Numerical study on InGaAsN/GaAs multiple-quantum-well laser with GaAsP and GaAsN barriers

In this work, the multiple-quantum-well InGaAsN laser structures with indirect-GaAsP and direct-GaAsN barriers are investigated by using LASTIP simulation program. We vary the quantum-well number, from 1 to 5, to find appropriate barrier material for InGaAsN laser structures. The simulation results show that InGaAsN laser structure has higher characteristic temperature regardless of what quantum-well number is if the indirect-GaAsP barrier is utilized. Furthermore, for InGaAsN laser structure, the usage of indirect-GaAsP barrier is beneficial for reducing the threshold current when the quantum-well number is from 1 to 2 and the usage of direct-GaAsN barrier is beneficial for reducing the threshold current when the quantum-well number is from 3 to 5.     

Optical characterization of InGaAsN/GaAsN/GaAs quantum wells with InGaP cladding layers

Optical properties of InGaAsN/GaAs and InGaAsN/GaAsN/GaAs quantum well structures with InGaP cladding layers were studied by photoreflectance at various temperatures. The excitonic interband transitions of the InGaAsN/GaAsN/GaAs QW systems were observed in the spectral range above hν=E_g(InGaAsN). The confinement potential of the system with strain compensating GaAsN barriers became one step broader, thus more quantum states and larger optical transition rate were observed. A matrix transfer algorithm was used to calculate the subband energies numerically. Band gap energies, effective masses were adopted from the band anti-crossing model with band-offset values adjusted to obtain the subband energies to best fit the observed optical transition features. A spectral feature below and near the GaAs band gap energy from GaAs barriers is enhanced by the GaAs/InGaP interface space charge accumulation induced internal field.     

Numerical study on gain and optical properties of AlGaInAs, InGaNAs, and InGaAsP material systems for 1.3-μm semiconductor lasers

In reference to real devices fabricated in laboratories, the optical properties of AlGaInAs, InGaNAs, and InGaAsP semiconductor material systems for 1.3-μm semiconductor lasers are systematically studied. Simulation results show that both the AlGaInAs/InP and InGaNAs/GaAs material systems have better gain performance and smaller transparency carrier density than the InGaAsP/InP material system. For the AlGaInAs/InP material system, the characteristic temperature is improved by using compensating tensile strain in barrier. Specifically, for a 250-μm-long short-cavity AlGaInAs/InP laser, when the barrier is with a compensating tensile strain of 0.39%, the characteristic temperatures in 290-330 K and 330-350 K can be enhanced to 121.7 K and 58.9 K, respectively. For the InGaNAs/GaAs material system, simulation results suggest that the laser performance can be significantly improved when the laser is with strain-compensated GaNAs barriers.     

GaAsN/AlAs/AlGaAs double barrier quantum wells grown by molecular beam epitaxy as an alternative to infrared absorption below 4 μm

In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed.     

1.3-μm GaInAsP/InP Multi-Quantum-Well Surface-Emitting Lasers

A multi-quantum-well (MQW) active layer has been introduced to 1.3-μm GaInAsP/InP surface-emitting (SE) lasers. Room temperature pulsed operation of a 1.3-μm MQW SE laser was obtained for the first time and its threshold current was 15 mA. CW (continuous wave) operation up to 7°C (threshold current 1_th=7.6 mA at 7°C) was achieved.     

1.3 m m InGaAsN/ GaAs Lasers Grown by MOCVD Using TBAs and DMHy Sources

We have demonstrated InGaAsN/ GaAs single quantum well (SQW) lasers grown by MOCVD using TBAs and DMHy sources. For un-buffer-strained InGaAsN/ GaAs system, our SQW lasers of 1.3 m m range is among the best in terms of transparency and threshold current density.     

Tuning of long-wavelength emission in InxGa1−xAs quantum dot structures

This work explores the conditions to obtain the extension of the PL emission beyond 1.3 μm in InGaAs quantum dot (QD) structures growth by MOCVD. We found that, by controlling the In incorporation in the barrier embedding the QDs, the wavelength emission can be continuously tuned from 1.25 μm up to 1.4 μm at room temperature. However, the increase in the overall strain of the structures limits the possibility to increase the maximum gain in the QD active device, where an optical density as high as possible is required. By exploring the kinetics of QD surface reconstruction during the GaAs overgrowth, we are able to obtain, for the first time, emission beyond 1.3 μm from InGaAs QDs grown on GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm and significant improvements in terms of line shape narrowing and room temperature efficiency are obtained. The temperature-dependent quenching of the emission efficiency is reduced down to a factor of 3, the best value ever reported for QD structures emitting at 1.3 μm.     

Temperature Dependence of the Threshold Current and the Lasing Wavelength in 1.3-μm GalnNAs/GaAs Single Quantum Well Laser Diode

Temperature stability of the threshold current and the lasing wavelength is investigated in a 1.3-μm GaInNAs/ GaAs single quantum-well laser. The measured characteristic-temperature was 88 K. The small wavelength shift per change in temperature of 0.35 nm/°C was obtained, indicating the superior lasing-wavelength stability. Therefore, it is shown experimentally that GaInNAs is very promising material for the fabrication of light source with excellent high-temperature performance for optical fiber communications.     

Optimization and Characterization of InGaAsN/GaAs Quantum-well Ridge Laser Diodes for High Frequency Operation

Optimization and characterization of multiple InGaAsN/GaAs quantum-well laser diodes for high frequency operation are reported. From the modelling of the dilute nitride quantum well, we investigate how to design the structure to achieve a high frequency operation. The gain characteristics are optimized by incorporating the minimum amount of nitrogen in the well to obtain the emission at 1.3 μm with a low transparency density and a high differential gain. We show that the number of wells must be adjusted to three to benefit of the best compromise between the threshold current and the differential gain. The effects of the cavity losses on the dynamic characteristics are evaluated and demonstrate the interest for high cavity losses to reach high relaxation frequency despite a lower characteristic temperature. An optimized structure has been realized and exhibits an emission at 1.34 μm with a transparency current density of 642 A/cm² and a characteristic temperature T₀ ~ 80 K. Dynamic properties for ridge devices are evaluated from relative intensity noise measurements and small-signal modulation. A relaxation frequency as high as 7.4 GHz and a 9.7 GHz small-signal bandwidth are reported. We demonstrate transmission up to 10 Gb/s at 25°C without penalty and bit error floor.     

GaInAsSb/AlGaAsSb lasers in the wavelength range between 2.73 μm and 2.93 μm

Compressively strained multiple quantum well lasers in the GaInAsSb/AlGaAsSb material system are reported. Indium concentrations between 40% and 47.5% were chosen for the GaInAsSb quantum wells. Compressive strains varied between 1.16% and 1.43%. The lasers worked continuous wave at room temperature up to a wavelength of 2.81 μm. For a laser with 2.93 μm wavelength continuous wave operation was found up to a temperature of −23°C. This laser worked in pulsed operation at 15°C.     

Numerical analysis of InGaAs–InP multiple-quantum well laser emitting at 2 {\upmu }m

Multiple-quantum well InGaAs laser structures emitting at 2  \(\upmu \) m with different barriers are modeled using commercial software that combines gain calculation with 2-D simulations of carrier transport and waveguiding. The model is calibrated using experimental results. The simulated results show a non-uniform distribution of carriers in different quantum wells with InGaAlAs barriers which affects their contribution to the gain. The carrier uniformity and a reduction in threshold current density are observed when we use an InGaAs barrier material. The quantum well number was varied from 2 to 4 in both structures and a comparison of the threshold current and its variation with temperature were investigated.     

Influence of Nonlinear Gain Saturation on the Time-Bandwidth Product of Optical Pulse from a Gain-Switched Semiconductor Laser

It is found numerically that the time-bandwidth product (TBP) of optical pulse from a gain-switched semiconductor laser operating under a sufficient gain saturation condition increases monotonously with increasing modulation amplitude. This enhancement of the TBP becomes remarkable for longer-wavelength semiconductor lasers (1.3, 1.55 μm) having large value of the gain compression factor ε (∼ 10⁻²³ m³), making the pulse chirp estimation using the TBP difficult.     

Simulation of a Single-Mode Tunnel-Junction-Based Long-Wavelength VCSEL

We investigate the physics of an internal device for a high-performance, vertical-cavity surface-emitting laser operating at 1.305 μm. Experimental results are analyzed using as the simulation software a photonic-integrated-circuit simulator in 3D (PICS3D), which is a state-of-the-art 3D simulator for surface- and edge-emitting laser diodes, semiconductor optical amplifiers, and other similar active waveguide devices. The 2D/3D semiconductor equations are coupled to the optical modes in both lateral and longitudinal directions. Optical properties such as the quantum well/wire/dot optical gain and spontaneous emission rates are computed self-consistently. Careful adjustments of material parameters led to an excellent agreement between simulation and measurements. Simulation results show that the maximum output power is limited by electron leakage from quantum wells.     

Generation of optical waveforms in 1.3-μm SOA-based fiber lasers

Passive optical waveform generation is obtained in fiber lasers using a 1.3-μm semiconductor optical amplifier (SOA) as the gain medium. Various waveforms, including square wave, staircase wave, triangular wave, pulse, and dark pulse are generated in SOA-based fiber lasers by adjusting intracavity polarization controllers. The passive waveform generation might be attributed to the SOA gain dynamics and the enhanced nonlinear interaction at the 1.3-μm zero dispersion wavelength of traditional single-mode fiber (SMF), as well as the interference effect between the two sub-cavities of fiber laser. With figure-8 cavity configuration, 1250th-order harmonic pulses have been successfully demonstrated. We have also obtained a free-running SOA-based fiber laser with 3-dB spectral width of 16 nm, and the center wavelength can be tuned over 45 nm range.     

Near-field magneto-photoluminescence of quantum-dot-like composition fluctuations in GaAsN and InGaAsN alloys

Near-field magneto-photoluminescence scanning microscopy has been used to investigate the structural and optical properties of quantum-dot (QD)-like compositional fluctuations in GaAsN and InGaAsN alloys. Sharp spectral lines (halfwidth 0.5–2 meV) from these QDs are observed at T<70 K, and their Zeeman splitting and diamagnetic shifts are used to determine the size (r6–18 nm), density (100 μm⁻³), and nitrogen composition. Near-field scanning images reveal phase separation effects in the distribution of nitrogen, but little effect appears from the presence or absence of indium. Indium does have a strong effect on the exciton g-factor for observations in a magnetic field.     

InGaAsP/GaAs SCH SQW laser arrays grown by LPE

InGaAsP/InGaP/GaAs separate confinement heterostructure (SCH) single quantum well (SQW) laser structures have been obtained by an improved liquid-phase epitaxy (LPE) process. Wide-contact stripe lasers have been fabricated with threshold current density below 300 A/cm² and cavity length of 800 μm. Finally, with the same grown wafers, 1-cm bar laser diode (LD) arrays are made with 150 μm wide stripes and a maximum fill factor of 30%. Continuous Wave (CW) power output of 20 W has been reached.     

Strain interactions and defect formation in stacked InGaAs quantum dot and dot-in-well structures

The growth of high-quality stacked quantum dot (QD) structures represents one of the key challenges for future device applications. Electronic coupling between QDs requires closely separated electronic levels and thin barrier layers, requiring near identical composition and shape, despite strong strain interactions. This paper presents a detailed characterization study of stacked InGaAs QD and InAs/InGaAs dot-in-well (DWELL) structures using cross-sectional transmission electron microscopy. For In_.5Ga_.5As/GaAs QD structures we have observed optimized stacking using a barrier thickness 12 nm.We also report studies of stacking in DWELL laser structures. Despite reports of very low threshold currents in such lasers, designed for 1.3 μm emission, performance is limited by gain saturation and thermal excitation effects. We have explored solutions to these problems by stacking multiple DWELL layers of three, five and 10 repeats. Initial attempts at stacked multilayer structures, particularly samples with a large number of repeats, produced variable results, with a number of the final devices characterized by poor emission and electrical characteristics. Analysis by transmission electron microscopy has identified the presence of large defective regions arising from the complex interaction of dots on several planes and propagating threading dislocations into the cladding layers. The origin of this defect is identified as the coalescence of QDs at very high density and the resulting dislocation propagating to higher dot planes. An effective modified method to reduce the defect density by growing the barrier layer at higher temperature will be discussed. Finally, we report the growth of a stacked 10-layer structure using relatively thin barriers, grown using this technique.     

GaAsN/GaAs量子阱在1 MeV电子束辐照下的退化规律

为研究GaAsN/GaAs量子阱在电子束辐照下的退化规律与机制,对GaAsN/GaAs量子阱进行了不同注量(1×1015,1×1016 e/cm2)1 MeV电子束辐照和辐照后不同温度退火(650,750,850℃)试验,并结合Mulassis仿真和GaAs能带模型图对其分析讨论。结果表明,随着电子注量的增加,GaAsN/GaAs量子阱光学性能急剧降低,注量为1×1015 e/cm2和1×1016 e/cm2的电子束辐照后,GaAsN/GaAs量子阱PL强度分别衰减为初始值的85%和29%。GaAsN/GaAs量子阱电子辐照后650℃退火5 min,样品PL强度恢复到初始值,材料带隙没有发生变化。GaAsN/GaAs量子阱辐照后750℃和850℃各退火5 min后,样品PL强度随退火温度的升高不断减小,同时N原子外扩散使得样品带隙发生约4 nm蓝移。退火温度升高没有造成带隙更大的蓝移,这是由于进一步的温度升高产生了新的N—As间隙缺陷,抑制了N原子外扩散,同时导致GaAsN/GaAs量子阱光学性能退化。     

Bit-rate Flexible Picosecond Pulse Width Conversion with All-optical Mono-stable Multivibrator Laser Diode

An optical mono-stable multivibrator laser diode (MM-LD) is realized by using a multi-electrode distributed feedback laser diode. All-optical pulse-width conversion of ultra-short pulses to non-return-to-zero (NRZ) is achieved using an MM-LD. The MM-LD is adopted for a wide range of bit-rates between 2-10 Gbit/s by tuning the DC bias. Data format transformation from 10-Gbit/s return-to-zero optical signals to NRZ optical-signals is achieved with error free operation. Converted optical signals, which have a narrower spectral bandwidth and lower peak power than when input, are transmitted using a 1.3-μm zero dispersion fiber (1.3Aλ₀-SMF).     

Picosecond timescale carrier dynamics of InAs quantum dots: The role of a continuum background

We have investigated the ultrafast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots emitting at 1.3 μm by means of time resolved photoluminescence upconversion measurements with a time resolution of about 200 fs. The detection energies scan the spectral region from the energy of the quantum dot excitonic transition up to the barrier layer absorption edge. We found, under high excitation intensity, that the intrinsic electronic states are populated mainly by carriers directly captured from the barrier.