Carrier capture dynamics of single InGaAs/GaAs quantum-dot layers

Abstract

Using 800 nm, 25-fs pulses from a mode locked Ti:Al 2 O 3 laser, we have measured the ultrafast optical reflectivity of MBE-grown, single-layer In 0.4 Ga 0.6 As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and annealing temperature. With increasing excited carrier density, the capture rate decreases; this slowing of the dynamics is attributed to Pauli state blocking within the InGaAs quantum layer.

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“…This increase is likely due to highly energetic free carriers, which are captured in the CIGS energy states and relax quickly into the lowest energy state. The capture of free carriers can occur via carrier-phonon or carrier-carrier interactions with a typical capture time of 0.6-4.5 ps, depending on the incident fluence [38].…”

Effect of phonon confinement on one- and two-polar optical phonon capture processes in quantum dots

“…This is explained by the fact that for the two-phonon capture case the capture rate is less and, naturally, the saturation of the population in a quantum dot due to the Pauli exclusion principle must be realized for the relatively higher concentrations of electrons in the barrier region. The experiments [9], carried out at relatively high excitation levels, also reveal the impact that state blocking has upon carrier capture dynamics in single InGaAs/GaAs QD layers.…”

“…The understanding of ultrafast carrier dynamics in QDs is important for operation of optoelectronic devices such as QD lasers [1], QD infrared photodetectors [2], and QD optical amplifiers [3]. Time-resolved photoluminescence spectroscopy with picosecond [4][5][6] and subpicosecond resolution [7] as well as subpicosecond optical pump-probe experiments [8,9] have been applied to obtain an information on carrier dynamics in various QD systems. In a typical experiment, carriers in the surrounding QD barrier layers are initially excited.…”

Interdot carrier and spin dynamics in a two-dimensional high-density quantum-dot array of InGaAs with quantum dots embedded as local potential minima

“…In general, the increase of the QD density is required for achieving a higher luminance and optical gain [7] while developing QD-based spin-functional optical devices, such as spin-polarized lightemitting diodes [8][9][10] or laser diodes [11]. For the spin-related properties, high-density QDs have a significant potential of higher spin-polarized emission owing to their faster capture of electron spins from a three-dimensional semiconductor barrier while maintaining high spin polarization [12]. However, there remains a lack of understanding of the carrier and spin dynamics in high-density QD ensembles due to the emissions from these ensemble states including various contributions, such as differently-sized QD states and the influence of interdot coupling between the carrier wavefunctions of neighboring QDs.…”