Blue Shift Of Photoluminescence Band Research Articles

Submicron Raman and photoluminescence topography of InAs/Al(Ga)As quantum dots structures

Two-period structures with and without vertical coupling between indirect and direct bandgap InAs quantum dots (QDs) both with type I band alignment, grown by molecular-beam epitaxy, were investigated by confocal Raman and photoluminescence (PL) microspectroscopy. The observed blue shift of PL band of the indirect (direct) bandgap QD by 20 (80)meV with decrease of thickness of Ga(Al)As intermediate layer between two InAs QD layers from 30 to 8nm is considered as caused by increase of elastic strains (decrease of QDs sizes) in QD layers and by coupling between QDs electronic states. Scanning confocal resonant Raman microspectroscopy was applied for non-destructive evaluation of composition at various depths along the thickness of vertical coupling of the upper InAs/AlGaAs and lower InAs/AlAs QDs layers of the sandwich structures. Based on the analysis of determined from the in-depth Raman spectra optical phonons frequencies, the depth distribution of composition in InAlAs and GaAlAs alloy layers formed as a result of strain-driven enhanced interdiffusion was determined.

Piezoelectric effects in InAs/GaAs(N11) self-assembled quantum dots

The effects of a piezoelectric field on the spectroscopic properties of strained InAs/GaAs self-assembled quantum dot (QD) heterostructures grown on (N11) substrates with A or B termination are presented. An increasing blue shift of photoluminescence (PL) band was observed with increasing excitation density. The PL blue shift of (N11) quantum dots measured at the highest excitation grows with 1/N and shows an asymmetric dependence on whether the substrate has A or B termination. We attributed the blue shift of the photoluminescence band to the screening of the piezoelectric field by the photo-generated carriers, leading to a reduction of the piezoelectric induced quantum confined Stark effect.

Spectroscopic studies of the interaction of C 60 and C 70 films with metal substrates

The interaction of fullerenes C 60 and C 70 films with metal substrates Au, Ag, In and Sn has been studied by UV-visible absorption spectra, IR, Raman, photoluminescence and second-order nonlinear optics. The absorption spectra show new bands for films on Au, Ag, In and Sn film substrates. For C 60 on Au and Ag, new bands appear, peaking at 723 and 566 nm, respectively. For C 60 film on Sn, several new bands are found at 975.4, 1218, 1557, 2000 and 3570 nm in the NIR and IR regions. Raman spectra reveal an additional peak at 350 cm−1 for C 60 film on Au and five new peaks at 350, 532, 564, 1692 and 1850 cm−1 for the film on Sn. An enhancement of the Raman peak intensity is observed in the latter case. A peak blue shift of photoluminescence band from 749 to 735 nm for C 60 on Sn has also been found. Moreover, a second-order nonlinear optics study at 1.06,μm yields a ten times greater secondary harmonic generation signal intensity for C 60 films on Ag than that of Ag, while no signal is observed for C 60 film on glass. For C 70 on Sn, UV absorption bands broaden and new bands are found at 747, 984 and 1738 nm. The above results suggest a structural distortion of C 60 and C 70 molecules, induced by charge transfer from these metals to the molecules.