Efficient, narrow linewidth excitonic emission at room temperature from GaAs/AlGaAs V-groove quantum wire light-emitting diodesThe effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with "light hole up" configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (pÀAl x Ga 1Àx As= GaAs 1Ày P y =nÀAl x Ga 1Àx As) with y ¼ 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning. V C 2012 American Institute of Physics. [http://dx.
Numerical calculations and experimental results show that, for the broad range of tensile strained p-Al x Ga 1−x As/GaAs 1−y P y /n-Al x Ga 1−x As heterostructures widely used in commercial laser diodes emitting at 766-808 nm, polarization of emitted light may be extremely sensitive to external uniaxial stress due to the change of wave functions symmetry and possible optical transitions in the quantum well levels system. In some heterostructures with quantum well width of 10 nm and phosphorus content below 0.08, TM/TE polarization mode relation showcases a several times decrease and even dominant polarization mode switching under moderate compression of about 5-6 kbar in [100] and [110] directions.
Using the group method, single crystals of NdSc 3 (BO 3 ) 4 are grown from a melt solution and X-ray structural studies are performed. It is shown that at room temperature the NdSc 3 (BO 3 ) 4 crystal has a huntite-type structure with space group P3 1 21. The temperature dependence of the heat capacity shows anomalous behaviour at Т = 504 ± 1 K. This anomaly corresponds to a structural phase transition from R32 to P3 1 21. It is known that a similar transition occurs in RFe 3 (BO 3 ) 4 crystals; an anomaly in the specific heat is also observed. Theoretical calculations are carried out from the first principles of the lattice dynamics of the crystal under study in a high-symmetry phase with the R32 space group. An unstable (soft) mode in the boundary point of Brillouin zone was found. It was determined that this structural instability is responsible for the structural displacement-type phase transition R32 → P3 1 21.
In this study, the conventional and inverse barocaloric effects (BCE) in ferroelectric NH4HSO4 are reported. Maximum extensive and intensive BCE near order-disorder phase transition can be achieved at low pressure p ≤ 0.1 GPa. Large thermal expansion of the crystal lattice plays a very important role in the developing conventional BCE and conversation between BCE of different sign in the narrow temperature range. 1 Dear Editor, Consider please our manuscript, devoted to some new results obtained during the study of the intensive and extensive barocaloric effects near phase transitions in ferroelectric NH 4 HSO 4. We hope that the results will be of interest to readers of Journal of Alloys and Compounds.
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