This paper reports on transient switch-off of the emission of an electrically pumped quantum dot laser with perturbation by a short optical pulse. This laser response is explained in terms of hot carrier absorption on intraband optical transitions leading to the transient suppression of the laser mode and, hence, to the switch-off. The switching time constant is determined to be as fast as 2 ps.

We investigate quantum-dot (QD) lasers in an external cavity using Littrow and Littman configurations. Here, we report on a continuously tunable QD laser with a broad tuning range from 1047 to 1130 nm with high stability and efficient side mode suppression. The full-width at half-maximum of the laser line is 0.85 nm determined mainly by the quality of the external grating. This laser can be operated in a dual-mode modus, where the mode-spacing can be tuned continuously between 1.1 and 34 nm. Simultaneous emission of the two laser modes is shown by sum frequency generation experiments.

A study of the electron-hole relaxation dynamics in metalorganic chemical vapour deposition (MOCVD)-grown InGaAs/GaAs quantum dots (QDs) emitting at 1.3 mum is presented. The photoluminescence (PL) rise and decay times are measured as functions of carrier density and temperature, showing that the electron-hole relaxation into the QD ground state occurs within a few picoseconds. We find that the emission of two longitudinal optical (LO) phonons is the dominant capture process at room temperature, whereas carrier-carrier scattering dominates the relaxation process at low temperatures and high carrier densities. Finally, the MOCVD-grown QD structures show relatively small PL quenching; the quenching is caused by thermal carrier escape from the QD ground state via absorption of two LO phonons.

Summary form only given. In this paper, we show the generation of sub-10 ps optical pulses by optical synchronous pumping of a QD laser coupled to an external cavity. The QD laser is a ridge waveguide laser structure with a length of 1.7 mm and a mesa width of 5 /spl mu/m. In the active material, 7 layers of InAs QDs (dot coverage: 10/sup 11/ cm/sup -2/) are embedded in GaAs and are surrounded by an AlGaAs waveguide. This structure is pumped optically by 100 fs pulses from a mode-locked Ti:sapphire laser (excitation wavelength: 800 nm, repetition frequency: 80 MHz) that is focused onto the ridge with a cylindrical lens. Together with the tunability of the emission wavelength such devices are promising candidates for fiber optic communication.

We report on the subpicosecond switch-off of the emission of an electrically pumped quantum-dot (QD) laser with perturbation by a 100 fs optical pulse. The observed effect is in contrast to known ones for quantum-well laser diodes. This is explained by unique properties of the QDs, namely by the fast modal gain saturation and localization-enhanced intraband absorption. The QD laser response can be described in terms of hot carrier absorption in the barrier states via intraband optical transitions leading to the transient suppression of the laser mode and, hence, to the switch-off. (C) 2002 American Institute of Physics.

Summary form only given. The gain spectrum of semiconductor quantum dots (QDs) is inhomogeneously broadened due to inevitable dot size fluctuations. If the homogeneous broadening is small, only QDs of the same size interact with each other via the photon field and lasing can occur on many wavelengths simultaneously. In this respect, the system QD/barrier material resembles a guest/host-system, much like titanium ions in a sapphire crystal. Therefore, QD lasers might be interesting candidates for mode locking. We investigate the lasing dynamics of an optically pumped gain-switched edge emitting QD laser at room temperature. The laser structure is a Fabry-Perot resonator of length L = 1.6 mm with cleaved uncoated end facets. The active material consists of 7 layers of InAs QDs embedded in GaAs and surrounded by an AlGaAs waveguide The GaAs surrounding the QDs is optically pumped with 100 fs pulses from a regenerative amplifier at an excitation wavelength of 800 nm. Lateral gain guiding is enforced by focussing the beam to a stripe of 100 /spl mu/m width, along the full length of the laser resonator. The emission from the edge of the sample is measured both time-integrated with a germanium diode and time-resolved by upconversion.

We investigate the ultrafast carrier dynamics in metalorganic chemical vapor deposition-grown InGaAs/GaAs quantum dots emitting at 1.3 μm. Time-resolved photoluminescence upconversion measurements show that the carriers photoexcited in the barriers relax to the quantum-dot ground state within a few picoseconds. At low temperatures and high carrier densities, the relaxation dynamics is dominated by carrier–carrier scattering. In contrast, at room temperature, the dominant relaxation process for electrons is scattering between quantum-dot levels via multiple longitudinal optical (LO)-phonon emission. The reverse process, i.e., multiple LO-phonon absorption, governs the thermal re-emission of electrons from the quantum-dot ground state.

In this paper, we investigate the dynamics of amplified spontaneous emission (ASE) in Self-assembled InAs/GaAs quantum dots. Upconversion is used to time-resolve the emission from an edge-emitting waveguide structure at room temperature which is excited by short laser pulses in a stripe geometry. We demonstrate that increases in both the electron-hole pair density and the stripe length significantly decrease the emission decay time from around 2 ns, corresponding to spontaneous emission, to about 0.9 ns, corresponding to stimulated emission or ASE. A simulation of the ASE process in this geometry is in agreement with our experimental results.

We investigate carrier capture processes in strain-induced quantum dot structures. The quantum dots consist of a near-surface InGaAs/GaAs quantum well in which a lateral confining potential is generated by the strain from InP stressor islands grown on the sample surface. Using photoluminescence spectroscopy, we show that the rate of carrier capture into the quantum dots increases dramatically when the energetic depth of the confinement potential is reduced by enlarging the quantum well/surface separation D. While carriers in the quantum well region between the quantum dots are found to experience D-dependent nonradiative surface recombination, this process seems to be negligible for carriers in the quantum dots, presumably due to the protecting InP islands.

The transition from sputtered Al to electroplated Cu interconnects for future microelectronic devices has led to an interest in understanding the relationships between the microstructure and texture of Cu that might impact electrical performance, similar to what has been done for Al. Electroplated Cu undergoes a recrystallization at room temperature that is related to the presence of organic and inorganic additives in the plating bath. As plated, the Cu grains are small (approx. 0.1 μm) and equiaxed, but over a period of hours to days, recrystallization results in grains several microns in size. We observe a significant weakening of the strong as-plated (111) texture by x-ray diffraction pole figure measurements and an increase in the level of randomness. We propose that multiple twinning is the leading mechanism for this phenomenon.

We investigate the dynamics of amplified spontaneous emission (ASE) in self-assembled InAs/GaAs quantum dots, using pulsed optical excitation of an edge-emitting sample at room temperature. A material gain of 1.5×104 cm−1 is determined for 800 nm excitation with 1.5 μJ/cm2 pulses. Using photoluminescence up-conversion, we show that increases in both electron–hole pair density and photon density in the excited stripe cause a significant decrease in the decay time from 2.2 ns, corresponding to spontaneous emission, to about 0.9 ns, corresponding to stimulated emission or ASE. A carrier capture time of 10 ps limits the onset of the ASE process for short stripe lengths.

Summary form only given. Self-assembled semiconductor quantum dots have found interest as gain materials for semiconductor lasers. While time-resolved studies on quantum dots have mainly focused on the spontaneous recombination dynamics, little is known about the dynamics of lasing and stimulated emission from the dots. In this contribution we investigate the dynamics of stimulated emission in self assembled InAs-GaAs quantum dots. The sample studied here consists of 7 layers of self assembled InAs quantum dots embedded in GaAs. This active layer is sandwiched in between two 1.2 /spl mu/m thick AlGaAs layers, resulting in a waveguide structure.

The crystallographic texture of electroplated Cu in damascene trenches has been examined by x-ray diffraction pole figure analysis. The influence of two post-plating treatments on the resulting orientation of (111) planes of the Cu inside the trenches are compared. When the as-deposited small-grained Cu is allowed to recrystallize at room temperature before chemical mechanical polishing of the overlying Cu, we observe only a (111) fiber texture of the Cu inside the trenches. In contrast, when the overlying material is polished away before recrystallization of the small-grained Cu, pole figures show evidence of sidewall texture of the (111) planes in addition to the (111) fiber texture in the as-deposited as well as the annealed state. The presence or absence of a sidewall texture component in the pole figures offers insight into the evolution of the microstructure of damascene Cu.

Electroplated Cu films undergo a remarkable recrystallization at room temperature that has been associated with dislocations and defects arising from the influence of surface-active additives during plating. In the process of plating, the composition of the bath changes as the organic additives are depleted by incorporation into the Cu films or electrolytic decomposition and replenished by fresh additions. Given the sensitivity of the plating process to low concentrations of additives, the properties of the plated Cu might be expected to differ between a freshly prepared bath and an older bath that has processed thousands of wafers and achieved a steady state composition of additives and by-products. In this paper we compare the recrystallization rates of Cu films deposited from two such baths on wafers with damascene trenches of widths from 0.3 to 5 μm. Films deposited from the older bath consistently recrystallize at a faster rate for all trench widths and both barrier materials (Ta, TaN) studied. The concentration of impurities is comparable in the two films. Therefore, the difference in rates is likely due to a difference in defect densities in the film due to different adsorbate/surface interactions during plating. Although the recrystallization rates vary, X-ray diffraction pole figure analysis of films plated from the two baths show no differences in texture. Sidewall growth components are visible in both sets of samples. Data on the influence of the barrier material and trench width on recrystallization rates are also presented.

As-electroplated copper undergoes a gradual recrystallization at room temperature related to the plating chemistry. The influence of damascene topography on the recrystallization as well as on the texture of Cu must be understood to optimize properties for superior interconnect performance. A low-temperature anneal before CMP stabilizes the Cu microstructure and eliminates the (111) sidewall growth component that is observed if the overlying Cu is removed before recrystallization.