ABSTRACT
The energy transitions of GaAsSbN/GaAs strained-layer single quantum wells (QWs), grown by molecular-beam epitaxy, are studied in detail, using photoluminescence (PL) and photoreflectance (PR) spectroscopies. The optical transitions energy observed in the PL and PR spectra of GaAsSbN/GaAs QWs show a strong decrease with a small increase in the N composition. These effects are explained through the interaction between the conduction band and a narrow resonant band formed by nitrogen states in the GaAsSbN alloy. The temperature dependence of ground-state energy of strained-layer QWs is analyzed using the Bose-Einstein relation in the temperature range from 9 to 295 K. The parameters that describe the temperature variations of the ground-state energies are evaluated and discussed.
ABSTRACT
Photoluminescence measurements at different temperatures have been performed to investigate the effects of confinement on the electron-phonon interaction in GaAs/AlGaAs quantum wells (QWs). A series of samples with different well widths in the range from 150 up to 750 Å was analyzed. Using a fitting procedure based on the Pässler-p model to describe the temperature dependence of the exciton recombination energy, we determined a fit parameter which is related to the strength of the electron-phonon interaction. On the basis of the behavior of this fit parameter as a function of the well width thickness of the samples investigated, we verified that effects of confinement on the exciton recombination energy are still present in QWs with well widths as large as 450 Å. Our findings also show that the electron-phonon interaction is three times stronger in GaAs bulk material than in Al(0.18)Ga(0.82)As/GaAs QWs.
ABSTRACT
The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.
