fitted the dielectric function of InAs wetting layer in the visible range performing multilayer analysis, and found strong excitonic enhancement and blue shift of the E1 peak.

Wetting layer states of InAs∕GaAs self-assembled quantum dot structures: Effect of intermixing and capping layer

“…This, however, seems to remain in contradiction to some experimental observations regarding energies of the optical transitions reported by different authors, concerning, for instance, the InAs/ GaAs WL QWs. [9][10][11][12][13][14][15][16] They are very similar in many reports and are usually in satisfactory agreea͒ Author to whom correspondence should be addressed; electronic mail: grzegorz.sek@pwr.wroc.pl ment with the calculations assuming a rectangular well shape and its fractional thickness of about 1.5 monolayer. [17][18][19] In this paper we aim at presenting a more detailed discussion of the optical transitions related to the existence of the wetting layer in the InAs/ GaAs QD structures, for which we use as main experimental tools the transmission electron microscopy ͑TEM͒ to deduce the composition profiles and photoreflectance spectroscopy to study the absorptionlike spectra.…”

“…It explains both the independence of the WL QW transition energies of the growth conditions in the two InAs layers of our structure ͑the one without the InGaAs cap͒ and their almost constant values over a very broad range of different InAs/ GaAs QD structures reported in the literature. [9][10][11][12][13][14][15][16] In Fig. 6, we have summarized how the room temperature data are scattered in the published papers.…”

“…6, we have summarized how the room temperature data are scattered in the published papers. [9][10][11][12][13][14][15][16] It shows indeed that in spite of different growth conditions used in different laboratories, which influence the dot properties ͑e.g., the data concerning the QD ground state transition energy differ significantly in these reports͒, the WL transition energy remains almost constant within a very narrow range. It might be fully explained, thanks to the calculations we made assuming the QW interface intermixing ͑see Fig.…”

Ripening of InAs quantum dots on GaAs (001) investigated with in situ scanning tunneling microscopy in metal–organic vapor phase epitaxy

“…single photon emitter [1,2], has also increased the need for a better understanding of the growth and modification of quantum dots (QDs). Especially for metal-organic vapor phase epitaxy (MOVPE)-the most important growth method for mass fabrication of III-V semiconductor devices-improving the QD device performance has mostly been limited to empirical trial and error processes.…”