Layer Of Self-organized Quantum Dots Research Articles

Ultrafast gain dynamics in quantum-dot amplifiers: theoretical analysis and experimental investigations

Ultrafast gain dynamics in an optical amplifier with an active layer of self-organized quantum dots (QDs) emitting near 1.3 /spl mu/m is characterized experimentally in a pump-probe experiment and modeled theoretically on the basis of QD Maxwell-Bloch equations. Experiment and theory are in good agreement and show ultrafast subpicoseconds gain recovery followed by a slower 5 ps recovery. This behavior is found to be mainly caused by longitudinal optical phonon scattering and strongly dependents on electronic structure and confinement energy of the dots. A low amplitude-phase coupling (/spl alpha/ factor) is theoretically predicted and demonstrated in the experiments. The fundamental analysis reveals the underlying physical processes and indicates limitations to QD-based devices.

Many-Particle Charging Effects and Recombination Current through a Quantum Dot Array

A numerical analysis of the stationary current–voltage characteristic of a p–i–n diode comprising a layer of self-organized quantum dots is presented. For bias voltages below the flat band condition the current is given by sequential tunneling of holes and electrons in the quantum dots and the wetting layer. Their recombination causes a current through the device which shows well-pronounced differential conductance oscillations. As a fingerprint of many-particle charging effects in individual quantum dots we discuss these oscillations in terms of the strength of the Coulomb interaction between carriers in different quantum dots and the influence of the size distribution of the quantum dots.

High efficiency (ηD>80%) long wavelength (λ>1.25 μm) quantum dot diode lasers on GaAs substrates

Diode lasers based on several layers of self-organized quantum dots (QD) on GaAs substrates were studied. The lasing wavelength lies in the range λ=1.25–1.29 μm, depending on the number of QD layers and optical losses. A record external differential efficiency of 88% and the characteristic temperature of threshold current, 145 K, were obtained. The internal losses, and also threshold and spectral characteristics, are correlated with the optical gain and radiative recombination efficiency, which are strongly dependent on the design of the active region and growth modes.

Vertical transport through laterally periodically modulated heterostructures

The ballistic transport in a laterally periodically modulated heterojunction connecting two reservoirs is studied: this can model the presence of an ordered layer of self-organized quantum dots. The problem is solved in the envelope function formalism using a three-dimensional (3D) generalization of the transfer matrix approach that exploits the two-dimensional (2D) lattice periodicity. Illustrative numerical results are presented showing qualitatively different behaviors of the transmission coefficients due to the multichannel nature of the propagation. In particular, deep minima of the transmission occur due to destructive interference between different conducting channels, a situation that cannot be realized in the absence of the lateral modulation.