Sub-Monolayer Multilayerd Type-II Quantum Dots Grown by Migration Enhanced Epitaxy

Presented by Prof. Igor Kuskovsky, Department of Physics, Queens College of CUNY

Semiconductor heterostructures can be classified according to the band alignment between two adjacent materials. The vast majority of studies involved so-called type-I systems, where the narrower gap material presents a potential well for both electrons and holes. There, however, exist systems (so-called type-II) where the band alignment has a staggered character, i.e. the material with the lower potential energy for electrons have the higher energy for holes and vice versa, so the charge carriers are separated in the real space. We have fabricated such systems, based on Zn-Te-Se multilayers. Specifically, we fabricated sub-monolayer Zn(Mg)Te/ZnSe and ZnTe/Zn(Cd)Se stacked quantum dots (QDs) via migration enhanced epitaxy (MEE). Here, the holes are confined within Zn(M)Te dots, whereas electrons are located in Zn(Cd)Se barriers.
I this talk I will discuss our studies of these systems as well as their potential applications. Specifically, I will show results of cw and time-resolved (TR) photoluminescence (PL) confirming type-II band alignment; then, I will present magneto-PL, which exhibit oscillations in both energy and intensity as a function of the magnetic field (flux), and explain it via the excitonic Aharonov-Bohm (AB) effect. I will further show recent spectral analysis of the AB oscillations, which showed that the systems we study have two distinct set of stacks, and that oscillator strength of the AB excitons behaves differently from those predicted for nanorings. Finally, I will discuss our recent work on doping of such QDs with the goal of using them for intermediate band gap solar cells.