[Show abstract][Hide abstract] ABSTRACT: We present a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure. They show that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude-phase coupling enable a significant improvement of beam quality compared to quantum-well lasers of identical geometry. Near-field profiles and beam quality (M-2) parameters calculated on the basis of time-dependent effective Maxwell-Bloch equations into which the physical properties of the active media are included via space-dependent material parameters, effective time constants, and matrix elements are fully confirmed by experimental measurements. Together they indicate that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude-phase coupling enable a significant improvement of beam quality compared with quantum-well lasers of identical geometry. (C) 2004 American Institute of Physics.
[Show abstract][Hide abstract] ABSTRACT: Comparative near-field and beam-quality (M2) measurements on narrow stripe quantum-dot (QD) and quantum-well (QW) lasers of identical structure, both emitting at 1100 nm, are presented. Intrinsic suppression of filamentation in the QD lasers is observed. QD lasers emitting at 1300 nm again show no filamentation. For a 6-mum-stripe, QW laser, M2 increases from 2.6 to 6.1 with output power increasing from 5 to 60 mW and with increasing stripe width (20 mW, 3-->10 mum, M2=2.6-->4.7). In the QD lasers, filamentation is suppressed up to 8 mum (1100 nm) and 9 mum (1300 nm) stripe width and no dependence on output power is observed.
[Show abstract][Hide abstract] ABSTRACT: 4.7 W continuous-wave (CW) and 11.7 W quasi-CW output power have
been demonstrated for laser diodes based on six-fold stacks of
InGaAs/GaAs quantum dots. Lifetimes beyond 3000 h at 1.0 and 1.5 W
output power and 50°C heatsink temperature were measured. The output
power is limited by catastrophic optical mirror damage occurring at 19.5
MW/cm<sup>2</sup> on the front facet
[Show abstract][Hide abstract] ABSTRACT: Temporally resolved longitudinal mode dynamics for sixfold stacked short cavity quantum-dot lasers is investigated in the mus time range. Results are presented for 10, 20, and 50 mum wide stripes at room temperature and at 100 K. After turn-on a redshift of single longitudinal modes, a blueshift of the mode groups and a redshift of the mean value of the spectra are observed simultaneously. Temperature dependent leakage loss spectra due to leaky substrate modes are calculated. The blueshift of the mode grouping, predicted by the theory, is in good agreement to the experimental data.
[Show abstract][Hide abstract] ABSTRACT: Temporally resolved longitudinal mode dynamics for 6-fold stacked short cavity quantum dot (QD) lasers is investigated in the μsec time-range. Measurements were performed at room temperature and at 100K. After turn-on a red-shift of single longitudinal modes, a blue-shift of the mode groups and a red shift of the mean value of the spectra are observed simultaneously. Temperature dependent leakage loss spectra due to leaky substrate modes are calculated. The blue shift of the mode-grouping, predicted by the theory, is in good agreement with the experimental data.
Indium Phosphide and Related Materials Conference, 2002. IPRM. 14th; 02/2002
[Show abstract][Hide abstract] ABSTRACT: By forming twin contacts on a 1300 nm quantum dot laser, a small signal modulation bandwidth of 4.6 GHz is achieved. This bandwidth value is 2.3 times greater than that for the equivalent single contact device. The quantum dot lasers studied are 800 μm long with 8 μm wide ridge guides and 5 InAs quantum dot stacks in the active layer.
Lasers and Electro-Optics Society, 2002. LEOS 2002. The 15th Annual Meeting of the IEEE; 02/2002
[Show abstract][Hide abstract] ABSTRACT: Semiconductor heterostructures with size quantization of carriers in all three directions, or quantum dots (QDs), open a new era in device engineering. An important breakthrough occurred when the self-organised growth approach had been refined to such an extent, that defect-free QDs made with these technique exhibited properties predicted for zero-dimensional structures. Their practical application in devices, first of all lasers, became possible. When used for active layers in injection lasers differential gain is strongly increased potentially providing improved dynamic properties. The cut-off frequencies larger than 10 GHz are presently demonstrated. The saturation material gain is as high as 15 × 104 cm—1 as compared to QW values of about 3 × 103 cm—1. The wavelength dependence of gain is best described by Master equations of microstates. High internal (>96%) and differential (70%) efficiencies at 300 K and output power up to 4 W are realized now for QD lasers emitting in the 0.94–1.15 μm range. Transparency current density of 18 A/cm2 has been recently demonstrated at 1.15 μm. GaAs-based QD lasers emit near 1.3 μm with Jth = 70 A/cm2 (L = 1.9 mm, 300 K) and CW output power of ∼3 W. In narrow (7 μm) stripes almost chirp-free operation and relaxation oscillations at 2.4 GHz (L = 400 μm) are manifested. Differential efficiency is 55% and internal losses are 1.5 cm—1. 1.3 μm GaAs-based QD VCSELs (300 K, Ith = 1.8 mA, ηdiff > 40%) are realized.
[Show abstract][Hide abstract] ABSTRACT: Improved device characteristics of high-power InGaAs/GaAs quantum dot (QD) lasers are presented. An ideal internal quantum efficiency close to 100%, very low transparency current density of 18 A/cm2 and a peak power close to 4 W at 1155 nm lasing wavelength in pulsed operation at room temperature are demonstrated. The improvement of the devices is mainly due to the reduction of non-radiative recombination centres in the GaAs matrix around the dots. The lasing spectra for different driving currents are presented and compared to theoretical calculations based on master equations for the micro-states (MEM) coupled to the rate equations for the photon density. From the maximum width of the lasing spectra under high driving currents (18 nm) the fraction of QDs that contribute to the lasing emission is deduced. For different lasers the maximum ground (excited) state gain is found to be 13.6 cm—1 (34 cm—1), respectively, via a fit of the QD gain-current dependence according to the MEM theory.
[Show abstract][Hide abstract] ABSTRACT: The gain spectra of QD lasers are measured using the electrical stripe length method. Large modal gain of >20 cm—1 per QD sheet is found. The spectra reflect the theoretically predicted change of the carrier distribution function from non-thermal to thermal with increasing temperature.
[Show abstract][Hide abstract] ABSTRACT: Using of structures with size quantization in all three directions, or quantum dots (QD's) allows exciting possibilities in device engineering. Semiconductor heterostructures with self-organized QDs have experimentally exhibited properties expected for zero-dimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold current, and to provide improved dynamic properties. Optimization of deposition parameters can ensure that the self-organized islands are small (~10 nm), have a similar size and shape and form dense arrays. Saturation material gain as high as 150000 cm-1 as compared to QW values of about 3000 cm-1. Maximum differential gain reported for QD lasers approaches 10-12 cm2 and exceeds the QW laser values by about three orders of magnitude. Direct observation of relaxation oscillations reveals present cutoff frequencies close to 10 GHz. High internal (>96%) and differential (70%) efficiencies at 300 K are realized for QD lasers emitting in the 0.94-1.15 mum range. GaAs-based lasers for the 1.3 mum range with low Jth(80 A/cm2, cavity length 1.9 mm) at room temperature (RT) are realized using InAs/InGaAs/GaAs QDs obtained by activated spinodal decomposition. Differential efficiency is 55% and internal losses are 1.5 cm-1. 3W CW operation at RT is achieved. 1.3 mum GaAs-based QD VCSELs (300 K, Ith=1.8 mA, εdiff>40%) are realized. .
[Show abstract][Hide abstract] ABSTRACT: The influence of high energy proton irradiation on the device
properties of InGaAs/GaAs quantum dot and quantum well lasers has been
investigated. In the regime of spontaneous emission, quantum dot lasers
show a much enhanced radiation hardness compared to quantum well lasers,
manifested in a smaller increase of threshold current density. However,
in the lasing regime the device characteristics are similarly
influenced. Internal differential quantum efficiencies are reduced,
internal optical losses remain constant
[Show abstract][Hide abstract] ABSTRACT: Methods to re-establish a flat growth front on top of the corrugated surface of InGaAs quantum dots (QDs) during MOCVD are reported. Overgrowth temperatures at least 100 K higher than the low QD deposition temperature of 490°C are required for a reduction of the corrugation. In order to avoid degradation of the QDs, however, the temperature must not be increased unless the QDs are buried by ∼3 nm GaAs deposited at the QD growth temperature. Application of an additional annealing step after deposition of the GaAs cap layer improves the surface flatness and leads to an improvement of the radiative recombination efficiency. Lasers grown using such an annealing process for GaAs spacers of an InGaAs QD stack show lower threshold currents and higher internal quantum efficiency.
[Show abstract][Hide abstract] ABSTRACT: The optical and electronic properties of self-organized quantum dots (QDs) are of decisive importance for the performance of laser diodes with such QDs as the active medium. Of primary interest is the gain with regard to its spectral position, width, magnitude, and temporal behavior. We survey the mutually stimulating advances in the theoretical understanding of QD gain and the performance of QD lasers. Emphasis is put on the temperature dependence of the carrier distribution function.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate quantum dot lasers at 1140 nm with record high optical output power of 5 W. The use of novel tunneling barriers allows us to improve the characteristic temperature, T<sub>0</sub>. A detailed investigation is presented of the impact of barrier design on the characteristic temperature for QD lasers. The quantum dot lasers were grown by low-pressure Metalorganic Chemical Vapor Phase Deposition (MOCVD). The active layer consists of stacks of InGaAs quantum dots in a GaAs matrix. Ridge waveguide lasers with 200 μm stripe-width exhibit a total optical output power up to 5 W in pulsed operation at room temperature
[Show abstract][Hide abstract] ABSTRACT: High-power semiconductor laser diodes based on multiple InGaAs/GaAs quantum-dot layers grown by metal-organic chemical-vapor deposition are demonstrated. The devices exhibit a peak power of 3 W (4.5 W) at 1100 nm (1068 nm), respectively, during pulsed operation at room temperature and show slope efficiencies of 57% (66%).
[Show abstract][Hide abstract] ABSTRACT: The field of semiconductor quantum dot (QD) diode lasers is rapidly developing. Important milestones, such as low-threshold
operation and room-temperature cw operation, have been achieved in the last years. We review the progress in theoretical understanding
and present recent results on high-power QD laser operation (>3W@1100nm).
Applied Physics B 11/1999; 69(5):413-416. DOI:10.1007/s003400050828 · 1.86 Impact Factor