Radiative lifetimes of excitons in semiconductor quantum dots

Time-resolved optical characterization of InAs/InGaAs quantum dots emitting at 1.3 μm

“…The lifetime is 1.2 ns independent of temperature for Tр50 K, increases with temperature up to Ϸ2 ns at 150 K, then decreases to 1.8 ns at RT. The constant lifetime value at low temperatures and the subsequent linear increase with temperature has been predicted theoretically 15 and observed before in self-assembled QDs. 16,17 The lateral confinement in the QDs produces nonzero ͑i.e., nonradiative͒ in-plane wave vector k ʈ components in the exciton wave function, thus reducing the radiative emission rate as compared to QWs.…”

“…16,17 The lateral confinement in the QDs produces nonzero ͑i.e., nonradiative͒ in-plane wave vector k ʈ components in the exciton wave function, thus reducing the radiative emission rate as compared to QWs. 15 As the temperature increases, excited states having larger values of k ʈ become populated, and the radiative rate decreases further. The measured low-temperature lifetime of 1.2 ns is much larger than the value calculated by using Citrin's formula, 15 QD (Tϭ0 K)Ϸ370 ps.…”

“…15 As the temperature increases, excited states having larger values of k ʈ become populated, and the radiative rate decreases further. The measured low-temperature lifetime of 1.2 ns is much larger than the value calculated by using Citrin's formula, 15 QD (Tϭ0 K)Ϸ370 ps. This discrepancy may be related to the effect of the specific shape of InAs/InGaAs QDs and of piezoelectric fields on the ground state wave function.…”

Long luminescence lifetime in self-assembled InGaAs/GaAs quantum dots at room temperature

“…[2][3][4][5] The radiative lifetime of strongly confined excitons in QDs, where the energy separation between the ground state and the first excited exciton state is larger than the thermal energy k B T ͑k B is the Boltzmann constant and T is the temperature͒, should be almost independent of T. However, in real QDs, the radiative lifetime of the ground state excitons is expected to increase with increasing temperature due to the thermal population of optically inactive or poorly active exciton states. [6][7][8] This phenomenon was first observed in InGaAs/GaAs QDs by Wang et al 9 in 1994, in InAs/GaAs QDs by Yu et al 10 in 1996, and by other groups later. 11 They found that the photoluminescence ͑PL͒ radiative lifetime increases first with increasing temperature and then decreases at high temperatures.…”

“…[6][7][8] The radiative recombination rate ⌫ R ͑T͒ at temperature T is given by ⌫ R ͑T͒ = ⌫ R ͑0͒ / ͓1+g exp͑−⌬E / k B T͔͒, where ⌬E is the energy difference between the ground state of the QD and some optically inactive excited states and g is the ratio between the degeneracy of the optically inactive states to that of the ground state. The total recombination rate of the QD ground state is given by 11…”