Short-wavelength Laser Diodes Research Articles

InGaN Laser Diodes-Gain, Spectra and Nonlinear Dynamics

In this era, short-wavelength laser diodes with quantum-well (QW) structures offer plenty of opportunities for improvement in laser performance and receive widespread attention. Therefore, we develop dynamic model of the violet-blue InGaN laser diodes (LDs) and discuss basic features of the device in this paper. We investigate longitudinal mode dynamics through detail numerical simulation of the rate equation model of the quantum-well LDs. We selectively observe several effects such as relaxation oscillation, mode competition, intensity noise etc. From the dynamic behavior of the gain spectrum and time-varying modal photon numbers we found that the higher intensity noise of the quantum-well structure was due to random fluctuation with time among the different modes. The results were explained considering the previously published findings to confirm the validity of the proposed rate equation model of the quantum-well structures. DUJASE Vol. 7 (2) 62-67, 2022 (July)

Magneto-optical properties of wider gap semiconductors ZnMnTe and ZnMnSe films prepared by MBE

The II-VI based magnetic semiconductors with a direct and wide optical bandgap are expected to show high potential for optical applications utilizing short wavelength laser diodes (LDs), such as 532-nm green and 475-nm blue LDs. We have confirmed that the Faraday rotation θF in the ZnMnTe and ZnMnSe films deposited on quartz glass (QG) and sapphire (SA) substrates by using molecular beam epitaxy (MBE) is large near the absorption edge. This paper reports the magneto-optical properties of ZnMnTe and ZnMnSe films synthesized on the QG and SA substrates, and shows the result of a direct Faraday rotation observation successfully made for the ZnMnTe films under 1.28-kHz alternating magnetic fields. The optical absorption characteristics of the ZnMnTe films grown on the SA substrates by MBE are discussed by comparing them with the optical absorption properties and photoluminescence spectra of the II-VI ZnTe parent single crystals.

Investigation on the materials of heavily Mg-doped AlInP layers for laser diode structure

High concentration p-type AlInP material is an important layer to achieve low resistant and large carrier confinement in short-wavelength red-light laser diodes (LDs). To investigate the Mg doping behavior and other characteristics in the red-light LDs with tensile GaInP well structure, two LDs wafers with different Mg-doped AlInP cladding layers were grown by the metalorganic chemical vapor deposition (MOCVD) method. Incorporation and activation behavior of Mg atoms in heavily-doped AlInP were analyzed by the comparisons between hole concentration and atom concentration. We demonstrate that it is possible to achieve hole concentration above 1018 cm−3 using Mg dopant in AlInP layers just by an in-situ annealing. Furthermore, a hole concentration as high as 2.92 × 1018 cm−3 was achieved after post rapid thermal annealing in the N2 atmosphere, which is the highest hole doping concentrations reported to-date for the p-AlInP material.

PERFORMANCE EVALUATION OF ZNO DOPED DIDYMIUM NANO POWDER SAMPLES

In the recent years, much attention has been focused on wide band gap semiconductors materials because of their excellent potential for blue light emitting devices, short-wavelength laser diodes and detectors in UV-blue spectral region. The wide band gap ZnO is gaining much importance for the possible application due to the capability of ultraviolet lasing at room temperature and possibilities to engineer the band gap for further use. In order to attain the potential offered by ZnO, both high-quality n-and p-type ZnO are essential. In this work we synthese the ZnO nanopowder by Sol–gel method & after that the ZnO is doped with rare earth material didymium. Didymium is a naturally occurring element with major constituent Nd and Pr and is used in many applications. The FTIR, SEM and EDX characterization techniques are applied to study the sample & it has been found that the formation of pure phase of ZnO having wurtzite hexagonal structure occurs at 1%, But at higher concentration of Di (3%, 5%) the system shows mixed phase. Moreover SEM shows that the Di doped ZnO has well ordered morphology, has low aggregation and homogeneous distribution of particle size. Note that the synthesized system is also having band gap of 3.24 eV which is comparable with the standard value.

Hydrogenic Donor Binding Energy in a Strained BxGa1-xN/BN Quantum well

Group III nitride materials are well known for their superior thermal, mechanical and optical properties. They can be used for short-wavelength light-emitting diodes, laser diodes and optical detectors and high electron mobility transistors and they have a high melting point, high thermal conductivity, a stronger resistance to oxidation at high temperatures and transparency to a large spectrum. Group III-Nitride alloys can be easily integrated in integrated electronic systems including current amplifiers. In the present work, the binding energy of a hydrogenic donor is studied taking into account the geometrical confinement and the various Boron alloy content. GaN semiconducting material acts as the inner quantum well material whereas BN material acts as the outer barrier material. The energy eigen values and binding energy of a hydrogenic donor are obtained using variational technique within a single band effective mass approximation.

Laser Operation of Nitride Laser Diodes with GaN Well Layer in 340 nm Band

We have reported the laser operation of a short-wavelength ultraviolet laser diode with multiple quantum wells composed of GaN well layers. The GaN well-width is estimated to be around 1–1.5 nm. We have simulated whole laser-diode structure, and calculated wave-function overlap integrals. It is provided the integral becomes the maximum value in the well-width of 1.5 nm. The laser operation has been achieved in 340-nm-band under the pulsed current mode at room temperature. The wavelength is far from the wavelength corresponding to band gap of GaN, and the shortest lasing wavelength ever reported for a semiconductor laser composed of binary compound well layer. Moreover, the device has been realized on an Al0.2Ga0.8N underlying layer with 0.1 lower AlN mole fraction margin than that of a previous reported 342 nm laser-diode with an Al0.3Ga0.7N underlying layer. These results provide a chance to the next stage for a shorter-wavelength ultraviolet laser diode.

A 340-nm-band ultraviolet laser diode composed of GaN well layers

We have demonstrated the laser operation of a short-wavelength ultraviolet laser diode with multiple-quantum-wells composed of GaN well layers. The laser action has been achieved in 340-nm-band far from the wavelength corresponding to GaN band gap under the pulsed current mode at room temperature. The device has been realized on the Al(0.2)Ga(0.8)N underlying layer. The AlN mole fraction of the underlying layer is 0.1 lower than that of the underlying layer which was used for the previously reported 342 nm laser diode. These results provide a chance to the next step for a shorter-wavelength ultraviolet laser diode.

Aligned growth of ZnO nanowires by NAPLD and their optical characterizations

Not only vertically aligned ZnO nanowires but also horizontally aligned ZnO nanowires have been successfully grown on the annealed (0 0 0 1) c-cut and (1 1 2 0) a-cut sapphire substrates, respectively using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The as-synthesized ZnO nanowires exhibit an ultraviolet emission at around 390 nm and the absent green emission under room temperature. The single ZnO nanowire was collected in the electrode gap by dielectrophoresis (DEP). Under the optical pumping, the single ZnO nanowire exhibited UV emission at around 390 nm with several sharp peaks whose energy spacings are almost constant, which greatly differs from the broad UV emission of the film with many nanowires, suggesting ZnO nanowires as candidates for laser media. The single ZnO nanowire showed polarized photoluminescence (PL). The as-synthesized ZnO nanowires could find many interesting applications in short-wavelength light-emitting diode (LED), laser diode and gas sensor.

A 342-nm ultraviolet AlGaN multiple-quantum-well laser diode

The realization of semiconductor laser diodes and light-emitting diodes that emit short-wavelength ultraviolet light is of considerable interest for a number of applications including chemical/biochemical analysis, high-density data storage and material processing. Group III nitride materials are one of the most promising candidates for fabricating such devices. Here we describe an AlGaN multiple-quantum-well laser diode that emits light at 342 nm, the shortest wavelength ever reported for an electrically driven laser diode. To fabricate the laser, a low-dislocation-density AlGaN layer with an AlN mole fraction of 0.3 was grown on a sapphire substrate using a hetero facet-controlled epitaxial lateral overgrowth (hetero-FACELO) method1,2,3. An AlGaN multiple-quantum-well structure was then grown on the high-quality AlGaN layer. Lasing at a wavelength of 342.3 nm was observed under pulsed current mode at room temperature. Short-wavelength UV laser diodes are required for applications ranging from sensing, data storage and materials processing. Here, an electrically driven semiconductor laser that operates at 342.3 nm, the shortest wavelength so far, is reported. The device emits milliwatt-scale powers at room temperature when driven by pulsed current.

The influence of threading dislocation density on Hall effects in free‐standing GaN substrates

Free-standing GaN substrates are of great importance for short wavelength Laser Diodes (LDs) and high performance Light Emitting Diodes (LEDs) applications. One of the technical barriers for the applications is relatively high threading dislocation density (TDD) in GaN substrates known as non-radiative centers. In this paper, we analyzed the influence of TDD to Hall effects in Si-doped GaN free-standing substrates grown by Hydride Vapor Phase Epitaxy(HVPE). To verify the role of threading dislocations as deep acceptor level and carrier scattering lines, we compared active carrier concentration and Si doping concentration[nSi] of each GaN substrate with different DD. In addition, we measured O doping concentration[nO] of unintentionally doped(UID) GaN substrate that had similar DD with the Si-doped GaN substrate to consider the influence of doped O known as main background impurity, and compared the Hall characteristics of UID GaN with that of the Si-doped GaN. From the results, it was experimentally postulated that threading dislocations function as trap centers disturbing the movement of n-carriers in GaN substrates. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Single mode operation and extended scanning of anti-reflection coated visible laser diodes in a Littrow cavity

A method to increase the mode-hop-free tuning range is presented that is suitable for application with visible and short wavelength laser diodes, and relaxes the requirement on high tolerance mechanical components. Depending on the diode and cavity, the theory predicts an improvement of up to eight times the FSR of the extended cavity. In our system, an anti-reflection coated AlGaInP laser diode showed a mode-hop-free scan of 8 GHz, which is characteristic for the wavelength used in the device. Greater scanning ranges are predicted for shorter wavelength sources.

Ultraviolet InAlGaN multiple-quantum-well laser diodes

The Guest Editors of the Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5), Hiroshi Amano and Takashi Udagawa, have nominated the contributed presentation by Michael Kneissl et al. [1] as Editor's Choice of the present issue of physica status solidi (a). This paper is a report on ultraviolet InGaN, GaN and InAlGaN multiple-quantum-well (MQW) laser diodes with emission wavelengths between 368 and 378 nm, continuous-wave operation and a differential quantum efficiency of up to 4.2% which is remarkably high for these laser diodes grown directly on sapphire. The cover picture is a scheme of an InAlGaN MQW laser diode on sapphire substrate. Michael Kneissl is a Member of the Research Staff at the Palo Alto Research Center. He is responsible for device design, MOCVD growth, fabrication, and characterization of GaN-based short-wavelength laser diodes. The full Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5) are published in physica status solidi (c) – conferences and critical reviews, Vol. 0, No. 7 (November 2003) (ISBN 3-527-40489-9). Conference papers can also be found in phys. stat. sol. (b) 240, No. 2 (2003).

Spectroscopic imaging and the characterization of the autofluorescence properties of human bronchus tissues using uv laser diodes

Ultraviolet laser diodes (UV-LD) were used for the excitation source of autofluorescence (AF) measurements and spectroscopic imaging of the AF originating from the human bronchus was obtained. The AF spectra from normal bronchus tissues were measured and a clear AF spectrum was obtained by using a short wavelength (400 nm) laser diode; the overlap of the AF signal and excitation source could be substantially eliminated. In order to study the origin of AF intensity deterioration from bronchus tissue due to the formation of tumor tissues, the fluorescence spectrum was measured for various AF substances under various conditions. The blue AF signal of elastin and NADH solutions, which could not be easily studied by conventional excitation light sources, as well as the green AF became weak by adding lactic acid. The AF spectrum was measured for 512/spl times/512 pixels and the intensity mapping as a function of emission wavelength was obtained. Two-dimensional information of the AF signal intensity distribution for a certain wavelength component was measured. The feature originating from a region as small as about 100 /spl mu/m could be recognized. Numerical calculations of the data were performed and precise features of the AF were revealed.

Growth and optical characterization of large-scale crystal Cd xZn 1− xS whiskers via vapor reaction

Five kinds of large-scale Cd x Zn 1− x S whiskers (CWs) (10–300 μm in width and 2 μm in length) are successfully synthesized based on vapor reaction of (Cd+Zn) (g) and H 2S (g) and their PL spectra appear broad emission peaks that shift to short wavelength with increasing Zn 2+ in the ternary compound Cd x Zn 1− x S. The growth of the CWs is controlled by self-catalyzed vapor–liquid–solid and synthesis of CWs may open up a new possibility for the development of ideal materials for short wavelength laser diode applications.

Dual Layer Phase Change Optical Disk Using Limit Equalizer

A simple manufacturing process of multilayer recording disks has been developed to fabricate a large-capacity optical disk of more than 40 GB, using a short-wavelength laser diode and high numerical aperture (NA) objective lens. Some existing production facilities for the digital versatile discs (DVD) are applicable to this process. These disks can be utilized for long-time video recording of high-definition TV broadcasting. We have developed a dual-layer rewritable optical disk with capacity of more than 43 GB per one side of a 120 mm disk by this process. We obtained good performance of playback jitter for disks of 43 GB and 46.6 GB capacities with on-groove recording and limit equalizer at a user data transfer rate of 36 Mbps as well as good direct overwriting characteristics over 1,000 cycles.

Amplified luminescence and threshold current temperature dependencies of ZnSe and GaN laser diodes

Using a transfer equation approach, it is shown that the cavity-trapped amplified luminescence (AL) flux densities S integrated over the frequency and cavity length at the threshold of ZnSe, zinc-blende and wurtzite GaN laser diodes (LDs) with stripe-geometry bulk active layers reach (3.5–9)×104 MW/m2 within the temperature range 200–400 K. At these values of S, the nonlinear optical effects induced by AL can be observed. The AL induced recombination can enhance the threshold current density of the short wavelength LDs by two or even three times.

556 半導体レーザを用いた高精度光造形装置の開発

556 半導体レーザを用いた高精度光造形装置の開発

Radial and Tangential Tilt Detection for Rewritable Optical Disks

In an optical disk system which uses a short wavelength laser diode and a high numerical aperture objective lens, it is necessary to detect and compensate for the disk tilt, because the coma aberration deteriorates the read/write characteristics and the tilt margin becomes narrower. This paper presents a new radial and tangential tilt detection method for rewritable optical disks, which is based on the intensity distribution of the reflected light from the disk. This method features high sensitivity (about 0.37/° for radial direction and about 0.51/° for tangential direction) and is suitable for high-frequency servo operation. Moreover, it can be combined with the differential push-pull detection method and the land/groove detection method by using three beams. Experimental results have demonstrated the validity of this method.

Native defects and impurities in InN: First-principles studies using the local-density approximation and self-interaction and relaxation-corrected pseudopotentials

We perform first-principles density-functional calculations to investigate the electronic and atomic structure and formation energies of native defects and selected impurities ~O, Si, and Mg! in InN. For p-type material, the nitrogen vacancy has the lowest formation energy. In n-type material all defect formation energies are high. We discuss the effect of the band-gap underestimate in density functional theory ~DFT!, and compare the defect electronic structure obtained using DFT ~in the local-density approximation, LDA! with a recently developed self-interaction and relaxation-corrected ~SIRC! pseudopotential treatment. The SIRC calculations affect the positions of some of the defect states in the band gap, but the general conclusions obtained from the standard DFT-LDA calculations remain valid. Indium nitride is the least studied of the group-III-nitride materials, which are currently under intense investigation. Bulk InN is difficult to prepare due to its low thermal stability; 1 reliable experimental information about the properties of InN is therefore scarce. Indium-containing nitride alloys are an important constituent in devices: for example, the active layer in short-wavelength light-emitting diodes and laser diodes usually consists of In xGa12xN. Not intentionally doped InN has often been found to have very high electron densities—an observation similar to GaN before better doping control of that material was achieved. The unintentional n-type conductivity of InN has been attributed to the nitrogen vacancy (VN) or to the nitrogen antisite. 2 In order to control the material properties and ultimately the device characteristics, an understanding of native defects and impurities in the III nitrides and their alloys is essential. The calculations reported here show that neither vacancies nor antisites can explain the observed n-type conductivity of InN. We have therefore examined oxygen and silicon impurities, finding that they act as donors and that they can easily be incorporated during growth. First-principles calculations based on density functional theory ~DFT! within the local density approximation ~LDA! have produced important information about defects and impurities in semiconductors in general, and the nitrides in particular. 3,4 It is well known, however, that DFT-LDA produces band gaps significantly smaller than experiment. 5 Defects can introduce levels in the band gap; when these levels are occupied with electrons, they contribute to the total energy of the system. If the energetic position of the defect levels is incorrect due to the band-gap error, the resulting total energy may also be affected. The band-gap error results largely from a discontinuity in the exchange-correlation potential upon addition of an extra electron. 6 This discontinuity is inherent to the Kohn-Sham treatment of DFT; indeed, we have found that use of the generalized gradient approximation ~GGA! offers no improvement over LDA with respect to the band-gap problem. 7

Short-wavelength laser diodes based on AlInAs/AlGaAs self-assembled quantum dots

Self-assembled quantum dots (QDs) of highly strained InAlAs have been grown by molecular beam epitaxy in separate-confinement p–i–n heterostructures on (001) GaAs substrates. Results from a systematic study of samples with varying amounts of deposited material relates the observed emission peaks with QD levels, wetting layer states, or barrier materials. For samples with high-QD concentration, lasing is observed in the upper-QD shells. A sample with contact layers improving carrier and optical confinement operates up to room temperature and displays lowered threshold current densities. A threshold current density of ∼4 A/cm2 is measured for this structure at T=5 K and continuous-wave operation is obtained up to T∼77 K. A material gain larger than 1.7×104 cm−1 is measured for this single-layer structure. Lasing is observed in the upper-QD shells for small gain media, and progresses towards the QD lower states for longer cavity lengths representing an emission shift of 45 meV. A minor dependence of the threshold on QD density is found for samples having densities between 20 and hundreds of QDs per micron squared. For samples with multiple QD layers displaying vertical self-assembling, an increase in the emission linewidth is observed compared with single-layer samples and multilayer samples with uncorrelated growth.