Surface InP Quantum Dots: Effect of Morphology on the Photoluminescence Sensitivity

Abstract An investigation of the photoluminescence sensitivity of epitaxial surface InP quantum dots grown on In 0.48 Ga 0.52 P buffer layer lattice matched to GaAs substrate is presented. The emission wavelength of such quantum dots can be defined through the quantum dot dimensions in the range 750 – 865 nm. Quantum dot exposure to polar solvent vapour (methanol and ethanol) determines in any investigated case a luminescence intensity enhancement. The response to alcohol vapours affects only the luminescence intensity while peak position and shape remain unchanged. Optimization of the sensor response by tailoring quantum dots size and coverage has been demonstrated

Ferromagnetism induced in diluted A₁₋xMnxB semiconductors

Theoretical model has been developed for analysis of the peculiarities of new type of magnetism in diluted magnetic A₁₋xMnxB semiconductors. The coherent potential is introduced using the dynamic mean field theory (DMFT) approximation and the Baym- Kadanoff hypothesis valid for the case x < xc (xc is the percolation limit)

Optical characterization of pseudomorphic AlGaAs/InGaAs/GaAs heterostructures

Pseudomorphic strained-layer AlxGa₁₋xAs/InyGa₁₋yAs/GaAs heterostructures have been studied by means of photoluminescence and Raman scattering. It is established the correlation between the photoluminescence line shape changes and the Raman spectra modification when the quantum well width is below the critical layer thickness estimated to be of 25 nm for y = 0.1. The photoluminescence feature observed for the InGaAs quantum well width equal to 20 nm as extremely narrow exciton-like peak with the full width at half of maximum equal to 1.5 meV at low temperature (T = 6 K) transforms into broad band of the full width at half of maximum equal to 16 meV when the quantum well width reaches the value about of 12 nm. The photoluminescence line shape broadening is accompanied by the modifications of Raman spectra. A new line arising at the spectral position ν = 160 cm⁻¹ is assigned to impurity-induced longitudinal acoustic mode of InyGa₁₋yAs. The changes observed in optical spectra are related to the generation of defects in the under-critical layer thickness region

Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Xt – Xl valley crossover and deformation potential in AlP/GaP quantum wells

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Excitation correlation photoluminescence in the presence of Shockley Read Hall recombination

Excitation correlation photoluminescence ECPL measurements are often analyzed in the approximation of a cross correlation of charge carrier populations generated by the two delayed pulses. In semiconductors, this approach is valid for a linear non radiative recombination path, but not for a non linear recombination rate as in the general Shockley Read Hall recombination scenario. Here, the evolution of the ECPL signal was studied for deep trap recombination following Shockley Read Hall statistics. Analytic solutions can be obtained for a fast minority trapping regime and steady state recombination. For the steady state case, our results show that the quadratic radiative term plays only a minor role, and that the shape of the measured signal is mostly determined by the non linearity of the recombination itself. We find that measurements with unbalanced intense pump and probe pulses can directly provide information about the dominant non radiative recombination mechanism. The signal traces follow the charge carrier concentrations, despite the complex origins of the signal, thus showing that ECPL can be applied to study charge carrier dynamics in semiconductors without requiring elaborate calculations. The model is compared with measurements on a reference sample with alternating layers of InGaAs InAlAs that were additionally cross checked with time resolved optical pump terahertz probe measurements and found to be in excellent agreemen

Xt – Xl valley crossover and deformation potential in AlP/GaP quantum wells

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Diluted magnetic А₁₋xMnxВ semiconductors

Novel model of the diluted magnetic semiconductors (DMS) А₁₋xMnxВ possessing the metallic conductivity is proposed. Using the coherent potential technique the electron scattering by the randomly distributed Mn centers is taken into account. The exchange scattering of the electron spin by the localized magnetic mo exactly basing on the spin-polaron limit for the Vonsovskii Hamiltonian