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Self-assembled type-II ZnTe quantum dots (QDs) were grown on GaAs (0 0 1) substrates with Zn 1− x Mg x Se ( x =0.24 and 0.52) buffer layers by molecular beam epitaxy. The optical properties of ZnTe QDs were investigated by low-temperature photoluminescence (PL) and time-resolved PL. An abrupt variation of the PL peak energy with coverage implies the existence of wetting layer of 3.2 MLs and 4.0 MLs for the Mg concentration x =0.24 and 0.52, respectively. The thickness of wetting layer is larger than that of ZnTe QDs grown on ZnSe buffer layers because the strain between ZnTe and Zn 1− x Mg x Se is smaller. The non-mono-exponential decay profiles reflect the processes of carrier transfer and recapture. The Kohlrausch׳s stretching exponential well fits the decay profiles of ZnTe/Zn 1− x Mg x Se QDs. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the growth mode of highly lattice-mismatch () CdTe self-assembled quantum dots grown on a ZnSe buffer-layer by molecular beam epitaxy. Two growth processes were used to prepare the samples. For the group-I samples, Te and Cd sources were alternately used to deposit a CdTe coverage layer of 0.6 to 8.0 mono-layers on a Zn-stabilized ZnSe buffer layer. The growth process of group-II samples was reversed; that is, the Cd beam was supplied first on a Se-stabilized ZnSe buffer layer. The optical spectra, including the power-dependent, time-resolved photoluminescence (PL) and PL excitation measurement, demonstrate a ZnTe-like and a CdSe-like two-dimensional precursor layer (wetting layer) in the group-I and group-II samples, respectively. Following the formation of the precursor layer, three-dimensional highly strained CdTe quantum dots were formed. Accordingly, the growth of CdTe self-assembled quantum-dot structures was attributed to the quasi-Stranski–Krastanow mode. [Copyright &y& Elsevier]

Abstract: The σ + and σ − circularly polarized time-integrated and time-resolved Photoluminescence (PL) measurements were employed to investigate the carrier spin dynamics of ZnMnTe/ZnSe Quantum Dots (QDs) grown on GaAs substrates by molecular beam epitaxy. The Kohlrausch’s stretching exponential function well correlates both the σ + and σ − decay profiles. The measured spin relaxation time is about 23ns. [Copyright &y& Elsevier]

The optical properties of Mg x Zn 1−x O films with x=0.03, 0.06, 0.08, and 0.11 grown by molecular beam epitaxy ( MBE ) have been studied by temperature-dependent photoluminescence (PL) measurement. It is presented that the full-width at half-maximum (FWHM) of the 12 K PL spectrum of MgZnO films increases with increasing Mg concentration and would deviate significantly from the simulation curve of Schubert model with higher Mg contents. The abnormal broader PL FWHM is inferred from larger compositional fluctuation by incorporating higher Mg contents, which results in larger effect of excitonic localization to induce more significant S-shaped behavior of the PL peak energy with temperature dependence. Additionally, the degree of localization increases as the linear proportion of the PL FWHM, indicating that the excitonic behavior in MgZnO films belong to the strong localization effect. [ABSTRACT FROM AUTHOR]

Abstract: The growth and optical properties of self-assembled ZnO nanorods grown on Si(111) substrate by plasma-assisted molecular beam epitaxy (PA-MBE) were studied. By controlling the Zn/O flux ratio, the growth of ZnO nanorods on Si(111) substrate without catalyst has been achieved. Scanning electron microscopy (SEM) shows the ZnO nanorods with various density and diameter could be controlled. Photoluminescence (PL) measurements exhibit nice optical properties. The sharp near band edge PL emission with full width at half maximum (FWHM) of about 17meV indicates that the ZnO nanorods could be used as the high efficient photonic devices. [Copyright &y& Elsevier]

Abstract: The thermal-activated carrier transfer processes in a Zn0.98Cd0.02O thin film grown by plasma-assisted molecular beam epitaxy were investigated using temperature-dependent and time-resolved photoluminescence (PL) spectroscopy. As the temperature increases from 50 to 220K, the carriers transfer from shallow to deep localized states. Additionally, the carriers escape from the deep localized states above 220K due to an activation energy of about 19meV. [Copyright &y& Elsevier]

Abstract: Zn1−x Mn x O (x=0–0.061) thin films were grown by molecular beam epitaxy (MBE) system. Transmittance shows an increase of the band gap with the increasing Mn concentration. Resonant Raman scattering (RRS) spectra showed 11 longitudinal optical phonon lines for the Zn1−x Mn x O samples. For the Zn0.997Mn0.003O sample, circular polarization degree of 9% was observed at magnetic field B=5T. The dependence of circular polarization rate on the magnetic field intensity exhibits Brillouin type para-magnetism. [Copyright &y& Elsevier]

Abstract: We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe1−x O x (x=0−0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe1−x O x decreases with the increase in O concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent β. [Copyright &y& Elsevier]

Abstract: This work investigated the influence of Zn/O flux ratio and Mn-doped ZnO buffer layer on the epitaxial growth of ZnO grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Atomic force microscopy (AFM), photoluminescence (PL) and X-ray diffraction (XRD) measurements indicated that a small amount residual strain of ZnO epilayers was further relaxed under stoichiometric growth conditions due to the better surface migration of the adatoms. Moreover, we observed that a small amount of Mn doping led to obtain a flatter surface with stronger lattice relaxation maybe due to the greatly enhanced surface migration of the adatoms. By adding a Mn-doped ZnO buffer layer the optical and electrical properties of the ZnO epilayers had significant improvement. [Copyright &y& Elsevier]

Abstract: Self-assembled CdSe/ZnSe quantum dots (QDs) were grown at various growth temperatures on GaAs (001) by molecular beam epitaxy. An optimum growth temperature for CdSe/ZnSe QDs was found to be 260°C. The Stranski–Krastanow (SK) growth mode was confirmed clearly by atomic force microscopy images. The coherent SK QDs were observed from 2.5 monolayers (MLs). Two types of QDs were found with the CdSe coverage of 3.0MLs. It was attributed to a growth mode change from the coherent SK growth mode to the ripening growth mode. A schematic diagram of the growth mechanism of self-assembled CdSe QDs was presented. Moreover, the photoluminescence spectra of samples with various thicknesses were investigated. A dramatic change of optical properties confirmed that the QD structure formed with thickness above 2.5MLs. Finally, the dot size and the density distributions were controlled after growth by in-chamber thermal annealing. For the sample grown at 3.0MLs, the distribution of dot sizes was controlled from 6.0 to at an annealing temperature of 400°C. [Copyright &y& Elsevier]