Quantum islands formation and optical properties of CdZnTe/ZnTe quantum wells grown by atomic layer epitaxy

Abstract

PACS 78.55.Et, 78.67.De, 81.15.Hi In this work we report on optical properties of CdZnTe/ZnTe quantum wells (QWs) grown by atomic layer epitaxy (ALE) and the formation of quantum island during the QWs growth. The photoluminescence (PL) emission of QWs at lower temperature (250 °C) consists of two peaks. From studying the dependence of the PL integrated emission with the excitation intensity, it is found that theses both PL features have different nature. The high-energy sharp peak is associated to the excitonic recombination in the CdZnTe/ZnTe alloy quantum well while the low-energy contributions (wide peak) are assigned to the recombination in the quantum islands (compositional fluctuations with high Cd molar fraction embedded inside the active zone of the QW). The temperature dependence of the PL FWHM, energy, and intensity confirm the enhancement of the quantum efficiency of optical recombination in quantum islands. The formation of quantum islands is more likely at lower growth temperature as evidenced by the optical properties of the QWs grown at different temperatures. Since the QWs growth is following an ALE procedure (Cd -Te -Zn -Te cycles), the existence of a Cd desorption induced by Zn exposure (Cd atoms are replaced by Zn atoms) leads to the formation of the compositional fluctuations (islands) on the growing surface at lower temperatures.

Modification of the photoluminescence characteristics of CdZnTe/ZnTe QWs by CdTe monolayer film insertion

“…A two-component shape of the QW PL band has also been observed in CdTe/ZnTe QW structures grown by MBE at high (350 −480 °C) temperatures or with applying long time healing after CdTe deposition [10], in CdTe/ZnTe quantum dot structures [11,12], in CdTe/CdZnTe QW structures or in Cd 1-x Zn x Te/ZnTe QWs grown by atomic layer epitaxy (ALE) at low temperatures (250−275 °C) [13]. In all these cases, formation of Cd-enriched nanoislands (quantum dots) inside the QW was supposed.…”