Design Of Laser Diodes Research Articles

Optimum Design of InGaN Blue Laser Diodes with Indium-Tin-Oxide and Dielectric Cladding Layers.

The efficiency of current GaN-based blue laser diodes (LDs) is limited by the high resistance of a thick p-AlGaN cladding layer. To reduce the operation voltage of InGaN blue LDs, we investigated optimum LD structures with an indium tin oxide (ITO) partial cladding layer using numerical simulations of LD device characteristics such as laser power, forward voltage, and wall-plug efficiency (WPE). The wall-plug efficiency of the optimized structure with the ITO layer was found to increase by more than 20% relative to the WPE of conventional LD structures. In the optimum design, the thickness of the p-AlGaN layer decreased from 700 to 150 nm, resulting in a significantly reduced operation voltage and, hence, increased WPE. In addition, we have proposed a new type of GaN-based blue LD structure with a dielectric partial cladding layer to further reduce the optical absorption of a lasing mode. The p-cladding layer of the proposed structure consisted of SiO2, ITO, and p-AlGaN layers. In the optimized structure, the total thickness of the ITO and p-AlGaN layers was less than 100 nm, leading to significantly improved slope efficiency and operation voltage. The WPE of the optimized structure was increased relatively by 25% compared to the WPE of conventional GaN-based LD structures with a p-AlGaN cladding layer. The investigated LD structures employing the ITO and SiO2 cladding layers are expected to significantly enhance the WPE of high-power GaN-based blue LDs.

Comparison of high power red-emitting diode laser designs for medical applications

A comparison is made between, on the one hand, the red-emitting laser structure currently widely used for medical applications and based on an ultranarrow waveguide layer with a compressively strained QW active layer in it and, on the other hand, the red emitting laser using a broadened asymmetric waveguide structure with a bulk active layer near the p-cladding, proposed by us. It is shown that the proposed design promises substantial improvements over the ultranarrow one including lower series and thermal resistances, and higher catastrophic degradation threshold, while maintaining relatively narrow far field and allowing the typical power required for medical applications to be achieved at lower currents, particularly at elevated temperatures.

Picosecond and high-power UV/Vis light pulsing using gallium nitride field-effect transistors: implementation and design evaluation

This paper discusses the development of cost-effective and high-performance picosecond and high-power light pulsers. The use of innovative gallium nitride field-effect transistor technology, in combination with meticulous electronic design and careful selection of light-emitting diodes or laser diodes for ultraviolet and visible spectral ranges, has resulted in superior characteristics compared to commonly used designs. The sub-ns design achieves pulse widths as low as 300 ps, with photon outputs ranging between 104-109 photons per pulse, over a wavelength range of 235-470 nm. Meanwhile, the high-power design achieves pulse widths as low as 1.8 ns, with photon outputs ranging between 107-1011 photons per pulse, and a wavelength range of 375-525 nm. The two designs complement each other in photon outputs, covering a dynamic range of almost ten orders of magnitude. This paper provides an evaluation of the electrical design and emitter selection of both pulsers, as well as their electrical and optical performance.

A fiber-coupled laser diode design for reflection mode optical resolution photoacoustic microscopy

Pulsed Laser Diodes (PLD) are compact and high pulse repetition rate laser sources that show a great potential for low-cost Optical Resolution Photoacoustic Microscopes (OR-PAM). Nevertheless, their non-uniform multimode laser beams are of low quality so that high lateral resolutions with tightly focused beams are difficult to realize at long focusing distances, as required for reflection mode OR-PAM devices of clinical application. A new strategy based on homogenizing and shaping the laser diode beam with a square-core multimode optical fiber allowed to attain competitive lateral resolutions while keeping one centimeter working distance. The theoretical expressions for the laser spot size, determining optical lateral resolution, and the depth of focus are also written for general multimode beams. An OR-PAM system was built in confocal reflection mode with a linear phased-array as the ultrasound receiver in order to test its performance, first, on a resolution test target and, afterwards, on ex vivo rabbit ears to show the system potential for subcutaneous imaging of blood vessels and hair follicles.

Performance enhancement of an AlGaN-based deep-ultraviolet laser diode using a two-stepped doped lower waveguide

Subject of study. The performance of a deep-ultraviolet laser diode is improved using a two-stepped Si-doped lower waveguide. Method. The impact of the variations on AlGaN-based deep-ultraviolet laser diodes has been evaluated based on the simulated results after theoretical calculations. The two AlGaN-based ultraviolet laser diodes as a traditional device and the proposed device have been analyzed comparatively based on their performance within a nomination wavelength region range of 269–280 nm. Main results. Using a two-stepped Si-doped lower waveguide, the lasing threshold current decreases in the proposed device D2 in comparison to the traditional device D1. The operating threshold voltage of D1 is 13.8 V, and that of D2 is 4.24 V, respectively, with lasing threshold currents of 0.4 A and 0.002 A, respectively. Practical significance. The optimization of the design of AlGaN-based ultraviolet laser diodes following the perfect bulk aluminium nitride substrate in the traditional device is the crucial factor of the practical significance of the scientific field utilized in the proposed device. The performance of deep-ultraviolet laser diodes is improved when a suitably constructed two-stepped Si-doped lower waveguide substitutes the traditional lower waveguide. The noted improvements are the reduction in total optical loss with the improved optical confinement factor. These are primarily due to an increase in the hole injection current and a decrease in the electron leakage current.

Polarization Doping in a GaN-InN System-Ab Initio Simulation.

Polarization doping in a GaN-InN system with a graded composition layer was studied using ab initio simulations. The electric charge volume density in the graded concentration part was determined by spatial potential dependence. The emerging graded polarization charge was determined to show that it could be obtained from a polarization difference and the concentration slope. It was shown that the GaN-InN polarization difference is changed by piezoelectric effects. The polarization difference is in agreement with the earlier obtained data despite the relatively narrow bandgap for the simulated system. The hole generation may be applied in the design of blue and green laser and light-emitting diodes.

Distributed Bragg reflector lasers emitting between 696 and 712 nm

The authors report on design, fabrication, and electro-optical characterization of single-frequency diode lasers emitting around 696, 707, and 712 nm. This has been achieved by a variation of the periods of the 10th order surface Bragg gratings implemented on a single epitaxial wafer. Depending on the wavelength, the devices achieved an optical output power of up to 60 mW at a current of 150 mA and spectral linewidths of about 400 kHz (full width at half maximum (FWHM)) and 20 kHz (Lorentzian).

Designs for III-nitride edge-emitting laser diodes with tunnel junction contacts for low internal optical absorption loss

The lasing mode and internal optical absorption loss profiles of III-nitride edge-emitting laser diode (LD) designs operating at 440 nm were modeled using the transfer matrix method. These models indicate absorption losses are minimized in LDs utilizing tunnel junction (TJ) contacts that (1) optimize the TJ to be as close to fully depleted as possible; (2) spatially separate the metal contact from the lasing mode using lightly doped n-GaN located above the TJ; (3) in designs with optimized TJs, minimize the total thickness of p-type material. These features reduce absorption losses in the model, relative to comparable LD models with an unoptimized TJ contact or with a transparent conducting oxide p-contact, by up to 15.3% and 12.5%, respectively, while at the same time eliminating most or nearly all p-type material.

Electrically injected GeSn lasers with peak wavelength up to 2.7 μm

GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-IV direct-bandgap material. The GeSn laser study recently moved from optical pumping into electrical injection. In this work, we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions. Cap layer material was studied by using Si 0.03 Ge 0.89 Sn 0.08 and Ge 0.95 Sn 0.05 , and cap layer total thickness was also compared. The 190 nm SiGeSn-cap device had threshold of 0.6 kA / cm 2 at 10 K and a maximum operating temperature ( T max ) of 100 K, compared to 1.4 kA / cm 2 and 50 K from 150 nm SiGeSn-cap device, respectively. Furthermore, the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA / cm 2 and T max at 90 K, i.e., higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer, indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably. The study of the active region material showed that device gain region using Ge 0.87 Sn 0.13 had a higher threshold and lower T max , compared to Ge 0.89 Sn 0.11 . The performance was affected by the metal absorption, free carrier absorption, and possibly defect density level. The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge 0.87 Sn 0.13 in gain regions. The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-IV photonics on a Si platform.

Dual gate material (Au and Pt) based double-gate MOSFET for high-speed devices

Aluminium Gallium Arsenide (AlGaAs) is a semiconductor material used in the latest design of double heterostructure laser diodes. This semiconductor is mostly available in the arbitrary alloy form between Gallium Arsenide and Aluminium Arsenide. It is derived from the Tri-MethylGallium (TMG/TMGa), and Arsine (AsH3), both the chemicals are pyrophoric and toxic. The resistance is less between source and drain contacts in the case of AlGaAs so that it has been proposed as a material to grow contacts on Indium Phosphide (InP) layer. The AlGaAs uses an ion implantation model for a design purpose which lowers the thermal power while the operation of the device. The parasitic capacitance has to be taken care of while designing a device using this material since the capacitance affects much in the AlGaAs based devices. The average velocity of the electrons has been observed to be increased by 14.63 % in the Au-gate (gate-1) and Pt-gate (gate-2) material-based Double-Gate (DG) MOSFET compared to the Silicon-based DG MOSFET. This paves the way for higher electron mobility, in turn, it can be used in highfrequency device manufacturing. The proposed material can be used in high-speed hybrid applications such as HEMTs and radiofrequency devices for long-haul communication.

AlGaAs/GaAs asymmetric‐waveguide, short cavity laser diode design with a bulk active layer near the p ‐cladding for high pulsed power emission

It is shown theoretically that a GaAs/AlGaAs laser diode design using an asymmetric waveguide structure and a bulk active layer (AL), located close to the p-cladding, can provide high output power in a single, broad transverse mode for short-wavelength (<0.9 μm, matching the spectral range of high efficiency of silicon photodetectors) pulsed emission in the nanosecond pulse duration region, typically <<100 ns. The dependences of the laser performance on the thickness of the AL and the cavity length are analysed. It is shown that the relatively thick bulk AL allows the of short cavity lengths (<1 mm), for achieving high pulsed power while maintaining a relatively low series resistance and a narrow far field.

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.

Influence of pump beam shaping and noise on performance of a direct diode-pumped ultrafast Ti:sapphire laser.

One of the major factors that limits the widespread use of ultrafast titanium sapphire (Ti:S) lasers in life science is its expensive and complex pump source. Broad area diode laser (BA-DL) based pump sources have high potential to solve this problem, since they are compact, inexpensive and very efficient. However, their non-diffraction limited beam profile makes it challenging to achieve high powers in Kerr-lens mode-locked (KLM) operation of Ti:S lasers. In this work, we show that the ideal way to beam shape two spectrally combined BA-DLs with different beam qualities is to aim for a compromise between matching to the cavity mode diameter and the cavity mode Rayleigh range. We furthermore conclude that the relative intensity noise (RIN) of the BA-DL pumped Ti:S laser, another important parameter for imaging applications, is sufficiently low for a wide range of life science applications. However, for applications that are highly sensitive to noise, new laser diode designs are likely necessary to reduce inherent noise originating within the laser diode.

High-Powered Diode Lasers—New, Bright and Blue

Blue diode laser designs with kW powers are advancing in industrial processing applications, including cutting, welding and foil joining of copper and other high-reflectance materials.

Design and growth of GaN-based blue and green laser diodes

GaN-based laser diodes (LDs) extend the wavelength of semiconductor LDs into the visible and ultraviolet spectrum ranges, and are therefore expected to be widely used in quantum technology, bio & medical instruments, laser displays, lighting and materials processing. The development of blue and green LDs is still challenging, even though they are based on the same III-nitride materials as GaN-based light-emitting diodes. The challenges and progress of GaN-based blue and green LDs are reviewed from the aspects of epitaxial growth and layer structure design. Due to large differences in lattice constants and growth conditions for InN, GaN, and AlN, considerable effort is required to improve the quality of InGaN multiple quantum well (MQW) gain medium for blue and especially green LDs. p-type doping profiles, conditions and layer structures are critical to reduce the internal losses and to mitigate the degradation of InGaN MQWs. Hole injection is also a key issue for GaN-based LDs.

Design of a 10 kW level diode laser optical stack with a line shape beam spot.

We designed and simulated a diode laser with output power of more than 10 kW and a line shape beam spot of approximately ${14 - 58}\;{\rm mm} \times {1.6}\;{\rm mm}$14-58mm×1.6mm (${{\rm 1/e}^2}$1/e2 width). The diode laser was assembled with high fill factor diode laser bars that can be cooled with filtered tap water. The diode laser bar was beam shaped with a tilted cylindrical lens array to twist the slow axis of individual emitters by 90 deg, and then the slow axis was collimated with a single cylindrical lens. From the simulation, 20 laser diode bars with the same wavelength formed a diode laser optical stack with an output power of more than 3.5 kW, a beam spot of ${31}\;{\rm mm} \times {12}\;{\rm mm}$31mm×12mm size, and full divergence angles of around 6 mrad in both the horizontal and vertical directions. Then, three laser diode optical stacks with different wavelengths were wavelength-multiplexed to obtain an output power of more than 10 kW. Finally, the diode laser optical stack was transformed by simple cylindrical lenses to form a line shape spot with a working distance longer than 250 mm. Our diode laser design is much simpler than previous devices with similar output power and can find various applications such as high-speed laser cladding.

Near vacuum-ultraviolet aperiodic oscillation emission of AlN films

An accurate measurement of the refractive index is necessary for the optical design of both deep ultraviolet laser diodes and light-emitting diodes. Generally, the refractive indices along different crystallographic axes of anisotropic thin films are measured using variable angle spectroscopic ellipsometry. However, there are still some limitations concerning this method. Here we proposed a potential method to measure the band edge refractive index of wide bandgap semiconductor. An aperiodic oscillation emission phenomenon due to the Fabry-Perot effect was observed in the fluorescence spectrum of an AlN film with a thickness of 1500 nm. Based on the characteristics of the fluorescence spectrum and the definition of Fabry-Perot effect, we obtained the ordinary refractive index of the AlN thin film near the band edge directly. This refractive index measurement method is a supplement to the variable angle ellipsometry, and it is a more direct and effective method for transferred film and thinner samples to measure the fluorescence spectrum.

AlGaN nanocrystals: building blocks for efficient ultraviolet optoelectronics

AlGaN nanocrystals have emerged as the building blocks of future optoelectronic devices operating in the ultraviolet (UV) spectral range. In this article, we describe the design and performance characteristics of AlGaN nanocrystal UV light-emitting diodes (LEDs) and surface-emitting UV laser diodes. The selective-area epitaxy and structural, optical, and electrical properties of AlGaN nanocrystals are presented. The recent experimental demonstrations of AlGaN nanocrystal LEDs and laser diodes are also discussed.

Strain compensation in a semiconducting device structure using an intentionally mismatched uniform buffer layer

The extent of strain relaxation in semiconducting device heterostructures has important implications in the design of high electron mobility transistors, light-emitting diodes, and laser diodes, in which the residual strain affects the device characteristics. In this work, we develop the theoretical framework for understanding strain compensation in a semiconductor device layer using a uniform buffer layer which can be intentionally mismatched to the material above. Specifically, we determined the critical condition for complete strain compensation in the device layer by intentionally introducing a compositional mismatch at the device-buffer interface. We present minimum energy calculations and show that for a given device layer with fixed mismatch and layer thickness, the buffer layer may be designed with the appropriate combination of thickness and mismatch such that the device layer will have zero residual strain in equilibrium. Such a structure can be referred to as a completely strain-compensated design. In the more general case, there may be partial strain compensation, and we give a simple physics-based Gaussian-type function describing the residual strain in the device layer. We have applied this general framework to InxGa1−xAs/GaAs (001) heterostructures for the purpose of illustration, but the work is applicable to any diamond or zinc blende (001) heteroepitaxial material system.

Transparent conducting oxide clad limited area epitaxy semipolar III-nitride laser diodes

The bottom cladding design of semipolar III-nitride laser diodes is limited by stress relaxation via misfit dislocations that form via the glide of pre-existing threading dislocations (TDs), whereas the top cladding is limited by the growth time and temperature of the p-type layers. These design limitations have individually been addressed by using limited area epitaxy (LAE) to block TD glide in n-type AlGaN bottom cladding layers and by using transparent conducting oxide (TCO) top cladding layers to reduce the growth time and temperature of the p-type layers. In addition, a TCO-based top cladding should have significantly lower resistivity than a conventional p-type (Al)GaN top cladding. In this work, LAE and indium-tin-oxide cladding layers are used simultaneously in a (202¯1) III-nitride laser structure. Lasing was achieved at 446 nm with a threshold current density of 8.5 kA/cm2 and a threshold voltage of 8.4 V.