Dephasing times in quantum dots due to elastic LO phonon-carrier collisions

Interpretation of experiments on quantum dot (QD) lasers presents a challenge: the phonon bottleneck, which should strongly suppress relaxation and dephasing of the discrete energy states, often seems to be inoperative. We suggest and develop a theory for an intrinsic mechanism for dephasing in QD's: second-order elastic interaction between quantum dot charge carriers and LO-phonons. The calculated dephasing times are of the order of 200 fs at room temperature, consistent with experiments. The phonon bottleneck thus does not prevent significant room temperature dephasing.Comment: 4 pages, 1 figure, accepted for Phys. Rev. Let

Ensemble interactions in strained semiconductor quantum dots

Large variations in InxGa1-xAs quantum dot concentrations were obtained with simultaneous growths on vicinal GaAs [001] substrates with different surface step densities. It was found that decreasing dot-dot separation blueshifts all levels, narrows intersublevel transition energies, shortens luminescence decay times for excited states, and increases inhomogeneous photoluminescence broadening. These changes in optical properties are attributed to a progressive strain deformation of the confining potentials and to the increasing effects of positional disorder in denser dot ensembles

Ultrafast laser micro-nano structuring of transparent materials with high aspect ratio

Ultrafast lasers are ideal tools to process transparent materials because they spatially confine the deposition of laser energy within the material's bulk via nonlinear photoionization processes. Nonlinear propagation and filamentation were initially regarded as deleterious effects. But in the last decade, they turned out to be benefits to control energy deposition over long distances. These effects create very high aspect ratio structures which have found a number of important applications, particularly for glass separation with non-ablative techniques. This chapter reviews the developments of in-volume ultrafast laser processing of transparent materials. We discuss the basic physics of the processes, characterization means, filamentation of Gaussian and Bessel beams and provide an overview of present applications

Spin relaxation in charged InAs/GaAs quantum dots

Photoexcited electron and hole spin relaxation has been studied in modulation doped InAs/GaAs self-assembled quantum dots by means of time resolved photoluminescence. The electron spin relaxation times of 50 to 70 ps have been found for the undoped and p-doped samples, while the hole spins randomise on a much shorter time scale. Electrons preserve their spin orientation during capture and relaxation for excitation into the barriers, however, no preferential spin polarisation has been detected for carrier excitation directly into the dots

Spin relaxation in charged InAs/GaAs quantum dots

Photoexcited electron and hole spin relaxation has been studied in modulation doped InAs/GaAs self-assembled quantum dots by means of time resolved photoluminescence. The electron spin relaxation times of 50 to 70 ps have been found for the undoped and p-doped samples, while the hole spins randomise on a much shorter time scale. Electrons preserve their spin orientation during capture and relaxation for excitation into the barriers, however, no preferential spin polarisation has been detected for carrier excitation directly into the dots

Carrier dynamics in modulation-doped InAs GaAs quantum dots

Photoexcited carrier dynamics was studied in n and p modulation-doped self-assembled InAs GaAs quantum dots by means of time-resolved photoluminescence with excitation and detection energies varied through barrier, wetting layer, and quantum dot states. Carrier transfer to the ground state of the dots was found to occur within 5 to 6 and 12 ps for the doped and undoped samples, respectively. The experiments suggest that in all samples the carrier capture into the highest quantum dot levels proceeds by phonon emission. The significant difference in the transfer times is attributed to different relaxation mechanisms for the subsequent process of intradot carrier relaxation. For the doped samples, the presence of built-in carriers in the dots leads to efficient electron-hole scattering, while in the undoped structure scattering by phonons is identified as the main relaxation channel. Additionally, experimental results show decreased carrier lifetimes in the doped structures, which is attributed to nonradiative recombination at doping-induced recombination centers in the vicinity of the quantum dot layers

Carrier spin dynamics in modulation-doped InAs/GaAs quantum dots

Photoexcited electron and hole spin relaxation was studied in modulation-doped and undoped InAs/GaAs quantum dots by means of time-resolved photoluminescence. After excitation into the barriers or the wetting layer, the electron spin polarization is preserved during the capture and relaxation in the dots, especially in the p-doped structures, and decays with a characteristic time of about 100 ps. Spin state admixture in combination with electron interaction with acoustic phonons is suggested as the spin relaxation mechanism. Rapid spin polarization decay during carrier relaxation in undoped quantum dots is attributed to electron-optical phonon interaction. For carrier excitation directly into the dots, no significant spin polarization was observed, which points to the mixed nature of hole levels in quantum dots. The hole spin polarization randomizes on a much shorter time scale and is not detected in the experiment