Ultrafast photocarrier relaxation processes in Er-doped InAs quantum dots embedded in strain-relaxed InGaAs barriers

Time-resolved transmission change of Er-doped InAs quantum dots (QDs) embedded in strain-relaxed In0.45Ga0.55As barriers has been studied using different excitation wavelengths (1.4-1.55 mu m) to understand the QD-size dependence of the photocarrier relaxation. Each measured temporal profile was well reproduced by a sum of three exponential decays. Ultrafast (similar to 1.6 ps) and fast (similar to 6-9 ps) components are dominant in the initial stage of decay, and then the slow (similar to 70-130 ps) component due to the radiative recombination in the QDs appears to be seen. The first two components come from photocarrier relaxation into the nonradiative centers related to Er dopants or the lattice relaxation. The difference is considered to result from whether the nonradiative centers are positioned inside or outside the QDs. The decay time for the outside case becomes shorter as the excitation wavelength is shortened, which might be due to the weaker confinement of photocarriers in the smaller-size QDs. Suppression of the QDs contributing to the radiative recombination is also more significant for the smaller-size QD excitation. (c) 2012 Elsevier B.V. All rights reserved.