Marco Rossetti

Two-state switching and dynamics in quantum dot two-section lasers

The electrical control of the lasing wavelength in two-section quantum dot lasers is investigated. By changing the optical loss in the absorber section, the control of the ground-state (GS) and excited-state (ES) lasing thresholds and output powers is achieved. Additionally, a complex self-pulsation dynamics with simultaneous oscillations of the GS and ES intensities is observed. The experimental results are well explained in the framework of a rate equation model.

Quantum dot superluminescent diodes emitting at 1.3 /spl mu/m

We report ridge-waveguide superluminescent diodes based on five stacks of self-assembled InAs-GaAs quantum dots. Devices with output powers up to 10 mW emitting around 1.3 /spl mu/m are demonstrated. Spectral analysis shows a broad emission peak (26-nm full-width at half-maximum) from the dot ground state at low injection, and an additional peak from the excited state at higher bias. Temperature characteristics in the range 10/spl deg/C-80/spl deg/C are also reported. The experimental curves are in good agreement with simulations performed using a traveling-wave rate equation model.

Broadband blue superluminescent light-emitting diodes based on GaN

We report on the achievement of III-nitride blue superluminescent light-emitting diodes on GaN substrates. The epitaxial structure includes an active region made of In0.12Ga0.88N quantum wells in a GaN/AlGaN waveguide. Superluminescence under cw operation is observed at room temperature for a current of 130 mA and a current density of 8 kA/cm2. The central emission wavelength is 420 nm and the emission bandwidth is ∼5 nm in the superluminescence regime. A peak optical output power of 100 mW is obtained at 630 mA under pulsed operation and an average power of 10 mW is achieved at a duty cycle of 20%.

Ultrafast gain dynamics in 1.3 μm InAs/GaAs quantum-dot optical amplifiers: the effect of p doping

Ultrafast gain dynamics of the ground-state transition are measured in electrically pumped InAs∕GaAs quantum-dot amplifiers emitting near 1.3μm at room temperature. Gain recovery on a subpicosecond time scale occurs at high electrical injection. However, when comparing p-doped and undoped devices fabricated under identical conditions and operating at the same gain, faster absorption recovery but slower gain dynamics are observed in p-doped amplifiers. The slower gain dynamics is attributed to a reduced reservoir of excited-state electrons in p-doped quantum-dot devices, which limits the recovery of the electron ground-state occupation mediated by intradot carrier-carrier scattering.

Growth and characterization of InAs columnar quantum dots on GaAs substrate

The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by molecular beam epitaxy was investigated. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). It was found that the growth of the CQDs is very sensitive to growth interruption (GI) and growth temperature. Both longer GI and higher growth temperature impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the additional PL peak tails. By properly choosing the GI and the growth temperature, CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period number up to 35 without plastic relaxation were grown. The corresponding equivalent thickness of the SL is 41 nm which is two times higher than the theoretical critical thickness of the strained InGaAs layer with the same average In composition of 16%. The increase of the critical thickness is partially associated with the formation of the CQDs. Based on a five...

High-Power Quantum-Dot Superluminescent Diodes With p-Doped Active Region

We demonstrate the use of p-doping in the active region of quantum-dot superluminescent diodes. Modal gain measurements and light output-current characteristics prove that p-doping is beneficial for achieving higher gain, higher output power, and better temperature stability

Electro-optic and electro-absorption characterization of InAs quantum dot waveguides

Optical properties of multilayer InAs quantum dot waveguides, grown by molecular beam epitaxy, have been studied under applied electric field. Fabry-Perot measurements at 1515 nm on InAs/GaAs quantum dot structures yield a significantly enhanced linear electro-optic efficiency compared to bulk GaAs. Electro-absorption measurements at 1300 nm showed increased absorption with applied field accompanied with red shift of the spectra. Spectral shifts of up to 21% under 18 Volt bias was observed at 1320 nm.

Characterization and Modeling of Broad Spectrum InAs–GaAs Quantum-Dot Superluminescent Diodes Emitting at 1.2–1.3

High-power broadband superluminescent diodes (SLDs) emitting in the 1.2-1.3-mum region are demonstrated using InAs-GaAs quantum dots (QDs). The highest output powers of ~30-50 mW are achieved using 18 QD layers with p-doped GaAs spacers. At these high powers the device operates in a regime of broad bandwidth (~100 nm) with a spectral dip of ~5 dB between two separate peaks originated by the QD ground and excited states. Spectral calculations performed with a traveling-wave rate equation model show excellent agreement with the experimental data and provide design rules for optimizing the output spectrum. SLD characteristics are presented for two different device structures consisting of tilted and bent waveguides. The latter allows the achievement of higher output powers at lower currents. The coherence properties and the temperature characteristics are also discussed in detail.

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We report on the characteristics of blue superluminescent light emitting diodes based on the emission of InGaN quantum wells. Narrow ridge-waveguide devices realized by standard processing techniques and with extremely low facet reflectivity show single lateral mode emission and continuous-wave output powers >35 mW with a typical spectral bandwidth of 4–5 nm. Tuning the composition of the active region, superluminescent light emitting diodes spanning all the spectral range between 410 and 445 nm could be realized. The light output is highly directional and results in a coupling efficiency into single mode fibers >50%. The device temperature behavior is also discussed.

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We demonstrate the feasibility and flexibility of artificial shape engineering of epitaxial semiconductor nanostructures. Novel nanostructures including InGaAs quantum rods (QRs), nanocandles, and quantum dots (QDs)-in-rods were realized on a GaAs substrate. They were formed by depositing a short-period GaAs/InAs superlattice (SL) on a seed QD layer by molecular beam epitaxy growth. The InAs layer thickness in the SL plays an important role in obtaining the QRs. The growth of the QRs is very sensitive to growth interruption and growth temperature. By properly choosing both growth parameters, QRs with length of 41 nm corresponding to an extremely large aspect ratio of 4.1 were obtained. The evolution from a 0-D to 1-D confinement type is evidenced in the optical properties. The origin of the optical transitions from the QRs was understood by calculations of the electronic states within a fully 3-D approach in the eight-band k