E. Velázquez Lozada

Photoluminescence variation in dot-in-a-well structures with different InAs quantum dot densities

Photoluminescence (PL) and its temperature dependence have been investigated in InAs quantum dots (QDs) embedded in In0.15Ga0.85As∕GaAs quantum wells (QWs). The QD density varied from 1.1×1011 down to 1.3×1010cm−2 with an increase in QD growth temperature. Three stages have been revealed in the thermal decay of the PL intensity in InAs QDs. A variety of activation energies of PL thermal decay are discussed. Numerical simulations of experimental PL thermal decay curves give possibility to analyze the area of localization of nonradiative defects in InGaAs∕GaAs QW structures with different InAs QD densities.

Some reasons of emission variation in InAs quantum dot-in-a-well structures

Photoluminescence (PL) and X ray diffraction have been studied in InAs quantum dots (QDs) embedded in symmetric In0.15Ga1-0.15As/GaAs quantum wells (dot-in-a-well, DWELL) with QDs grown at different temperatures. The density of QDs decreases from 1.1×1011 down to 1.3×1010 cm-2 with increasing the QD growth temperatures from 470 to 535°C. The QD density decreasing in DWELLs is accompanied by the non monotonous variation of QD parameters. The PL intensity increases and the PL peak shifts to low energy in structures with QDs grown at 490 and 510°C. On the contrary the structures with QDs grown at 525 and 535°C are characterized by lower PL intensities and PL peak positions shifted to higher energy. The method of X-ray diffraction has been applied with the aim to study the variation of elastic strain in DWELL structures with QDs grown at different temperatures. It was shown that the minimum of elastic strain corresponds to DWELL with QDs grown at 490-525 °C. For lower (470 °C) and higher (535 °C) QD growth temperatures the level of compressive strain increased in DWELLs. The reasons of strain variation are discussed as well.

Photoluminescence Emission and Structure Diversity in ZnO:Ag Nanorods

The photoluminescence, its temperature dependences, as well as structural characteristics by methods of Scanning electronic microscopy (SEM) have been studied in ZnO:Ag nanorods prepared by the ultrasonic spray pyrolysis (USP). The PL spectra of the ZnO:Ag NRs over the temperature range from 10 K to 300 K are investigated. Three types of PL bands have been revealed: i) the near-band-edge (NBE) emissions, ii) defect related emission and iii) IR emissions. It is shown the IR emission corresponds to the second-order diffraction of the near-band-edge (NBE) emission bands. The study of NBE PL temperature dependences reveals that the acceptor bound exciton (ABE) and its second-order diffraction peak disappeared at the temperature higher than 200 K. The attenuation of the ABE peak intensity is ascribed to the thermal dissociation of ABE with appearing of a free exciton (FE). The PL bands, related to the LO phonon replica of FE and its second-order diffraction, dominate in the PL spectra at room temperature that testify on the high quality of the ZnO:Ag films prepared by the USP technology.

Emission and Structure Varieties in ZnO:Ag Nanorods Obtained by Ultrasonic Spray Pyrolysis

Scanning electronic microscopy (SEM), X ray diffraction (XRD) and photoluminescence (PL) have been applied to the study of the structural and optical properties of ZnO nanocrystals prepared by the ultrasonic spray pyrolysis (USP) at different temperatures. The variation of temperatures and times at the growth of ZnO films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnO nanocrystals (NCs), as well as to vary their photoluminescence spectra. The study has revealed three types of PL bands in ZnO NCs: defect related emission, the near-band-edge (NBE) PL, related to the LO phonon replica of free exciton (FE) recombination, and FE second-order diffraction peaks. The PL bands related to the LO phonon replica of FE in PL spectra measured at room temperature testify on the high quality of ZnO films prepared by the USP technology.

Photoluminescence and In/Ga Intermixture in InAs/InGaAs DWELL Structures

The photoluminescence (PL) and photoluminescence temperature dependences have been studied in InAs quantum dots (QDs) embedded in the In 0.15 Ga 1–0.15 As/GaAs quantum wells (QWs) with QDs grown at different temperatures (470–535 °C). Ground state (GS) related QD PL peaks shift into the red side with increasing QD growth temperature to 510 °C and the blue shift is observed when the temperature increased to 535 °C. The temperature dependences of GS PL peak positions were fitted on the base of Varshni relation and the fitting parameters were compared with the bulk InAs and the In 0.21 Ga 0.79 As allow. This comparison has revealed that for QDs grown at 490–510 °C the PL fitting parameters are the same as for the bulk InAs crystal. The DWELL structures with QDs grown at other temperatures have fitting parameters different from the bulk InAs. Last fact testifies that in these structures the Ga/In inter-diffusion between QDs and a QW has been realized. This Ga/In intermixture can be stimulated not only by the high temperature (535 °C), but by the essential elastic stress as well in the DWELL structure with lower QD densities.