High-performance Laser Diodes Research Articles

High-performance PCW-DFB laser diodes using offset quantum well epitaxial structures.

We demonstrated a high-performance partially corrugated waveguide distributed feedback (PCW-DFB) laser with high output power, low relative intensity noise (RIN) and narrow linewidth. By introducing offset quantum-well structure that provides enough threshold gain difference for single transverse mode operation, the laser can achieve single mode behavior with an 8-µm-wide ridge waveguide. The laser has been designed by the simulation model based on the coupled wave equations, and the fabricated PCW-DFB laser with the cavity length of 1.3 mm exhibited an output power higher than 190 mW. Stable single mode characteristics have been achieved with a side-mode suppression-ratio (SMSR) over 55 dB. The RIN was less than -160.5 dB/Hz at an injection current of 470 mA, and the linewidth reached 45 kHz.

Study the influence mechanism of In/Ga ratio on InGaN waveguide layers during epitaxial growth

We have investigated the effect of In/Ga ratio on InGaN waveguide layers obtained by the epitaxial growth, and analyzed their physical mechanisms in detail. It is found that enhancing the In/Ga ratio by increasing the TMIn flux and reducing the TEGa flux can alleviate the decrease of In composition in InGaN waveguide. Moreover, the intensity of the yellow band of the photoluminescence is obviously reduced due to the reduction of the residual carbon impurity concentration. The smaller scattering of injected carriers by impurities and defects is beneficial for enhancing the hole concentration in the p-type layer. Meanwhile, the results of Raman spectroscopy clarify that InGaN waveguide layers grown with larger In/Ga ratio can achieve higher carrier mobility and lower resistivity. Therefore, properly increasing the In/Ga ratio during the growth can effectively improve the crystal quality of InGaN waveguide layers, which facilitates the obtaining of high-performance GaN-based laser diodes.

Optimized design of strain-compensated InxGa1-xN/GaN and InxGa1-xN/InYGa1-YN multiple-quantum-well laser diodes

We carried out a study of the strain-compensated InxGa1−xN/GaN and InxGa1-xN/InyGa1-yN multiple quantum wells, In order to carry out this analysis, we choose a set of three different types of samples. The optimization of this laser structure allowed us to determine the optimal values of the functional parameters, in order to adjust their performance and interest. We also studied the electronic and structural properties of compound semiconductor alloys used in wurtzite phase and we have presented a comparative theoretical study of both structures. Our studies show the improvement of the spontaneous emission spectra and better carrier confinement from the use of InxGa1-xN/InyGa1-yN MQW with higher In-content in barrier as active regions for diode lasers and this structure is useful for the design of new high performance Laser diodes emitting in the Blue/Violet range, and it’s also shows that the process of the electron-holes transition is strongly affected by the quantum well width and the Indium composition, and the InGaN lattice mismatch that increases with In-content causing the strain accumulation inside the QW structure. However, strain is undesirable as it can cause defects such as cracking at the interface.We can optimize the InGaN/GaN strained quantum well structures to achieve a reliable optoelectronic component. It suffices to incorporate small amounts of indium in the barrier enhances the annihilation of the defect and strain, thereby improving their structural properties.

Distributed jet array impingement boiling on particle sintered porous surfaces

Due to the excellent heat transfer performance and adaptability in dealing with local hot spots, jet array impingement boiling is promising for the high heat flux cooling in a variety of power electrical and electronic devices, such as high-performance CPU, IGBT, and laser diode. A distributed jet array with effusion ports adjacent to jet holes can extract spent flow immediately to avoid the negative crossflow effect in a normal jet array. Consequently, the heat transfer coefficient (HTC) and critical heat flux (CHF) can be both improved greatly. In order to further improve the heat transfer performance of distributed jet array impingement boiling, enhanced boiling surfaces could be used. Particle sintered porous surfaces have been widely investigated in pool boiling and achieved significant enhancement effect owing to the increased nucleation sites and wetting areas. Although several studies on the sintered porous structure have been done for jet impingement boiling, none is for distributed jet array. In this paper, a pumped two-phase loop was built up and three kinds of porous surfaces were experimentally investigated to enhance the distributed jet array impingement boiling of dielectric coolant, HFE7000. The porous structures were sintered with the copper particles of 50, 100 and 200 μm in diameter on a target surface of 11 mm ×20 mm and had a fixed thickness to particle size ratio of 2.0. A distributed jet array with 10 jet holes and 12 effusion holes was used. The diameters of the jet and effusion holes were 1 mm and 2 mm, respectively, while the distances between jet holes or effusion holes were 5 mm. The volume flow rate through the test section was 0.4 L/min, and the liquid inlet temperature and phase change saturation temperature were controlled at 35 and 60  C, respectively. An experimental apparatus was also established up to compare the wickability of the three porous surfaces. The 100 and 200 μm particles sintered surfaces were proved to have the better wickability. The experimental results turn out that the single-phase heat transfer is significantly improved due to the increased heat transfer area and flow turbulence within the porous structures, and the enhancement ratio increases with the increasing of flow rate. The porous surfaces sintered with 100 and 200 μm particles have close heat transfer performances, which are much better than that sintered with 50 μm particles. As for boiling heat transfer regime, the porous structures can provide more nucleation sites but at the same time will increase the flow resistance of effusion vapor. As a trade-off, the best performance is achieved by 100 μm particle, with its largest heat transfer coefficient upon DNB (departure from nucleate boiling) increased by 61% compared with that of the smooth surface. The wickability of porous layer however has no obvious effect on CHF due to the dominant role of distributed jet impingement on liquid feeding as well as the low surface tension of HFE7000. The maximum enhancement of CHF by 17% is acquired using the 100 μm particle sintered porous surface. Nevertheless, the heat flux range between DNB and CHF is greatly extended for the porous surfaces, which is beneficial to practical applications. A number of spots are found to be randomly distributed on the original smooth particle surfaces after many times of boiling experiments, but seem to have little influence on heat transfer performance. The long-term durability of the enhancement surface however needs further investigation.

Surface energy engineering for LiTaO3 and α-quartz SiO2 for low temperature (<220 °C) wafer bonding

Wafer bonding can be substituted for heteroepitaxy when manufacturing specific heterojunction-based devices. Devices manufactured using wafer bonding include multijunction solar cells, integrated sensors, heterogeneously integrated photonic devices on Si (such as high-performance laser diodes), Mach-Zehnder modulators, photodetectors, optical filters, and surface acoustic wave devices. In these devices, creating heterointerfaces between different semiconductors with heavily mismatched lattice constants and/or significant thermal expansion mismatch presents significant challenges for heteroepitaxial growth. High costs and poor yields in heavily mismatched heteroepitaxy can be addressed by wafer bonding in these optoelectronic devices and sensors, including the LiTaO3/Si and LiTaO3/SiO2 heterostructures. In the present work, heterostructure formation between piezoelectric LiTaO3 (100) and Si (100) and α-quartz SiO2 (100) is investigated via wafer bonding. Direct bonding is selected instead of heteroepitaxy due to a significant thermal expansion mismatch between LiTaO3 and Si-based materials. The coefficient of thermal expansion (CTE) of LiTaO3 is 18.3 × 10−6/K. This is 1 order of magnitude larger than the CTE for Si, 2.6–2.77 × 10−6/K and 25–30 times larger than the CTE for fused SiO2 and quartz (which ranges 0.54–0.76 × 10−6/K). Thus, even at 200 °C, a 4 in. LiTaO3/Si bonded pair would delaminate with LiTaO3 expanding 300 μm in length while Si would expand only by 40 μm. Therefore, direct wafer bonding of LiTaO3/Si and LiTaO3/SiO2 is investigated with low temperature (T < 500 K) Nano-Bonding™, which uses surface energy engineering (SEE). SEE is guided by fast, high statistics surface energy measurements using three liquid contact angle analysis, the van Oss/van Oss–Chaudhury–Good theory, and a new, fast Drop Reflection Operative Program analysis algorithm. Bonding hydrophobic LiTaO3 to hydrophilic Si or SiO2 is found to be more effective than hydrophilic LiTaO3 to hydrophobic Si or SiO2 temperatures for processing LiTaO3 are limited by thermal decomposition LiTaO3 into Ta2O5 at T ≥ 180 °C due to Li out-diffusion as much as by LiTaO3 fractures due to thermal mismatch.

Green laser diodes with constant temperature growth of InGaN/GaN multiple quantum well active region

Increasing trench defect density in green InGaN/GaN multiple quantum wells (MQWs) has been reported to be one cause for “green gap” and creates a challenge in fabricating high-performance green laser diodes (LDs). In this article, we report methods to suppress the density of trench defects. Suppressed defect density in InGaN/GaN MQWs results in greatly improved optical quality, as indicated by increasing photoluminescence (PL) intensity and nonradiative recombination lifetime, and decreasing PL full-width-half-maximums (FWHMs), which can be as narrow as 113 meV. This enabled constant temperature growth of the InGaN/GaN MQW active region of the green LD structure and greatly improved slope efficiency.

Lattice-Matched AlInGaN Electron-Blocking Layer Embedded in High-Performance GaN-based Light-Emitting Devices

We report on high-performance GaN-based laser diodes (LDs) with a lattice-matched AlInGaN electron blocking layer (EBL) instead of a p-AlGaN EBL. In the low injection current region, the intensity of the electroluminescence (EL) of the LDs with a p-AlGaN EBL was slightly higher than that of the LDs with a p-AlInGaN EBL. However, the EL intensity of the LD with a p-AlInGaN EBL was higher than that of the LD with a p-AlGaN EBL with increasing injection current. Further, the lasing performance of the LD with a p-AlInGaN EBL was better than that of the LD with a p-AlGaN EBL at higher injection currents. From these results, we suggest that the lattice-matched AlInGaN EBL enhances the high-power performance by reducing the droop phenomenon in the light-emitting device.

Suppression the Leakage of Optical Field and Carriers in GaN-based Laser Diodes by using InGaN Barrier Layers

GaN-based laser diodes (LDs) with different barrier layers are investigated by using simulation and experimental methods. it is found that the absorption loss always decreases with the increasing indium content of the InGaN barrier layer in InGaN/InGaN multiquantum well (MQW) LDs, It leads to an increase of slope efficiency and output power of LDs due to the better optical confinement effect of laser beam. However, when the barrier layer changes from InGaN to AlGaN, both threshold current and slope efficiency deteriorate seriously. Except for the increase of the optical absorption loss resulting from the leakage of the optical field, a large leakage of carriers due to the increased piezoelectric polarization field in InGaN/AlGaN MQW region may also be responsible for this deterioration. Therefore, suppressing the leakage of the optical field and carriers by using relatively higher In content InGaN barrier layer is benefit for obtaining high-performance LDs with low threshold current and high output power.

Electrically pumped ultraviolet lasing in polygonal hollow microresonators: investigation on optical cavity effect.

Electrically driven ultraviolet lasing was realized in two-dimensional ZnO nanowall networks from Au/MgO/n-ZnO/n-GaN/In structure, and whispering gallery type resonant modes are responsible for the lasing action. We present a comparative study on lasing action based on nanowall networks with different micro-hole sizes. The representative diode (Device II) with a moderate micro-hole size exhibits an ultralow threshold current density of 1.01 A/cm2, and the lasing action can be sustained at a temperature up to ∼413 K, showing a good temperature tolerance. Moreover, the corresponding characteristic temperature for Device II was derived as ∼91.4 K. It can be qualitatively anticipated that this work will provide instructive guidelines for fabrication and development of high-performance ultraviolet laser diodes by using two-dimensional ZnO nanowall networks as the lasing gain media.

Optically pumped 1.3 μm room-temperature InAs quantum-dot micro-disk lasers directly grown on (001) silicon.

Direct integration of high-performance laser diodes on silicon will dramatically transform the world of photonics, expediting the progress toward low-cost and compact photonic integrated circuits (PICs) on the mainstream silicon platform. Here, we report, to the best of our knowledge, the first 1.3 μm room-temperature continuous-wave InAs quantum-dot micro-disk lasers epitaxially grown on industrial-compatible Si (001) substrates without offcut. The lasing threshold is as low as hundreds of microwatts, similar to the thresholds of identical lasers grown on a GaAs substrate. The heteroepitaxial structure employed here does not require the use of an absorptive germanium buffer and/or dislocation filter layers, both of which impede the efficient coupling of light from the laser active regions to silicon waveguides. This allows for full compatibility with the extensive silicon-on-insulator (SOI) technology. The large-area virtual GaAs (on Si) substrates can be directly adopted in various mature in-plane laser configurations, both optically and electrically. Thus, this demonstration represents a major advancement toward the commercial success of fully integrated silicon photonics.

Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X-ray Diffraction Microscopy.

Advanced semiconductor heterostructures are at the very heart of many modern technologies, including aggressively scaled complementary metal oxide semiconductor transistors for high performance computing and laser diodes for low power solid state lighting applications. The control of structural and compositional homogeneity of these semiconductor heterostructures is the key to success to further develop these state-of-the-art technologies. In this article, we report on the lateral distribution of tilt, composition, and strain across step-graded SiGe strain relaxed buffer layers on 300 mm Si(001) wafers treated with and without chemical-mechanical polishing. By using the advanced synchrotron based scanning X-ray diffraction microscopy technique K-Map together with micro-Raman spectroscopy and Atomic Force Microscopy, we are able to establish a partial correlation between real space morphology and structural properties of the sample resolved at the micrometer scale. In particular, we demonstrate that the lattice plane bending of the commonly observed cross-hatch pattern is caused by dislocations. Our results show a strong local correlation between the strain field and composition distribution, indicating that the adatom surface diffusion during growth is driven by strain field fluctuations induced by the underlying dislocation network. Finally, it is revealed that a superficial chemical-mechanical polishing of cross-hatched surfaces does not lead to any significant change of tilt, composition, and strain variation compared to that of as-grown samples.

Nitrogen Effect on the Frequency Shift in Indium-GaAsN Quantum Wells Laser

The GaAsN/GaAs material system has recently been investigated as material for the realization of high-performance laser diodes emitting at the optical fiber window. Nitrogen content in GaAsN has a great influence on the band gap in this semiconductor. The knowledge of influence of nitrogen on optical transition energies in GaAsN/GaAs Quantum Wells (QWs) or Quantum Dots (QDs) structures is very important due to the possibility of adjustment of the optical transition energies to the telecommunication wavelength range when the system GaAsN is submitted to further indium elements giving rise to the quaternary alloys (In)GaAsN. The purpose of this work is to solve the coupled nonlinear rate equations describing the complex electric field and the carrier density in a simple model of the GaNxAs1-x or (In)GaAsN semiconductor laser. The model is sufficient to account for many of the observed dynamics in a single mode semiconductor laser in response to a dynamic drive current, such as relaxation oscillations and frequency chirping.

Growth of homogeneous semiconductor mixed crystals by the traveling liquidus-zone method

Compositionally uniform mixed crystals of InxGa1−xAs (0.07<x<0.35) and Si0.5Ge0.5 were grown by the traveling liquidus-zone (TLZ) method. The TLZ method is a kind of zone-melting method but is different from a conventional method in forming a liquidus-zone at a relatively low temperature gradient of about 10°C/cm. In the paper, the principle of the TLZ method, examples of TLZ-grown crystals and merits and demerits of the TLZ method are described. Finally, application of the TLZ-grown In0.13Ga0.87As crystals to substrates and successful fabrication of high performance laser diodes are introduced.

Fabrication of a novel silica PLC hybrid integrated triplexer

A new-style silica planar lightwave circuit (PLC) hybrid integrated triplexer, which can demultiplex 1490-nm download data and 1550-nm download analog signals, as well as transmit 1310-nm upload data, is presented. It combines SiO2 arrayed waveguide gratings (AWGs) with integrated photodetectors (PDs) and a high performance laser diode (LD). The SiO2 AWGs realize the three-wavelength coarse wavelength-division multiplexing (CWDM). The crosstalk is less than 40 dB between the 1490- and 1550-nm channels, and less than 45 dB between 1310- and 1490- or 1550-nm channels. For the static performances of the integrated triplexer, its upload output power is 0.4 mW, and the download output photo-generated current is 76 A. In the small-signal measurement, the upstream 3-dB bandwidth of the triplexer is 4 GHz, while the downstream 3-dB bandwidths of both the analog and digital sections reach 1.9 GHz.

Dicing of gallium–arsenide high performance laser diodes for industrial applications

Dicing of III–V based high-power laser diodes is commonly carried out in two steps. To start with, an initial defect is created in the devices by scratching it with a sharp diamond tip to allow a subsequent cleavage operation. Micro-scratching and cleavage are crucial operations for maximizing the yield production. Thus, this contribution is divided into two papers according to these essential operations. The cleavage operation is the focus of this study for three material conditions based on gallium–arsenide (GaAs) previously scratched by a diamond tip (Berkovich). Due to its complexity, the cleavage operation was investigated through (a) finite element calculation, (b) the stress intensity factor K and (c) the cleavage operation itself. It can be demonstrated that a crack significantly diminishes the influence of loading condition. Additionally, three cleavage behaviors were observed depending on the initial conditions. First, the crack deviates from its path. This was observed when the shear stress component becomes more important than the tensile stress. Second, features are visible on the cleaved surface. This is generally the case when the median crack is small resulting in an unstable crack growth leading to catastrophic failure. Finally, perfectly atomic flat cleaved surfaces are produced. This is the case with larger median crack when, after unstable initiation, crack propagation is controlled. The analyzes and results of the scratching operation completed in this contribution are presented in Part I [Wasmer, K., Ballif, C., Pouvreau, C., Schulz, D., Michler, J., 2008. Dicing of gallium–arsenide high performance laser diodes for industrial applications. Part I. Scratching operation. J. Mater. Process. Technol. 198, 114–121]. Based on this complete study, three technological requirements can be set for obtaining cleaved surface atomically flat: (1) crack initiation and propagation must be controlled, even in brittle semiconductors such as GaAs, (2) the scratch load range and tip geometry must be optimized to avoid particle generation and (3) finally, crack opening in Mode I (tension) must be maximized compared to Mode III (shearing).

High-Performance Blue InGaN Laser Diodes With Single-Quantum-Well Active Layers

The authors report on the high-performance blue laser diodes (LDs) with an emission wavelength of ~448 nm employing InGaN single-quantum-well (QW) active layers. At 100-mW continuous-wave (CW) output power, operation current and voltage are, respectively, 150 mA and 5.3 V, corresponding to the wall plug efficiency of >12%, a record value for the single-mode InGaN LDs with blue wavelengths. The single QW blue LD showed normal temperature dependence of light output-current curves with the characteristic temperature of 170 K. In addition, we demonstrate a high level of catastrophic optical damage of >300 mW and long device lifetime under CW operation condition at room temperature.

Dicing of gallium–arsenide high performance laser diodes for industrial applications

Abstract Mechanical separation of III–V based high power laser diodes is generally performed in two steps. First, the devices are scratched with a sharp diamond tip followed by a cleavage operation. Micro-scratching and cleavage are key operations for maximizing the yield production and so this contribution is divided into two papers according to these fundamental operations. In this paper, the micromechanics of micro-scratching and particle generation were examined for three material conditions based on gallium–arsenide (GaAs) as well as three geometries of diamond tips (cube corner, conical and Berkovich). This goes from the plastic deformation through in situ observations of micro-scratches to examination of subsurface cracks. The main conclusion is that the depth of the initial defect, also called median crack (a), is well described by the power-law PS ∝ a3/2, where PS is the scratching load. Additionally, when the scratching load became too important, the surface was damaged due to the sharp angles of the indenter tip resulting in a median crack having an uneven depth and where stress concentration appeared due to the plugging of the tip. Moreover, it was found that the initial defect is sensitive to the material conditions. The data analysis of the cleavage operation obtained from scratches performed in this work is presented in Part II [Wasmer, K., Ballif, C., Pouvreau, C., Schulz, D., Michler, J., 2008. Dicing of gallium–arsenide high performance laser diodes for industrial applications. Part II. Cleavage operation, J. Mater. Process. Technol. 198, 105–113]. Based on this complete study, three technological requirements can be set for obtaining cleaved surface atomically flat: (1) crack initiation and propagation must be controlled, even in brittle semiconductors such as GaAs, (2) the scratch load range and tip geometry must be optimized to avoid particles generation and (3) finally, crack opening in Mode I (tension) must be maximized compared to Mode III (shearing).

Development of High-Performance Laser Diode for Pumping Solid-State Laser

The spectral bandwidth of a broad-area laser diode is effectively suppressed by use of an off-axis external-cavity technique. The external cavity consisted of a rod lens, a cylindrical lens and a volume Bragg grating. The laser beam has 5.8-fold improvement in spectral bandwidth and its peak power versus wavelength is effectively enhanced. On the basis of this technique, we focus the beam of the high-power laser diode to effectively end pump a solid-state laser.

High-performance laser diodes with emission wavelengths above 1100 nm and very small vertical divergence of the far field

The effect of variations in the vertical structure on the performance of AlGaAs-GaAs laser diodes with an InGaAs quantum well (QW) emitting around 1120 nm was investigated. With very thick waveguide layers, more than 95% of the output power is enclosed in an angle smaller than 35/spl deg/. This allows the use of fast axis collimators with a small numerical aperture. Broad area laser diodes with 100-/spl mu/m stripe width, an optimized doping profile, and a double QW emit more than 12 W and show reliable operation at 5 W.

High-efficient carbon-doped InGaAs/AlGaAs/GaAs quantum well lasers

The carbon-doping behaviors of carbon tetrabromide (CBr4) in AlxGa1−xAs material system are studied by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Doping level dependence on growth temperature, and V/III ratio is established. C-doped InGaAs/AlGaAs/GaAs separate confinement laser structure (∼940nm) are grown and demonstrated high quality with low-threshold current density. High-performance monolithic laser diode arrays are fabricated. A high slope efficiency of 1.17W/A and power efficiency of 62% are achieved, which is much better than the performance of Zn-doped structure of the same design. Therefore, carbon doping is demonstrated to have unique advantages over Zn-doping for high-power semiconductor laser applications.