AVS 60th International Symposium and Exhibition
    Surface Science Monday Sessions
       Session SS+AS+NS-MoM

Paper SS+AS+NS-MoM8
Study of the Coupling of Ultra-thin CdSe Double Quantum Wells

Monday, October 28, 2013, 10:40 am, Room 201 A

Session: Nanostructures: Growth & Characterization
Presenter: I. Hernández-Calderón, Cinvestav, Mexico
Authors: J.A. Lorenzo-Andrade, Cinvestav, Mexico
F. Sutara, Cinvestav, Mexico
I. Hernández-Calderón, Cinvestav, Mexico
Correspondent: Click to Email
The degree of coupling between adjacent quantum wells (QW) will depend on the sample structure and electronic properties of the QW and barrier materials. The design of heterostructures containing multiple QWs requires the precise knowledge of the minimum barrier thickness to couple/uncouple the neighboring QWs. In this work we present the results obtained from calculations employing the matrix transfer method (MTM) and the analysis of the excitonic spectra of heterostructures containing two CdSe ultra-thin quantum wells (UTQWs). The thickness of each quantum well, in the range from 1 to 3 monolayers (ML), was identical (symmetrical structure) or different (asymmetrical structure). The UTQWs were grown by atomic layer epitaxy (ALE) within ZnSe barriers onto GaAs(001) substrates. Due to the finite confinement the wave function of electron and holes will penetrate the ZnSe barriers, the degree of coupling of the CdSe QUTWs will depend on the thickness of the separating barrier. Then, a practical approach to determine the thickness to uncouple the pair of symmetrical QWs is the analysis of the evolution of the energy levels of the QWs as a function of the separating barrier thickness: as soon as the energy levels present a negligible change (and then identical values), we have uncoupled the QWs. We observed that, the thinnest the quantum well the largest the penetration of the electron and hole wave functions into the ZnSe barrier. From the MTM calculations barriers in the range from 12 to 26 ML are necessary to uncouple symmetrical UTQWs with thickness in the range from 5 to 1 ML. These results are also useful to explain the behavior of the FWHM of the UTQWs as a function of their thickness. A similar approach was employed for the case of asymmetrical UTQWs. The coupling/uncoupling of asymmetrical structures was experimentally verified by the analysis of the excitonic spectra at low and room temperature: in the case of coupling only the lowest energy transition is observed; for the case of uncoupled UTQWs the photoluminescence spectrum presents two peaks, one for each independent UTQW.

*Partially supported by Conacyt-Mexico.