A phonon bottleneck is manifested for correlated electron/hole ͑exciton͒ states in self-organized In x Ga 1Ϫx As/GaAs quantum dots ͑QD's͒ with a flat, truncated shape. Suppressed relaxation and hot luminescence from excited states in the low-density regime are demonstrated. The long low-temperature relaxation time of ϳ7.7 ns, being ϳ15 times the radiative lifetime, is attributed to a quenched polar exciton-LO-phonon coupling in truncated QD's based on eight-band k•p model calculations.

Recombination processes in Ga1−xInxNyAs1−y/GaAs multiple quantum wells (MQWs) were investigated as function of the nitrogen molar fraction. We found a pronounced S-shaped behavior for the temperature-dependent shift of the photoluminescence emission similar to the ternary nitrides InGaN and AlGaN. This is explained by exciton localization at potential fluctuations. Time-resolved measurements at 4 K reveal an increase of the decay time with decreasing emission energy. A model based on lateral transfer processes to lower-energy states is proposed to explain this energy dependence. The formation of tail states in the Ga1−xInxNyAs1−y/GaAs MQWs is attributed to nitrogen fluctuations.

Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps.

The exciton-phonon coupling in self-organized InAs/GaAs quantum dots (QDs) is investigated under resonant excitation of the ground-state transition. First- and second-order phonon sidebands of the TO (30.3 meV) and LO (33.2 meV) modes of the strained InAs QDs as well as an interface (35.9 meV) mode are resolved. Huang–Rhys factors of 0.012, 0.026, and 0.006, respectively, indicate enhanced polar exciton-phonon coupling in such strained low-symmetry QDs. Time-resolved measurements support the local character of the phonon modes.

The interaction between point defects in the matrix and excitons localized in self-organized InGaAs/GaAs quantum dots is investigated for structures irradiated by protons. The exciton ground state is demonstrated to be unaffected by radiation doses up to 1014 p/cm2. The close proximity of radiation-induced defects leads to a strong nonmonotonous temperature dependence of the luminescence yield: Carriers are lost via tunneling from excited quantum dot states to irradiation-induced defects below ∼100 K, whereas at higher temperatures, carriers escape to the barrier and are captured by defects.