Photoluminescence of ZnBeMnSe solid solutions

In this paper optical properties of Zn1-x-yBexMnySe mixed semiconductors were studied as a function of both, temperature and excitation power. The crystals under investigation were grown by the high-pressure, high-temperature vertical Bridgman technique within the range of the composition 0.05 ≤ x,y ≤ 0.2. Photoluminescence spectra for the lowest content of Mn and Be exhibit character typical for II-VI semiconductors together with intensive yellow-orange manganese emission. Evolution of the excitonic emission as the function of temperature allowed determining the energy gap of the investigated semiconductors. Absorbance and photoluminescence excitation spectra confirmed crystal field splitting of excited atomic terms of manganese ions into the states, denoted according to the crystal field theory in the case of tetrahedral symmetry. Temperature and laser power dependences of luminescence showed anomalous behavior of the manganese emission. It turned out that the position of the Mn2+ related luminescence band does not change monotonically with the variation of the temperature or the excitation power. Finally, switching of the manganese emission has been observed. By increasing laser power of exciting radiation, the Mn-related emission could be quenched by almost two orders in magnitude. This effect was especially strong at low temperature and it was fully reversible

On the optimization of experimental parameters in photopyroelectric investigation of thermal diffusivity of solids

In this paper, the possibility of optimizing the experimental conditions for a correct photopyroelectric evaluation of the thermal diffusivity of solid samples is studied. For this purpose, a glassy carbon sample, with known thermal properties, was selected as test material and two types of techniques were applied in order to get the value of its thermal diffusivity: (i) the photopyroelectric calorimetry in back detection configuration and (ii) the infrared thermography. Assuming that the values of thermal diffusivity obtained by thermography are correct (a non-contact technique), we studied how to eliminate the underestimation (due to the presence of the coupling fluid) of the results in the back photopyroelectric calorimetry investigations. Experiments with different types of coupling fluids and numerical simulations were performed in order to evaluate the influence of the coupling fluid on the value of the thermal diffusivity. The conclusion is that a proper choice of the type of coupling fluid and some improvements performed in the experimental design of the photopyroelectric calorimetry detection cell (with the purpose of reducing the coupling fluid’s thickness), can eliminate the difference between the results obtained with the two photothermal (contact and non-contact) techniques

Near-forward Raman study of a phonon-polariton reinforcement regime in the Zn(Se,S) alloy

We investigate by near-forward Raman scattering a presumed reinforcement of the (A-C,B-C)-mixed phonon-polariton of a A1-xBxC zincblende alloy when entering its longitudinal optical (LO-)regime near the Brillouin zone centre {\Gamma}, as predicted within the formalism of the linear dielectric response. A choice system to address such issue is ZnSe0.68S0.32 due to the moderate dispersion of its refractive index in the visible range, a sine qua non condition to bring the phonon-polariton insight near {\Gamma}. The LO-regime is actually accessed by using the 633.0 nm laser excitation, testified by the strong emergence of the (Zn-Se,Zn-S)-mixed phonon-polariton at ultimately small scattering angles

High pressure x-ray diffraction and extended x-ray absorption fine structure studies on ternary alloy Zn1−xBexSe

International audienceThe ternary semiconductor alloy Zn1−xBexSe has been studied under high pressure by x-ray diffraction and extended x-ray absorption fine structure EXAFS at the Zn and Se K-edge in order to determine the bulk and bond-specific elastic properties. Our measurements on samples with x =0.06–0.55 show pressure induced phase transformation from zinc blende to NaCl. The phase transformation pressure increases linearly with x. Murnaghan equation of state fitting to the data yields the unit cell volume at ambient pressure and bulk modulus, both of which follow the Vegard's law. Nearest neighbor bond distances derived from EXAFS do not show sharp phase transition except for x=0.06. Bond modulus derived for the Zn–Se bonds shows them to be apparently stiffer than the bulk alloy, which is nontrivial. This tendency increases with increasing x and a strong positive bowing from the Vegard's law is observed. We attribute the observed anomalies to the contrastingly different properties of the two components ZnSe and BeSe

The Phonon Percolation Scheme for Alloys: Extension to the Entire Lattice Dynamics and Pressure Dependence

International audienceWe explore two basic issues behind the 1-bond ! 2-mode percolation scheme that has recently lead to a unification of the classification of the Raman and infrared spectra of usual zincblende semiconductor alloys. In doing so we focus on the model ZnBeSe alloy, for which the percolation scheme was originally developed. First, we show by using inelastic neutron scattering that the well-resolved 1-bond ! 2-mode percolation doublet of the short Be-Se bond detected close to the zone center by Raman and infrared spectra remains observable throughout the whole Brillouin zone up to the zone edge. This testifies for an origin at the bond scale. Second, high-pressure is used to disable a Fano interference which screens the Zn-Se Raman signal, revealing a distinct Zn-Se percolation doublet. This provides experimental evidence that the 1-bond ! 2-mode percolation scheme is generic, and may, in principle, apply to all bonds in an alloy