Density and temperature dependence of carrier dynamics in self-organized InGaAs quantum dots

Abstract

We have used two-and three-pulse femtosecond differential transmission spectroscopy to study the dependence of quantum dot carrier dynamics on temperature. At low temperatures and densities, the rates for relaxation between the quantum dot confined states and for capture from the barrier region into the various dot levels could be directly determined. For electron-hole pairs generated directly in the quantum dot excited state, relaxation is dominated by electron-hole scattering, and occurs on a 5 ps time scale. Capture times from the barrier into the quantum dot are of the order of 2 ps (into the excited state) and 10 ps (into the ground state). The phonon bottleneck was clearly observed in low-density capture experiments, and the conditions for its observation (namely, the suppression of electron-hole scattering for nongeminately captured electrons) were determined. As temperature increases beyond about 100 K, the dynamics become dominated by the re-emission of carriers from the lower dot levels, due to the large density of states in the wetting layer and barrier region. Measurements of the gain dynamics show fast (130 fs) gain recovery due to intradot carrier-carrier scattering, and picosecond-scale capture. Direct measurement of the transparency density versus temperature shows the dramatic effect of carrier re-emission for the quantum dots on thermally activated scattering. The carrier dynamics at elevated temperature are thus strongly dominated by the high density of the high energy continuum states relative to the dot confined levels. Deleterious hot carrier effects can be suppressed in quantum dot lasers by resonant tunnelling injection.

DC electric field effects on the electron dynamics in double rectangular quantum dots

“…Significant oscillations to the left of the anticrossing are observed in the curve due to the change of the charge distribution related to the asymmetry of the system. The average value of the E-E decay rates is around half of the E-AP values, which agrees with measurements for low carriers densities and high temperatures [14], as in our case. The order of magnitude is lightly smaller than those for single quantum dots (between 0.5-50 ps) [1].…”

Modeling of gain and phase dynamics in quantum dot amplifiers

“…A value of τ e 0 = 7 ps has been obtained from the ratio of GS and ES threshold currents (Markus et al 2003), also in agreement with other previous experimental results (Sun et al 2005). τ h 0 has been showed to be subpicosecond (Norris et al 2005). Here we have considered a τ h 0 of 250 fs.…”

On inhibiting Auger intraband relaxation in InAs/GaAs quantum dot intermediate band solar cells

“…13) (in very good agreement with other theoretical and experimental results [19][20][21][22], and therefore, it is, in contrast to the cases discussed previously, the mechanism that could jeopardize the E FC À E FI quasi-Fermi level separation and in turn the voltage preservation in the IBSC. If the excitonic gap between e 0 and h 0 (i.e., E H ) has to be preserved to maintain the good IBSC open circuit voltage, an alternative way to mediate the electron cooling rate is to reduce the overlap between the wave functions that enter Eq.…”