Quantum Dot Clusters Research Articles

Cathodoluminescence wavelength imaging of μm-scale energy variations in InAs/GaAs self-assembled quantum dots

Cathodoluminescence wavelength imaging of InAs/GaAs self-assembled quantum dots (SAQDs) was performed to study the spatial variation in the spectral line shape of the broadened quantum dot (QD) ensemble. The line shape was found to vary on a scale of ∼μm, revealing attendant variations in the size distribution of SAQD clusters on this spatial scale. Energy variations in clusters of SAQDs are found to exhibit a spatial correlation with the efficiency of luminescence and the activation energy for thermal re-emission of carriers. A reduction in the energy variation of the QD clusters occurs when the thickness of the spacer layers in vertically self-organized samples is reduced or the number of stacks is increased.

Cathodoluminescence Wavelength Imaging Study of Clustering in InAs/GaAs Self-Assembled Quantum Dots

ABSTRACTCathodoluminescence wavelength imaging (CLWI) of InAs/GaAs self-assembled quantum dots (SAQDs) was performed to study the spatial variation in the spectral lineshape of the broadened quantum dot (QD) ensemble. The lineshape was found to vary on a scale of ∼μm, revealing attendant variations in the size distribution of SAQD clusters on this spatial scale. Energy variations in clusters of SAQDs are found to exhibit a spatial correlation with the efficiency of luminescence and the activation energy for thermal re-emission of carriers. A reduction in the energy variation of the QD clusters occurs when the thickness of the spacer layers in vertically self-organized samples is reduced or the number of stacks is increased. SAQDs were also prepared by punctuated island growth (PIG), in which deposition of the total desired amount is broken into two or more stages each separated by time delays. CLWI reveals a reduced variation in the energy of the dominant CL emission on a ∼μm spatial scale, correlating with a narrower size distribution of larger QDs for PIG, as measured in atomic force microscopy.

Luminescent studies of alloy Zn xCd 1− xSe quantum dots grown on ZnSe by metalorganic chemical vapor-phase deposition

Zn x Cd 1− x Se alloy quantum dots (QDs) with x in the range 0–0.39 are grown by metalorganic chemical vapor-phase deposition on ZnSe. Cathodoluminescence (CL) and photoluminescence (PL) were used to study these self-assembled quantum dots. CL imaging and spectra show that clusters of QDs are efficient luminescent sites. A large red shift of the low-temperature PL peak energy of QDs, despite an increase in Zn, is attributed to a considerable increase in their size. This increase in size is consistent with the results of recent theoretical models. In forming the self-assembled QDs, mismatch strain is regarded as the fundamental driving force. When the strain changes, through a change in the composition of Zn x Cd 1− x Se, QDs of a different size are obtained. A decrease in size, in turn, results in stronger quantum confinement effects. The size of the QDs is very sensitive to small changes of strain. Even a minute reduction in the zinc content of the QDs, achieved through a lengthening of growth interruptions, produces an observable blue shift of luminescence, as a result of the strengthening of the quantum confinement energy.

Self-Assembly of Quantum-Dot Molecules: Heterogeneous Nucleation of SiGe Islands on Si(100)

We report on the formation of clusters of self-assembled quantum dots (termed quantum-dot molecules). Each cluster, typically consisting of four closely spaced SiGe islands, is formed by preferential nucleation around the edges of square pits. Uniform-sized pits are directly formed by controlled deposition of Si and C on the initial Si(100) surface, followed by the growth of a thin Si buffer layer. Formation of ${105}$ pit walls as precursors to island formation and elastic relaxation effects near the pits appear to influence island nucleation. Quantum-dot molecules may have potential applications in nanoelectronic devices and may exhibit novel electronic and optical properties.

Impact excitation of the f–f emission in clusters Er–O in silicon

The Er2O3 quantum dot (cluster) with dimensions about 1.2 nm in silicon is discussed as a possible source of the Er-related emission in Si:Er, O, excited by hot carriers in the light-emitting diodes under reverse bias. This quantum dot is represented as a spherical quantum well 1 eV in depth. The electron resonance level with energy about 0.8 eV above the bottom of the silicon conduction band plays the role of an electron trap. The energy of 1.6 eV hot electrons trapped by the Er–O cluster is transferred to excitation of the f shell of erbium.

The properties of low-threshold heterolasers with clusters of quantum dots

The properties of low-threshold heterolasers with clusters of quantum dots

The Possible Mechanism of Excitation of the f - f Emission from Er-O Clusters in Silicon

AbstractThe Er2O3 quantum dot (cluster) with dimensions about 1.2nm in silicon is discussed as the possible source of the Er related emission in Si:Er,O, excited by photogenerated carriers or in a light-emitting diodes (LED) at forward bias. This quantum dot is represented as a spherical quantum well 0.9eV in depth. The electron level with energy about 0.15eV below the bottom of the silicon conduction band plays role of an electron trap. The trapped electron interacts with a hole in valence band of silicon forming “indirect” exciton bonded to quantum well. The energy is transferred to f - shell of erbium by the Auger electron - hole recombination.

Slow conductance oscillations in nanoscale silicon clusters of quantum dots

At fixed reverse bias voltages of a diode structure consisting of nanoscale silicon particles embedded in an amorphous SiO2 matrix, conductance oscillation in time is observed on some samples at room temperature. Possible mechanisms of the conductance oscillations include the exchange of electrons between the quantum confined states coupled to localized defects and the charge state of these defects. The precise origin of the observed oscillations has not been identified.

Quantum-dot size-distribution analysis and precipitation stages in semiconductor doped glasses

The sequence of stages during precipitation of semiconductor (e.g., CdS, CdSe) clusters from supersaturated glasses exhibiting quantum-confinement effects was investigated. The rate of formation of nanometer-size ‘‘quantum dots’’ distributed in a continuous glass matrix is critically determined by the time and temperature of the heat treatment given to the quenched glasses. The entire precipitation process was analyzed in terms of several decomposition stages: nucleation, normal growth, coalescence of quantum dots, and devitrification of the glass matrix itself. Experimental data obtained by differential thermal analysis were utilized to identify the heat-treatment temperature range associated with the precipitation stages. The size distribution of CdSe quantum-dot clusters was analyzed using our transmission electron microscopy data. The data of Ekimov et al. [Solid State Commun. 56, 921 (1975)] was reduced to time-temperature master plots useful for precipitating quantum dots of a given size in glasses.