Abstract
We studied the temperature-dependent photoluminescence (PL) and time-resolved PL spectra of multilayer CdTe/ZnTe quantum dots (QDs) to understand their carrier dynamics. We demonstrated a method of enhancing the confinement of carriers in CdTe QDs by modulating the number of stacked layers, leading to enhanced acoustic phonons up to 67 μeV and reducing the optical phonon coupling to 20 meV with an average phonon energy of 20 meV. The temperature-dependent decay time could be explained using a simple model of the thermal redistribution of carrier states. Thermal escape from hole states during multiphonon scattering occurred only at high temperatures, whereas blue shifts and enhanced PL intensity were expected to enhance the electron–phonon coupling and confinement-induced mixing among discrete state and continuum states with separation energies of 3.5–7.4 meV. Time-resolved PL measurements probed the electric field screening effect as a function of the strain distribution in QDs and was established to be 2.5 ± 0.2 MV/cm.
Highlights
Semiconductor quantum dots (QDs) that display a large nonlinear optical response, ultrafast signal switching, quantum efficiency, and high-temperature stability are important for use in future photonic devices, optical data storage, and optical computing[1,2,3,4]
Transitions between intrinsic and surface states[27], an increase in the electron–hole pairs due to surface-trapped carriers[28,29] and the thicknesses of the ZnTe separation layers do not affect the quantum barrier resulting from the growth of defects in CdTe QDs with a large number of layers
The separation energy ΔE corresponds to the energy of a confined acoustic phonon in QDs30–32
Summary
Semiconductor quantum dots (QDs) that display a large nonlinear optical response, ultrafast signal switching, quantum efficiency, and high-temperature stability are important for use in future photonic devices, optical data storage, and optical computing[1,2,3,4]. Self-assembled QDs form as a consequence of layer-to-layer strain relaxation, which often results in non-uniform particles and difficulties controlling dot size and density[8,9,10] These synthetic difficulties highlight important issues around controlling the size, density, and uniformity of the particles because the optical properties of QD-based photonic devices depend on the size, density, and uniformity of QDs. Control over the growth parameters, reorganization of a surface into islands through post-growth thermal annealing, the presence of a capping layer, and the effects of different substrates can successfully manipulate the size, density, and uniformity of QDs11–13. Nonradiative processes affect carrier relaxation via thermal escape involving hole states, the energy separation among the fine-structured states was expected to differ in the stacked layers for a number of reasons: (a) electron–phonon coupling was enhanced; (b) confinement-induced www.nature.com/scientificreports/. Mixing occurred between discrete states and continuum states due to the intermixing among layers of the QDs and separation layers
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