MQW Lasers Research Articles

III/V-on-Si MQW lasers by using a novel photonic integration method of regrowth on a bonding template

Silicon photonics is becoming a mainstream data-transmission solution for next-generation data centers, high-performance computers, and many emerging applications. The inefficiency of light emission in silicon still requires the integration of a III/V laser chip or optical gain materials onto a silicon substrate. A number of integration approaches, including flip-chip bonding, molecule or polymer wafer bonding, and monolithic III/V epitaxy, have been extensively explored in the past decade. Here, we demonstrate a novel photonic integration method of epitaxial regrowth of III/V on a III/V-on-SOI bonding template to realize heterogeneous lasers on silicon. This method decouples the correlated root causes, i.e., lattice, thermal, and domain mismatches, which are all responsible for a large number of detrimental dislocations in the heteroepitaxy process. The grown multi-quantum well vertical p–i–n diode laser structure shows a significantly low dislocation density of 9.5 × 104 cm−2, two orders of magnitude lower than the state-of-the-art conventional monolithic growth on Si. This low dislocation density would eliminate defect-induced laser lifetime concerns for practical applications. The fabricated lasers show room-temperature pulsed and continuous-wave lasing at 1.31 μm, with a minimal threshold current density of 813 A/cm2. This generic concept can be applied to other material systems to provide higher integration density, more functionalities and lower total cost for photonics as well as microelectronics, MEMS, and many other applications.

The Optical Gain of a Si-Based Lattice-Matched Si0.15Ge0.621Sn0.229/Si0.637Ge0.018Sn0.345 MQW Laser

We study the optical-gain characteristics of a Si-based MQW laser, in which the active region has 20 Si0.15Ge0.621Sn0.229 quantum wells separated by 20 Si0.637Ge0.018Sn0.345 barriers. We reach a maximum optical gain of 2300 cm−1 with an estimated carrier concentration of 5·1018 cm−3, which is equivalent to the transparent current density equal to 0.5 kA/cm2. Furthermore, we discuss the optical confinement factor and modal gain. The modal gain depends sensitively on the number of the quantum wells (QWs), and this fact restricts the optical confinement factor. The modal gain of the model we proposed can reach 1500 cm−1 at the injection current density equal to 3 kA/cm2. We hope that our results show the possibility to obtain a Si-based near-infrared laser.

Influence of Chirp of High-Speed Laser Diodes and Fiber Dispersion on Performance of Non-Amplified 40-Gbps Optical Fiber Links

Abstract — We model and simulate the combined effect of fiberdispersion and frequency chirp of a directly modulated high-speedlaser diode on the figures of merit of a non-amplified 40-Gbps opticalfiber link. We consider both the return to zero (RZ) and non-return tozero (NRZ) patterns of the pseudorandom modulation bits. Theperformance of the fiber communication system is assessed by thefiber-length limitation due to the fiber dispersion. We study theinfluence of replacing standard single-mode fibers by non-zerodispersion-shifted fibers on the maximum fiber length and evaluatethe associated power penalty. We introduce new dispersiontolerances for 1-dB power penalty of the RZ and NRZ 40-Gbpsoptical fiber links. Keywords — Bit error rate, dispersion, frequency chirp, fibercommunications, semiconductor laser. I. I NTRODUCTION N the current information age, there is a steady need toincrease the capacity of information transmitted to orexchanged among users, especially over optical fibers.Modern cost-effective and broadband fiber networks, such asthe fiber-to-the-home (FTTH) and radio over fiber (RoF),require directly modulated laser diodes with bandwidthexceeding 25 GHz for operating the fiber links withtransmission speeds exceeding 40 Gbps [1]. Due to theinferior characteristics in the transient regime of thesemiconductor laser, its resonance and modulation bandwidthare limited to values more or less than 10 GHz. One typicalsolution to increase the modulation bandwidth is to increasethe differential gain of the laser diode [2], [3]. This property isa typical advantage of the MQW laser diodes [4]. Sato et al.[3] demonstrated a MQW-DFB laser emitting at thewavelength of 1.55 m to meet the requirement of 40 Gbpsfiber transmission systems for use in very-short-reach fiberlinks and metro area networks [5].The intensity modulation of high-speed semiconductorlasers, however, is coupled to the phase variation through thelinewidth enhancement factor [6], [7] which then induces atime variation in the lasing frequency, referred to as“frequency chirp” [8]. This frequency chirp is proportional tothe differential gain and, therefore, attains large in high-speed

InP-based Sb-free Lasers and Photodetectors in 2-3 μm Band

Zhang et al. efforts on the explore of InP-based Sb-free 2-3 μm band lasers and photodetectors are introduced, including the 2-2.5 μm band type I InGaAs MQW lasers under pseudomorphic triangle well scheme, 2.5-3.0 μm band type I InAs MQW lasers under metamorphic strain compensated well scheme, as well as InGaAs photodetectors of high indium contents with cut-off wavelength large than 1.7 μm. All device structures are grown using gas source MBE method, and CW operation above room temperature have been reached for the lasers with wavelength less than 2.5 μm. Pulse operation of 2.9 μm lasers at TE temperature also have been reached The dark current of 2.6 μm InGaAs photodetectors have been decreased notably with the inserting of supperlattice electron barriers, those types of epitaxial materials have been used to the development of FPA modules for space remote sensing applications.

Simple technique for evaluating dimensional and compositional changes in selective-area-grown MQW laser diode.

We report on a novel combination of measurement techniques for evaluating dimensional and compositional changes of selective-area-grown multiple-quantum-well laser diodes (SAG MQW LDs). This technique is based on C-V and I-V measurements of the fully fabricated LDs. Using this technique, the changes in the capacitance and voltage correspond to the layer thickness and bandgap energy. To verify the effectiveness of the proposed technique, we first fabricated an LD array containing ten different SAG MQW structures, and examined the effects of the dimensional and compositional changes on the wavelength shift both theoretically and experimentally. From our examination, we found that a wavelength shift of 83 nm is obtained for an SAG mask pattern with an opening width of 100 μm, and that a cross point between both dimensional and compositional changes exists for this mask pattern. As the following step, the fabricated LD array was tested using the proposed technique, and the growth rate enhancement and bandgap energy were extracted from the measured C-V and I-V results. The extracted data for each array channel were compared with the simulation results, which were well-fitted from the photo-luminescence (PL) measurements. They both show good agreement with the simulation results.

DC Characterizations of MQW Tunnel Diode and Laser Diode Hybrid Integration Device

A multiple quantum well tunnel diode (TD) and laser diode (LD) hybrid integration device (TD-LD) was fabricated. Additional current supply was applied to adjust the LD's operating point. DC characteristics were investigated in both voltage source and current source drive circuits at room temperature. Different results from the two drive circuits are discussed.

Influence of Magnetic Field on the Threshold Current, Temperature Characteristics, and on the Output Power in AlGaInP Multiple Quantum Well Laser

In this paper we report the effects of relatively weak magnetic fields (up to 2T) on the threshold current, temperature characteristics and output power of AlGaInP MQW laser. The threshold current and temperature characteristics increased while the output power decreased by applying the magnetic field at different directions with respect to the quantum well plane. This paper presents a new insight into the mechanism that influence changes in the properties of MQW laser on application of magnetic fields based on the dynamics of electron-hole recombination.

Linear increase of the modal gain in1.3 µm InAs/GaAs quantum dot lasers containing up to seven-stacked QD layers

The authors have recently demonstrated the enhancement of the quantumdot laser modal gain, linearly scaling with the number of stacked QD layers.These results allowed the achievement of multi-quantum dot (MQD) lasers, thezero-dimensional counterpart of MQW lasers, with a modal gain as high as42 cm−1, in a seven-layer structure. A detailed investigation of the structural and optical propertieswas performed on laser structures with three, five and seven QD layers. Such aninvestigation clearly shows that the high uniformity of QD layer features is responsible forthe linear increase of the modal gain and its high value.

Cathodoluminescence study of GaN-based film structures

GaN films grown on sapphire substrate with an emphasis on epitaxial lateral overgrown (ELOG) layers with an array of rhombic shaped mask area as well as InGaN/GaN MQW laser diode layer structures were investigated by cathodoluminescence (CL) spectroscopy and CL imaging at room and low temperatures. The microscopic imaging with a high-spatial resolution clearly reveals the distribution of threading dislocations and point defects in ELOG GaN films. The secondary electron and CL data measured on cleaved faces of laser diodes are analyzed in consideration with luminescence mechanisms in semiconductor heterostructures and around the p - n junction, providing important information on the defects and carrier dynamics in laser diode devices.

Optical-field profiles in In xGa 1− xN -MQW laser structures

In this paper, we calculated the optical fields for In x Ga 1− x N-multiquantum well (MQW) laser structures. Two different optical cavities are compared, the conventional step separate confinement heterostructure (Step) and a graded-index (GRIN) structure with a parabolic variation of the Al content in the Al x Ga 1− x N guide layers. A comparison is made regarding the confinement factor, near- and far-field patterns. An anomalous behavior for the confinement factor is observed in the structure, and it can be eliminated by choosing an appropriated combination of the layer’s thicknesses forming the waveguide. For Al x Ga 1− x N, an improved expression for the refractive index is presented, which shows better agreement with experimental data than previously reported expressions.

Blue‐shift of phosphorous‐implanted InGaAs/InGaAsP MQW laser structures by two‐step anneals

We describe studies of implantation-enhanced quantum-well intermixing in a lattice-matched InGaAs/InGaAsP multiple quantum well p-i-n heterostructure. Samples were implanted with a dose of 5×1014 P+ ions /cm2 at high energy of 1 MeV. The band gap for the samples was determined from photoluminescence at room temperature. The maximum blue-shift of the band gap was 107 nm after the RTA process at 675 °C for 9 minutes. However, it was improved to 140 nm after two-step anneals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of InGaAlAs MQW buried heterostructure lasers by narrow stripe selective MOVPE

Fabrication of InGaAlAs MQW buried heterostructure (BH) lasers by narrow stripe selective MOVPE is demonstrated in this paper. High quality InGaAlAs MQWs were first grown by narrow stripe selective MOVPE without any etching process and assessed by analysing the cross sections and PL spectrums of the InGaAlAs MQWs. Furthermore, BHs were fabricated for the InGaAlAs MQW lasers by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good device characteristics, with a high internal differential quantum efficiency of 85% and a low internal loss of 6.7 cm−1. Meanwhile, narrow divergence angles of the far field pattern are obtained for the fabricated lasers.

Monolithic 40-GHz Mode-Locked MQW DBR Lasers for High-Speed Optical Communication Systems

The state-of-the-art of the development and fabrication of advanced 1.55-mum/40-GHz pulse laser modules with a monolithic InP-based mode-locked distributed Bragg reflector (DBR) MQW laser chip inside is reported, with respect to the future applications in high-speed optical communications. We emphasize the latest improvements for hybrid mode-locked devices, which integrate a saturable absorber or an electroabsorption modulator. We further illustrate different technical approaches that enable meeting predetermined frequencies and wavelengths, and which are at the same time promising with respect to high fabrication yields

Continuous Wave Performance and Tunability of MBE Grown2.1 μm InGaAsSb/AlGaAsSb MQW lasers

InGaAsSb/AlGaAsSb multi quantum well ridge waveguide lasers at2.1 μm wavelength are fabricated by using molecular beam epitaxy.Continuous wave performance and tunability of the lasers are evaluatedin a wide temperature range extend to 80°C. Output power of the laserat 30°C exceeds 30 mW/facet at driving current of 0.5 A, thecharacteristic temperature T0 is 89 K in 0–50°C range. Nofast degradation is observed in accelerated aging test at 90°C forthose lasers with lower Al content in cladding layers. Temperaturetunability of the lasers is 1.36 nm/K. Single-mode output with side modesuppression ratios greater than 20 dB is achieved in a certaindriving current region; current tunability is 8×10−3 nm/mAregardless of mode hopping.

A numerical study of characteristic temperature of short-cavity 1.3-μm AlGaInAs/InP MQW lasers

Optical properties of a 1.3-μm AlGaInAs/InP strained multiple quantum-well structure with an AlInAs electron stopper layer, which is located between the active region and the p-type graded-index separate confinement heterostructure layer, are studied numerically with a LASTIP simulation program. Specifically, the effect of the electron stopper layer on the characteristic temperature and the temperature dependence of the slope efficiency are investigated. Various physical parameters at different operating temperatures are adjusted so that the threshold currents of the simulated laser structure can be matched to the experimental results of an identical laser structure fabricated by Selmic et al. The simulation results suggest that, with the use of a p-type Al0.5In0.5As electron stopper layer and a strain-compensated active region consisting of Al0.175Ga0.095In0.73As (6 nm)/Al0.32Ga0.2In0.48As (10 nm), a characteristic temperature as high as 108.7 K can be achieved for a 250-μm-long AlGaInAs/InP laser.

Confinement factor, near and far field patterns in InGaN MQW laser diodes

AbstractIn this work the influence of the QW number in the active region on spectral characteristics in InGaN multi quamtun well lasers is analyzed. A comparison between the abrupt index step structure (Step) and a graded‐index structure (GRIN) is done. The effect of the introduction of a p‐AlxGa1–xN electron blocking layer, placed above the last InGaN barrier in the Step structure is also analyzed. Calculations of the confinement factor, near and far field patterns were carried out. We found that with the adequate aluminum content in this layer, the confinement factor, near and far field patterns are improved, and values similar to those obtained with GRIN structure can be reached. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison of thermal characteristics of antimonide and phosphide MQW lasers

The thermal characteristics of antimonide ridge waveguide MQW lasers have been investigated numerically and experimentally, and compared with phosphide lasers in detail. Using the finite-element method, the heat accumulation and dissipation process of the lasers under CW and pulse driving conditions have been simulated, and quantitative thermal time constants were introduced to describe the cooling efficiency of the lasers. The non-uniform temperature distribution inside the active core of the laser and its effects on lasing spectra have been discussed, and confirmed by the measurement of the broadening of the lasing spectrum towards the blue side. A way to improve the thermal property of antimonide lasers have also been proposed and discussed.

Outcome of refinement of the thermal sensitivity Ga 0.65 In 0.35 As 0.15 Sb 0.85 /GaSb MQW laser

We discuss an optimization procedure for type-II mid-IR lasers. The QW layer composition was used as the variable parameter. The proposed design combines the suppression of the Auger recombination processes and the improvement of the electron and hole confinement, the characteristic temperature T0 of the strained Ga1–xInxAsySb1–y/GaSb MQW laser during laser operation in the 250–350 K temperature range. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison between a graded and step-index optical cavity in InGaN MQW laser diodes

In this paper we theoretically analysed the influence of the number of QWs in the active region and the cladding layer width on the confinement factor, near field patterns and far field patterns. A comparison between the conventional step separate confinement heterostructure (SCH) and a graded-index separate structure (GRIN-SCH) is done regarding these parameters. We found that in the case of single quantum well structure the step cavity gives the highest values of the confinement factor. As the number of wells (N) in the active region is increased the superiority of one structure or the other depends on the cladding layer width and the value of N, but for values of N higher than six, the confinement factor is always higher in the structure with a GRIN cavity, independent of the cladding layer width. In general the far field patterns in GRIN structure have lower values of the full width half-maximum (FWHM). The cutoff condition for a mono mode optical cavity is also calculated in both structures.

Heat management of MBE-grown antimonide lasers

The heat management of the AlGaAsSb/InGaAsSb ridge waveguide MQW laser at 2 μm wavelength range has been investigated by using the finite-element method (FEM). Results show that the thermal behavior of antimonide lasers is quite different from InP or GaAs-based lasers mainly due to the low thermal conductivities of antimonides, which are coincident with the observed results. By using junction down-mounting or using thick gold plating layer as heat spreader on the top contact for substrate down-mounting, the thermal characteristics of the antimonide lasers can be dramatically improved.