Quantum Well Lasers Research Articles

Impact of modal gain and waveguide design on two-state lasing in quantum well-dot lasers.

We study the current-controlled lasing switching from the ground state (GS) to the excited state (ES) transition in broad-area (stripe width 100 µm) InGaAs/GaAs quantum well-dot (QWD) and quantum well (QW) lasers. In the lasers with one QWD layer and a 0.45 µm-thick GaAs waveguide, pure GS lasing takes place up to an injection current as high as 8 A (40 kA/cm2). In contrast, in QW lasers with a similar design, ES lasing emerges already at 3 A (15 kA/cm2). The ES lasing in the QWD lasers is observed only in the devices with a waveguide thickness of 0.78 µm that supports a 2nd order transverse mode at the wavelength of the ES transition. Increasing the modal gain in the lasers with 0.78 µm-thick waveguide by using two QWD layers in the active region suppresses the ES lasing.

Optical gain and related proerties of GaSbN/GaSb quantum-well laser: numerical approach

Currently, lasers are still of ongoing interest. They are used in a large range of practical applications in our day life and across various fields. Utilizations include industry such as in cutting, welding, drilling, and engraving of various materials, in medicine such as in surgery for precise cutting and cauterization with minimal tissue damage, in ophthalmology, dentistry for removing tooth decay and reshaping dental tissues, in high-speed data transmission through optical fibers, in science and research (spectroscopy, metrology and holography) and for creating visual displays, etc. The optical gain of a laser diode is a key characteristric that exhibits the performances of lasers. In the present work, we investigated the optical gain of a strained GaSbN/GaSb quantum well laser with nitrogen concentration of 3%. This low nitrogen concentration makes our GaSbN alloy a dilute one. Our analysis focused on the impact of carrier density and quantum well width on optical gain of the laser device being studied. Additionally, we determined the relationship between quantum well width and emitted wavelength. Our numerical results indicate an effective correlation between optical gain and both carrier density and quantum well width. Furthermore, inasing the quantum well width led to a longer emitted wavelength. The laser demonstrated emission within the infrared-red spectrum.

Investigating the mechanism of enhancing interfacial adhesion of SiOx films on GaAs substrates through process optimization

In the manufacturing of GaAs-based quantum well (QW) lasers, the adhesion between the Silicon dioxide (SiOx) film layer and the Gallium arsenide (GaAs) substrate is crucial for the performance and durability of semiconductor devices. This study focused on depositing SiOx films on GaAs substrates using plasma-enhanced chemical vapor deposition (PECVD). The research aimed to investigate the impact of different coating processes on the deposition rate, properties, and composition of the coatings. The interfacial adhesion of various samples was assessed using nano-scratch tests. The results revealed that samples with lower SiH4 gas flow and RF power, or higher process pressure exhibited stronger adhesion strength. It's further observed that optimizing the process parameters reduced residual stresses in the film, thereby enhancing the GaAs-SiOx interfacial bonding. This work has the potential to significantly reduce the possibility of QW lasers malfunctions, improve the reliability of semiconductor devices and provide valuable insights for future studies on enhancing film-substrate adhesion.

Silicon‐Based 850 nm GaAs/GaAsP‐Strained Quantum Well Lasers with Active Region Dislocation Blocking Layers

A silicon‐based room temperature (RT) continuous wave (CW) operation quantum well (QW) laser emitting at 850 nm is reported in this article. By applying the dislocation filter superlattice, the threading dislocation density of the GaAs pseudosubstrate on Si is reduced to 1.8 × 107 cm−2. The metal‐organic chemical vapor deposition‐grown laser structure with GaAs/GaAsP QW and InAlAs active region dislocation blocking layer are fabricated into broad‐stripe Fabry–Perot laser diodes. A typical threshold current and threshold current density of 286 mA and 715 Acm−2 are obtained with 2 mm cavity length and 20 um stripe width samples. A 94.2 mW single‐facet output power lasing around 854 nm and a 0.314 WA−1 slope efficiency is measured under RT CW operation. After a 10‐min aging process, the tested laser can operate stably under continuous operation conditions at RT and the lifetime can be approximated using an exponential fitting curve, indicating a good life reliability of this QW laser.

Turnkey locking of quantum-dot lasers directly grown on Si

Ultralow-noise laser sources are crucial for a variety of applications, including microwave synthesizers, optical gyroscopes and the manipulation of quantum systems. Silicon photonics has emerged as a promising solution for high-coherence applications due to its ability to reduce the system size, weight, power consumption and cost. Semiconductor lasers based on self-injection locking have achieved fibre laser coherence, but typically require a high-quality-factor external cavity to suppress coherence collapse through frequency-selective feedback. Lasers based on external-cavity locking are a low-cost and turnkey operation option, but their coherence is generally inferior to self-injection locking lasers. In this work, we demonstrate quantum-dot lasers grown directly on Si that achieve self-injection-locking laser coherence under turnkey external-cavity locking. The high-performance quantum-dot laser offers a scalable and low-cost heteroepitaxial integration platform. Moreover, the chaos-free nature of the quantum-dot laser enables a 16 Hz Lorentzian linewidth under external-cavity locking using a low-quality-factor external cavity, and improves the frequency noise by an additional order of magnitude compared with conventional quantum-well lasers.

Comparison of quantum well structures for room temperature continuous wave 980 nm lasers grown on (001) Si by MOCVD

We report room temperature (RT) continuous-wave (CW) lasing of quantum well (QW) lasers grown on (001) Si substrates emitting at 980 nm. Two different QW structures, including conventional compressively strained InGaAs/GaAs QWs and strain-compensated InGaAs/GaAs/GaAsP QWs, were investigated. Photoluminescence properties and device performance of both structures on native GaAs and (001) Si substrates are discussed. By adding GaAsP barriers to the InGaAs/GaAs QWs, the lowest threshold current density of ridge waveguide edge-emitting QW lasers obtained on Si is 550 A/cm2, measured on a 10 μm × 2 mm device at RT. The working temperature of the InGaAs/GaAs/GaAsP QW lasers grown on Si can be over 95 °C in the CW mode. This work suggests a feasible approach to improve the 980 nm laser performance on Si for monolithic optoelectronic integration.

III–V semiconductor devices grown by metalorganic chemical vapor deposition—The development of the Swiss Army Knife for semiconductor epitaxial growth

Metalorganic chemical vapor deposition (MOCVD) epitaxial materials technology for the growth of compound semiconductors has been developed over the past 60-plus years to become the dominant process for both research and production of light-emitting devices as well as many other electronic and optoelectronic devices. Today, MOCVD has become the “Swiss Army Knife” of semiconductor epitaxial growth, covering a wide variety of compound semiconductors and device applications. Because of the flexibility and control offered by this process and the material quality produced by MOCVD, many important III–V semiconductor devices have become commercially viable. This paper attempts to provide a personal view of the early development of MOCVD and some brief historical discussion of this important and highly versatile materials technology for the growth of high-quality devices employing ultrathin layers and heterojunctions of III–V compound semiconductors, e.g., quantum-well lasers, light-emitting diodes, heterojunction solar cells, transistors, and photonic integrated circuits.

Quantifying non-threshold Auger-recombination processes in mid-wavelength infrared range HgCdTe quantum wells

We study photoluminescence temperature quenching in HgTe/CdHgTe quantum wells (QWs) emitting at 3–4 μm wavelengths and recover temperature-dependent interband recombination rates. Recombination coefficients are determined for the process that we identify as a non-threshold ehh Auger process involving valence band continuum states in barriers. With the effective Auger coefficient CA reaching ∼10−13 cm4/s under resonant conditions, such a process is shown to determine stimulated emission thresholds in a wide temperature interval, while the contribution of conventional, activated Auger processes is presumably rather limited. Thus, threshold energy considerations should be used with caution for the optimization of HgCdTe QW lasers operating around 3 μm, and relatively low-barrier QWs may provide better performance than the high-barrier ones despite lower energy thresholds for thermally activated eeh-Auger recombination. It holds as long as the conduction band offset is detuned from the bandgap energy to avoid additional non-threshold eeh-processes and sufficient hole localization at elevated temperatures is maintained.

Reliability enhancement of InGaAs/AlGaAs quantum-well lasers on on-axis Si (001) substrate

The enhancement of the reliability of the silicon-based III–V quantum well lasers, especially of those on an on-axis Si (001) substrate, is of great importance now a days for the development of Si-based photonic and even optoelectronic integrated circuits and is really quite challenging. As an experimental advancement, mainly by inserting a pair of InAlAs strained layers separately into the upper and lower AlGaAs cladding layers to effectively prevent the formation of the in-plane gliding misfit-dislocations within the boundary planes of the active region, the longest room-temperature and continuous-wave lifetime of the InGaAs/AlGaAs quantum well lasers on an on-axis Si (001) substrate with a cavity length of 1500 µm and a ridge width of 20 µm has been prolonged from a very initial record of ∼90 s to the present length longer than 31 min. While, the highest continuous-wave operation temperature of another one with a cavity length of 1000 µm and a ridge width of 10 µm has been shown as 103 °C with an extracted characteristic temperature of 152.7 K, further enhancement of the device reliability is still expected and would mainly depend on the level of the threading-dislocation-density reduction in the GaAs/Si virtual substrate.

Linewidth enhancement factor of type-II red InGaN/GaNSb/GaN quantum-well lasers

We investigate the linewidth enhancement factor of the type-II red InGaN/GaNSb/GaN quantum-well (QW) laser, employing a non-Markovian gain model with many-body effects included. It is shown that the linewidth enhancement factor of the type-II red InGaN/GaNSb/GaN QW structure is almost independent of the peak-gain coefficient. This behavior is contrasted with that of the conventional type-I InGaN/GaN QW structure, whose linewidth enhancement factor increases as the peak-gain coefficient increases. These results can be explained by the peak-gain dependencies of the differential refractive-index change and the differential gain. Moreover, the type-II red InGaN/GaNSb/GaN QW laser yields much smaller values of the linewidth enhancement factor than the conventional type-I InGaN/GaN QW laser. The type-II red InGaN/GaNSb/GaN QW laser with a relatively small, excitation-independent linewidth enhancement factor is expected to be highly useful for many practical applications.

InP/InGaAs/AlGaAs quantum-well semiconductor laser with an InP based 1550 nm n-GaAsSb single waveguide structure

InP/InGaAs/AlGaAs quantum-well semiconductor laser with an InP based 1550 nm n-GaAsSb single waveguide structure

Influence of carrier transport on modulation characteristics of quantum-well semiconductor lasers

Influence of carrier transport on modulation characteristics of quantum-well semiconductor lasers

Linewidth narrowing in self-injection-locked on-chip lasers

Stable laser emission with narrow linewidth is of critical importance in many applications, including coherent communications, LIDAR, and remote sensing. In this work, the physics underlying spectral narrowing of self-injection-locked on-chip lasers to Hz-level lasing linewidth is investigated using a composite-cavity structure. Heterogeneously integrated III–V/SiN lasers operating with quantum-dot and quantum-well active regions are analyzed with a focus on the effects of carrier quantum confinement. The intrinsic differences are associated with gain saturation and carrier-induced refractive index, which are directly connected with 0- and 2-dimensional carrier densities of states. Results from parametric studies are presented for tradeoffs involved with tailoring the linewidth, output power, and injection current for different device configurations. Though both quantum-well and quantum-dot devices show similar linewidth-narrowing capabilities, the former emits at a higher optical power in the self-injection-locked state, while the latter is more energy-efficient. Lastly, a multi-objective optimization analysis is provided to optimize the operation and design parameters. For the quantum-well laser, minimizing the number of quantum-well layers is found to decrease the threshold current without significantly reducing the output power. For the quantum-dot laser, increasing the quantum-dot layers or density in each layer increases the output power without significantly increasing the threshold current. These findings serve to guide more detailed parametric studies to produce timely results for engineering design.

980 nm electrically pumped continuous lasing of QW lasers grown on silicon.

Investigation of high-performance lasers monolithically grown on silicon (Si) could promote the development of silicon photonics in regimes other than the 1.3 -1.5 µm band. 980 nm laser, a widely used pumping source for erbium-doped fiber amplifier (EDFA) in the optical fiber communication system, can be used as a demonstration for shorter wavelength lasers. Here, we report continuous wave (CW) lasing of 980 nm electrically pumped quantum well (QW) lasers directly grown on Si by metalorganic chemical vapor deposition (MOCVD). Utilizing the strain compensated InGaAs/GaAs/GaAsP QW structure as the active medium, the lowest threshold current obtained from the lasers on Si was 40 mA, and the highest total output power was near 100 mW. A statistical comparison of lasers grown on native GaAs and Si substrates was conducted and it reveals a somewhat higher threshold for devices on Si. Internal parameters, including modal gain and optical loss are extracted from experimental results and the variation on different substrates could provide a direction to further laser optimization through further improvement of the GaAs/Si templates and QW design. These results demonstrate a promising step towards optoelectronic integration of QW lasers on Si.

Directly-coupled well-wire hybrid quantum confinement lasers with the enhanced high temperature performance

It is well known that the laser diode performance will inevitably deteriorate when the device is heated. It has been a difficult issue to solve to date. In this letter, we are reporting a new solution to improve high-temperature performance of the laser diodes. The device uses a kind of directly-coupled well-wire hybrid quantum confinement (HQC) structure of the active medium based on the InGaAs–GaAs–GaAsP material system. This special HQC structure is constructed based on the strain-driven indium (In)-segregation effect and the growth orientation-dependent on-GaAs multi-atomic step effect. The measurement and analysis for the HQC laser sample show that the carrier leakage loss, the Auger recombination and gain-peak shifting due to heating are reduced in the HQC structure. It therefore increases the optical gain for lasing at high temperature. The power conversion efficiency is enhanced by >57% and the threshold carrier density drops by >24% at T ⩾ 360 K, in comparison to the traditional quantum-well laser performance. A higher characteristic temperature of 240 K is obtained as well. It implies the better thermal stability of the HQC laser structure. These achievements show a significant prospect for developing high thermo-optic performance of laser diodes.

Spontaneous mode locking of a multimode semiconductor laser under continuous wave operation

Self-starting mode-locking is observed in a laser based on a compact III-V diode-pumped quantum-well surface-emitting semiconductor laser technology with a saturable-absorber-free but dispersive cavity. Continuous wave generation of picosecond pulses at a rate of 100 GHz is demonstrated by recording microwave intensity noises, beat frequency, time-resolved optical spectra, and intensity autocorrelation. Coherence of the pulse train is obtained through the frequency noise measurement of the demodulated beat note, demonstrating a timing jitter as low as 110 fs, near the quantum limit. Using a theoretical model based on a generalized Haus master equation, we demonstrate the existence of this mode locked state without the need for saturable absorption. The fundamental physical mechanism is the interplay between self-phase modulation and anomalous dispersion like in cavity soliton together with light–matter interaction-induced time symmetry breaking.

Impact of the capture time on power saturation of quantum-well diode lasers

Injected electrons and holes are captured into quantum wells with a non-vanishing time. Simulation results are presented, showing that this results in a non-equilibrium of free and bound carriers in a diode laser. Analysis of an exemplary diode laser structure is used to show that if the capture time is too large, the carrier densities in regions adjacent to the quantum well rise strongly beyond their values at threshold at very high output power. This results in an increase of the free carrier absorption and the non-stimulated recombination, causing a reduction of the slope efficiency and a downwards-bending of the power-current characteristics (power saturation), consistent with experimental results. For the layer structure studied, the additional losses due to accumulation of holes in the n-doped region is predicted to be the dominant effect.

Intraband carrier relaxation in mid-infrared (3–4 μm) HgCdTe based structures: Effect of the carrier heating on the operating temperatures of bulk and quantum-well lasers

In this work, we study stimulated emission (SE) at 3–4 μm wavelengths from optically pumped bulk HgCdTe and HgTe/CdHgTe quantum-well heterostructures. It is proposed that, under intense excitation of such structures, energy relaxation of hot electrons occurs mostly via electron–hole scattering, while the relaxation of hot holes is direct, phonon-mediated. By balancing carrier generation/recombination and heating/cooling processes, we outline heat-induced limits to the operating temperatures of mid-IR HgCdTe lasers. Based on the existing experimental results for the SE around 3.5 μm, we predict that lasing at this wavelength may be achieved in 2.5 μm-pumped optical converters at temperatures as high as Tmax ∼ 270 K.

Dynamics of 2nd quantized state laser oscillation in gain-switched quantum-well semiconductor lasers

The dynamics of second-quantized-state laser oscillation were investigated for semiconductor laser diodes with quantum-well structures inside. We found that the second-quantized state often dominates laser oscillation instead of the first-quantized state under intensive pulse excitation, while the DC bias superposition tends to suppress the second-quantized-state oscillation. The operation characteristics were studied in detail through experimental studies and numerical calculations.

Optimization of the gain chip for optically pumped semiconductor disk lasers

Strain-compensated quantum wells (QWs) could greatly improve the performance of semiconductor disk lasers, such as improving the epitaxy quality of the semiconductor gain chip and obtaining a higher gain. To optimize the output characteristics of the semiconductor gain chip, the strain-compensated thickness, well depth, band energy, emission wavelength, and peak gain versus In and P compositions are investigated in detail. The results show that increasing the P composition of the strain-compensated layer will slightly reduce the emission wavelength, deepen the well depth, and increase the peak gain. But the P composition is not the higher the better. When designing a gain chip, it should have a pre-offset between the emission wavelength of the QWs at room temperature and the target wavelength of the laser at an intense pump, and the pre-offset values of the wavelength should be designed deliberately to guarantee the resonant periodic gain structure working normally when the temperature in the active region approaches the desired value. This theoretical investigation may provide guidance for optimizing the laser performance of semiconductor disk lasers and other QW lasers.