Intraband carrier photoexcitation in quantum dot lasers

Modeling and analysis of distributed feedback quantum dot passively mode-locked lasers

In this paper, we investigate numerically two proposed monolithic distributed feedback quantum dot passively mode-locked lasers (DFB-QDMLLs) with and without gratings in the saturable absorber (SA) section in order to enhance two important performances of QDMLLs for ultrahigh-bit-rate and single-mode applications. We find out that depending on the length of the grating, optical pulses with durations of about 3-8 ps at approximately 2nd and 4th harmonics of cavity round-trip frequencies can be generated by the proposed structures. We also compare the temporal and spectral behaviors of these structures under specified bias conditions and SA lengths. It is shown that DFB-QDMLLs have the ability to generate optical pulses with more peak power than grating-embedded saturable absorber (GESA-DFB-QDMLL) structures which generate shorter pulses with narrower spectral bandwidths. We also show that DFB-QDMLLs operate in a larger range of absorber voltages while the other structure is very sensitive to absorber voltage and operates well for middle ranges of this parameter.

Ultrafast Charge Separation at the CdSe Quantum Dot/Methylviologen Interface: Dependence on Electron Acceptor Concentration

Photoinduced charge transfer dynamics between CdSe semiconductor quantum dots (QDs) and the molecular acceptor methylviologen (MV2+) were investigated by time resolved absorption spectroscopy. Biexponential behavior of the charge separation is observed and explained by different donor states involved in the electron transfer reaction. Furthermore, we found a linear dependence of the amplitude weighted average electron transfer rate <k ET> on the electron acceptor concentration until a methylviologen saturation limit is reached.

Structure and composition profile of InAs/GaAs quantum dots capped by an InGaAs and InAlAs combination layer

Cross-sectional transmission electron microscopy (X-TEM) and scan-TEM are performed to study how the structural properties of InAs/GaAs quantum dots (QDs) are affected when capped by an InGaAs and InAlAs combination layer (CBL), which currently is one of the most promising active regions for a 1.3 microm QD laser. GaAs capping causes leveling of the QDs, which is suppressed by the introduction of an InGaAs and InAlAs CBL. Scan-TEM results show that the CBL significantly suppresses In segregation and In-Ga intermixing during the capping process. Therefore, the height and In concentration in the buried QDs remain larger than that of GaAs capped QDs, leading to the enhanced optical properties of InAs QDs.