InAs-GaAs Quantum Dot Lasers Research Articles

Carrier Dynamics in Self-Assembled InAs QD Laser Structures and Broad-Area InAs QD Lasers Grown by Molecular Beam Epitaxy

ABSTRACTWe investigated carrier dynamics in both proton-irradiated InAs-GaAs quantum dot laser structures and in high power broad-area InAs-GaAs quantum dot lasers with windowed n-contacts using time-resolved PL (TR-PL) techniques.

Self-Heating Effect on the Two-State Lasing Behaviors in 1.3-µm InAs–GaAs Quantum-Dot Lasers

Experimental and theoretical study of the self-heating effect on the two-state lasing behaviors in 1.3-µm self-assembled InAs–GaAs quantum dot (QD) lasers is presented. Lasing spectra under different injected currents, light–current (L–I) curves measured in continuous and pulsed regimes as well as a rate-equation model considering the current heating have been employed to analyze the ground-state (GS) and excited-state (ES) lasing processes. We show that the self-heating causes the quenching of the GS lasing and the ES lasing by the increased carrier escape rate and the reduced maximum modal gain of GS and ES.

Carrier Relaxation and Modulation Response of 1.3-$\mu$m InAs–GaAs Quantum Dot Lasers

A self-consistent rate equation model is presented to investigate the influence of carrier relaxation on the modulation response of 1.3 mum InAs-GaAs quantum dot lasers. In this model, the carrier dynamics in GaAs barrier, relaxation pathways, and the phonon- and Auger-assisted relaxation are considered. The dependence of 3 dB bandwidth on the relaxation time and relaxation pathway is discussed. It is shown that carrier relaxation via less energy level has better carrier confinement and higher 3 dB bandwidth. The improvement of bandwidth by tunnelling injection QD structure is investigated from the point of view of relaxation pathway. The different effects of tunnelling into ground state and excited state on the 3 dB bandwidth are analyzed. The enhanced carrier relaxation by p-type modulation doping and its effect on the bandwidth are investigated. It is found that there exists a tradeoff on the improvement of bandwidth by p-doping, which is explained as the competition between the bandwidth limitation of K -factor and relaxation dynamics. Increase in the bandwidth of QD lasers by improving both the carrier relaxation dynamics and K-factor limitation is discussed.

Spectral Analysis of 1.55-$\mu$m InAs–InP(113)B Quantum-Dot Lasers Based on a Multipopulation Rate Equations Model

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs-InP(113)B quantum dot (QD) lasers emitting at 1.55 mum. The numerical model is based on a multipopulation rate equations analysis. Calculations take into account the QD size dispersion as well as the temperature dependence through both the inhomogeneous and the homogeneous broadenings. This paper demonstrates that the model is capable of reproducing the spectral behavior of InAs-InP QD lasers. Especially, this study aims to highlight the transition of the lasing wavelength from the ground state (GS) to the excited state (ES). In order to understand how the QD laser turns on, calculated optical spectra are determined for different cavity lengths and compared to experimental ones. Unlike InAs-GaAs QD lasers emitting at 1.3 mum, it is shown that a continuous transition from the GS to the ES is exhibited because of the large inhomogeneous broadening comparable to the GS and ES lasing energy difference.

Temperature Sensitivity Dependence on Cavity Length in p-Type Doped and Undoped 1.3-$\mu$m InAs–GaAs Quantum-Dot Lasers

We have fabricated 1.3-mum InAs-GaAs quantum-dot (QD) lasers with and without p-type modulation doping and their characteristics have been investigated. We find that introducing p-type doping in active regions can improve the temperature stability of 1.3-mum InAs-GaAs QD lasers, but it does not increase the saturation modal gain of the QD lasers. The saturation modal gain obtained from the two types of lasers is identical (17.5 cm-1 ). Moreover, the characteristic temperature increases as cavity length increases for the two types of lasers, and it improves more significantly for the lasers with p-type doping due to their higher gain.

Gain Compression and Above-Threshold Linewidth Enhancement Factor in 1.3-$\mu\hbox{m}$ InAs–GaAs Quantum-Dot Lasers

Quantum-dot (QD) lasers exhibit many useful properties such as low threshold current, temperature and feedback insensitivity, chirpless behavior, and low linewidth enhancement factor (alpha <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> -factor). Although many breakthroughs have been demonstrated, the maximum modulation bandwidth remains limited in QD devices, and a strong damping of the modulation response is usually observed pointing out the role of gain compression. This paper investigates the influence of the gain compression in a 1.3-mum InAs-GaAs QD laser and its consequences on the above-threshold alpha <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> -factor. A model is used to explain the dependence of the alpha <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> -factor with the injected current and is compared with AM/FM experiments. Finally, it is shown that the higher the maximum gain, the lower the effects of gain compression and the lower the alpha <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> -factor. This analysis can be useful for designing chirpless QD lasers with improved modulation bandwidth as well as for isolator-free transmission under direct modulation.

Rate Equations for 1.3-&lt;tex&gt;$mu$&lt;/tex&gt;m Dots-Under-a-Well and Dots-in-a-Well Self-Assembled InAs–GaAs Quantum-Dot Lasers

A rate-equation model, in which three discrete quantum-dot (QD) energy levels are assumed and all possible relaxation paths and carrier transport in the GaAs barrier are considered, is presented to analyze the steady-state performance of 1.3 mum undoped and doped dots-under-a-well (DUW) and dots-in-a-well (DWELL) InAs-GaAs QD lasers. DWELL QD lasers have higher saturation value of QD level occupation probabilities and characteristic temperature (T0) than that of DUW QD lasers due to the improvement of hole confinement. The p-doped QD laser shows lower threshold current density than n-doped QD laser at the same threshold condition, and the T0 of n-doped DWELL laser is higher than that of p-doped DWELL laser at room temperature. Optimized QD layer number of DUW and DWELL QD lasers with different QD density is discussed

High extinction ratio and high-temperature 2.5-Gb/s floor-free 1.3-/spl mu/m transmission with a directly modulated quantum dot laser

For the first time with a directly modulated InAs-GaAs quantum-dot laser, high extinction ratio (up to 17 dB) and 25degC-85degC single-mode-fiber data floor-free transmissions are achieved at 2.5 Gb/s. Moreover, an interferometric technique showed a nearly constant Henry factor ~2 until a bias current six times the threshold current

High-performance three-layer 1.3-/spl mu/m InAs-GaAs quantum-dot lasers with very low continuous-wave room-temperature threshold currents

The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR)-coated facets has been utilized to obtain low threshold currents and threshold current densities for 1.3-μm multilayer InAs-GaAs quantum-dot lasers. A very low continuous-wave (CW) room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are achieved for a three-layer device with a 1-mm HR/HR cavity. For a 2-mm cavity, the CW threshold current density is as low as 17 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets.

Near-ideal InAs QDs on GaAs substrates for 1.3–1.5m laser applications

1.3–1.5µm Quantum dot (QD) lasers on GaAs substrates demonstrate near-ideal device parameters. Pseudomorphic 1.3µm InAs-GaAs QD lasers demonstrate low threshold current density (Jth300K < 100A/cm2), high differential efficiency (ηdiff > 80%), and low losses (α < 1.5cm–1 all realized in the same device. Characteristic temperature for the threshold current is ∼170K up to 70°C. Reduced linewidth enhancement factor is advantageous for low-chirp operation and makes it possible to suppress completely beam filamentation up to stripe widths ∼100µm. GaAs-based 1.3µm QD vertical-cavity surface-emitting lasers (VCSELs) with 8µm oxide aperture emit up to 2mW single mode continuous wave (CW) optical power. Metamorphic 1.5µm QD lasers on GaAs substrates with high quantum efficiency (ηi > 60–70%) and low losses (α < 3–4cm–1 and operating at power levels beyond 7W are fabricated.