Showing papers by "Kenichi Iga published in 1996"
TL;DR: In this paper, a short-cavity laser with deep-grating distributed Bragg reflectors (DBRs) was proposed, which achieved high reflectivity over 97% even with three periods of grating.
Abstract: We have proposed a novel short-cavity laser with deep-grating distributed Bragg reflectors (DBRs). We monolithically fabricated a 0.98 µm InGaAs/AlGaAs device and 1.55 µm GaInAsP/InP device using electron beam lithography and a reactive ion beam etching technique. The lasing operation of both devices was achieved at room temperature. From a comparison of the threshold current from the experimental result with that from the theoretical result, the reflectivity of formed DBRs was estimated to be less than 30%. The theory also predicts that the ideal DBR exhibits a high reflectivity over 97% even with 3 periods of grating. It achieves lasing operation with a threshold current less than 100 µA using a cavity shorter than 10 µm. This high performance is realized by reducing the surface roughness and damage to etched sidewalls and improving the reflectivity of the DBR.
102 citations
TL;DR: In this paper, an InGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) was fabricated on a GaAs(311)A substrate by molecular beam epitaxy (MBE) and demonstrated continuous wave operation at room temperature.
Abstract: We have fabricated an InGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs(311)A substrate by molecular beam epitaxy (MBE) and demonstrated continuous wave operation at room temperature. A threshold current density of 80 A/cm/sup 2//well and very stable polarization characteristics up to 2.7 times the threshold were achieved. The polarization state with the highest optical intensity was oriented along the [2~33] direction, which is the crystallographic axis exhibiting the maximum gain. An extinction ratio of more than 12.7 dB was obtained between two orthogonal polarization states. The high and anisotropic gain of a (311)A-oriented VCSEL will drastically improve the device performance by optimization and process engineering.
56 citations
TL;DR: In this paper, the photon recycling effect in light emitting devices was estimated theoretically and experimentally, and it was shown from the rate equation analysis that this effect is marked when the injection carrier density is lower than 1×1018 cm-3 and the factor given by the average photon lifetime of spontaneous emission multiplied by the optical confinement factor inside the active region is larger than 100 fs.
Abstract: The photon recycling effect in light emitting devices was estimated theoretically and experimentally. It was shown from the rate equation analysis that this effect is marked when the injection carrier density is lower than 1×1018 cm-3 and the factor given by the average photon lifetime of spontaneous emission multiplied by the optical confinement factor inside the active region is larger than 100 fs. The external efficiency in light emitting diodes (LEDs) is improved by one order of magnitude if this factor is increased to 1 ps by the strong optical confinement around the active region. This theoretical estimation well agreed with the experimental result in fabricated GaInAsP/InP LEDs having a relatively wide emitting layer and a metal mirror; the efficiency became 1.6–1.8 times higher when the factor for fabricated LEDs was longer than 100 fs. An LED that exhibits a high efficiency comparable to those of laser diodes will be realized by improving the reflectivity of the metal mirror to higher than 99%.
33 citations
Patent•
04 Jun 1996
TL;DR: In this article, an optical apparatus for controlling an angle of divergence of a ring beam which is capable of irradiating a ringed light beam having a uniform distribution of light intensity with an arbitrary angle with respect to the optical axis in the direction of 360° concurrently is presented.
Abstract: An optical apparatus for controlling an angle of divergence of a ring beam which is capable of irradiating a ringed light beam having a uniform distribution of light intensity with an arbitrary angle of divergence with respect to the optical axis in the direction of 360° concurrently. The optical apparatus comprises parallel beam generating means (2) to which a light beam (L1) output from a light source (1) is input and which outputs the incident light (L2) by transforming it into a parallel light beam (L3); ring beam generating means (3) to which the parallel beam (L3) output from the parallel beam generating means (2) is input and which outputs the input light (L4) by transforming it into a ringed light beam (L5) whose shape is annular when irradiated to an imaginary plane perpendicular to an optical axis (A--A); and divergent angle changing means (4) for changing an angle of divergence (θ3) (an angle formed between the optical axis (A--A) and the direction of propagation of the ring beam (L5)).
25 citations
TL;DR: In this paper, high-quality crystals for VCSEL structures on (311)A having flat and smooth heterointerfaces were obtained by optimizing the growth conditions, and it was experimentally demonstrated that the optical anisotropic gain of (311)-oriented strained-layer quantum wells is effective for polarization control.
Abstract: We have fabricated InGaAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) grown on GaAs(311)A substrates by molecular beam epitaxy. High-quality crystals for VCSEL structures on (311)A having flat and smooth heterointerfaces were obtained by optimizing the growth conditions. It was experimentally demonstrated that the optical anisotropic gain of (311)-oriented strained-layer quantum wells is effective for polarization control. A [*BAR*2*BAR*33] polarization mode is stable against the injection currents of 3 times the threshold. In addition, the threshold current density of 80 A/(cm2well) is achieved for a device with a laser aperture as large as 25 µ m square, which is comparable to or even lower than that of (100)-oriented VCSELs.
24 citations
TL;DR: In this article, a dry etch technique using Cl2 based reactive ion beam etching (RIBE) has been developedd for GaN-based semiconductor lasers The etching rate of 350 − 1000 A/min was obtained This is applicable for micro fabrication of GaN based materials in the same way as used for other III-V group semiconductors.
Abstract: A dry etch technique using Cl2 based reactive ion beam etching (RIBE) has been developd for GaN-based semiconductor lasers The etching rate of 350 − 1000 A/min was obtained This is applicable for micro fabrication of GaN based materials in the same way as used for other III-V group semiconductors Furthermore, it is found that the surface damage of GaN layers induced by the RIBE-etch can be removed using ultra-violet assisted wet-etching using alkali solution The PL intensity of damaged GaN layers is increased after the post-process wet-etching
16 citations
21 Apr 1996
TL;DR: In this paper, the progress of surface emitting laser ranging from 1.55 to 0.4 /spl mu/m by considering materials and performance, including threshold, power output, polarization, RIN, linewidth, spontaneous emission control, and photon recycling is discussed.
Abstract: The author reviews the progress of surface emitting lasers ranging from 1.55 to 0.4 /spl mu/m by considering materials and performance, including threshold, power output, polarization, RIN, linewidth, spontaneous emission control, and photon recycling. Some possible applications are discussed.
13 citations
TL;DR: In this paper, the average hole concentration in the ZnSe : (Li, N) layer formed at a diffusion temperature of 470° C was as high as 1×1018 cm-3, and the layer exhibited a resistivity of ρ=0.3 Ω cm and a hole mobility of µ p=18 cm2/Vs.
Abstract: We have achieved high concentration p-type doping of ZnSe grown by metalorganic vapor phase epitaxy using a Li3N diffusion technique. The average hole concentration in the ZnSe : (Li, N) layer formed at a diffusion temperature of 470° C was as high as 1×1018 cm-3, and the layer exhibited a resistivity of ρ=0.3 Ω cm and a hole mobility of µ p=18 cm2/Vs.
8 citations
TL;DR: In this article, the threshold current density of GaN-based VCSELs has been estimated and the introduction of a quantum well structure as an active layer is very effective for a low threshold operation.
Abstract: The threshold current density of GaN-based vertical cavity surface emitting lasers (VCSELs) has been estimated. It is clarified that the introduction of a quantum well structure as an active layer is very effective for a low threshold operation and that high reflective mirrors are required for low threshold GaN-based VCSELs. Also, attempts on micro-fabrication process of GaN is presented.
6 citations
TL;DR: In this paper, a basic design and fabrication of InGaAs/GaAs quantum wires (QWRs) is discussed for the purpose of realizing vertical-cavity surface-emitting lasers (VCSELs) for low-threshold operations and a threshold current density of 100 A/cm2 is obtained.
Abstract: A basic design and fabrication of InGaAs/GaAs quantum wires (QWRs) is discussed for the purpose of realizing vertical-cavity surface-emitting lasers (VCSELs) A structure of QWR VCSELs is presented for low-threshold operations and a threshold current density of 100 A/cm2 is obtained A novel method for fabricating densely packed QWRs on V-grooved substrates is demonstrated by using low-pressure metalorganic chemical vapor deposition Polarization anisotropy was observed by both photoluminescence and current injection measurements
Patent•
04 Jun 1996
TL;DR: In this paper, the authors present an optical apparatus for controlling an angle of divergence of a ring beam which is capable of irradiating a ringed light beam having a uniform distribution of light intensity with an arbitrary angles of divergence with respect to the optical axis in the direction of 360° concurrently.
Abstract: An optical apparatus for controlling an angle of divergence of a ring beam which is capable of irradiating a ringed light beam having a uniform distribution of light intensity with an arbitrary angle of divergence with respect to the optical axis in the direction of 360° concurrently. The optical apparatus comprises parallel beam generating means (2) to which a light beam (L1) output from a light source (1) is input and which outputs the incident light (L2) by transforming into a parallel light beam (L3); ring beam generating means (3) to which the parallel beam (L3) output from the parallel beam generating means (2) is input and which outputs the input light (L4) by transforming into a ringed light beam (L5) whose shape is annular when irradiated to an imaginary plane vertical to an optical axis (A-A); and divergent angle changing means (4) for changing an angle of divergence (an angle formed between the optical axis (A-A) and the direction of propagation of the ring beam (L5)) (θ3) of the ring beam (L5) output from the ring beam generating means (3) on the way.
TL;DR: In this paper, electron beam evaporation and laser ablation molecular beam epitaxy (MBE) were used as buffer layers to grow GaN by metal organic vapor phase epitaxy.
Abstract: ZnO layers have been deposited by electron beam (EB) evaporation and laser ablation molecular beam epitaxy (MBE) as buffer layers to grow GaN by metal organic vapor phase epitaxy (MOVPE). The photoluminescence spectrum of the ZnO layer deposited by an EB evaporator shows an emission peaks of 367 nm. GaN was grown on ZnO/Si, Si and sapphire substrates under the same growth condition employing low-temperature-grown AIN buffers to prevent the dissociation of ZnO during the high GaN growth. The GaN on ZnO/Si shows sharp photoluminescence spectra at room temperature and 10 K. These results indicate a potential use of ZnO/Si substrates for GaN based blue-UV optical devices such as vertical-cavity surface-emitting lasers (VCSELs).
TL;DR: In this paper, the threshold current density for vertical cavity surface emitting lasers consisting of a 520 nm emitting ZnCdSe active layer, by taking account of optical gain as a function of bandgap energy and spontaneous lifetime, is estimated.
Proceedings Article•
02 Jun 1996TL;DR: In this article, an n-type modulation-doped quantum well (QW) was used to achieve a reduction in threshold current in InGaAs-AlGaAs QW lasers.
Abstract: Summary form only given. It is expected that an n-type modulation-doped quantum well (QW) lasers can achieve a reduction in threshold current. In this report, we have demonstrated strained InGaAs-AlGaAs QW lasers employing the n-type modulation doping for reducing threshold current for the first time. The active region of QW lasers was grown by a low pressure metal organic chemical vapor deposition.
TL;DR: In this article, a GaInAs-GaAs quantum well laser with a 1/spl times/20 power splitter inside the laser cavity was proposed, which enhances light-wave diffraction in a planar free-space region.
Abstract: The authors propose a miniature semiconductor optical power splitter with a submicrometre wide input aperture enhancing lightwave diffraction in a planar free-space region. They present its design and have demonstrated a GaInAs-GaAs quantum well laser with a miniature 1/spl times/20 power splitter inside the laser cavity.
05 Aug 1996
TL;DR: In this paper, a self-consistent model was proposed to estimate the carrier diffusion length in VCSELs with an oxide confinement structure, taking into account carrier diffusion as well as various optical processes like scattering or diffraction.
Abstract: Recently, the threshold of 980 nm VCSELs with an oxide confinement structure has been reduced below 100 /spl mu/A. We model their ultimate threshold performance as well as secondary mode discrimination, and estimate the carrier diffusion length in our devices. The self-consistent model takes into account carrier diffusion as well as various optical processes like scattering or diffraction, and uses a logarithmic gain model for quantum wells. The active layer consists of three 80 /spl Aring/ thick InGaAs strained quantum wells separated by 100 /spl Aring/ GaAs barriers.
01 Jan 1996
TL;DR: A detailed description of the equipment necessary for LPE and the epitaxial techniques required for double heterostructures can be found in this article, where the authors also discuss the advantages of LPE.
Abstract: Liquid-Phase Epitaxy (LPE) has many advantages and is capable of producing reliable semiconductor devices. This chapter provides a detailed description of the equipment necessary for LPE and the epitaxial techniques required for double heterostructures. As discussed in Chap. 4, the principle behind LPE is very simple: epitaxial layers can be thermodynamically grown on a substrate with the same orientation when the substrate meets the oversaturated solution. Since semiconductor-laser research began, LPE has been a popular growth technique and it still plays an important role in producing semiconductor lasers, light emitting diodes and photodetectors.
TL;DR: In this paper, a low threshold vertical-cavity surface-emitting laser (VCSEL) was constructed by a native oxidation technique and the strong optical and electrical confinements enabled to achieve low thresholds.
Abstract: In order to realize a low threshold vertical-cavity surface-emitting laser (VCSEL), we have fabricated a micro-cavity structure by a native oxidation technique. The strong optical and electrical confinements enabled to achieve low thresholds. For further threshold reduction, we have demonstrated an n-type modulation doped quantum well (QW) laser and a 30% reduction of threshold in n-type doped QW laser compared with undoped QW lasers is observed. These are the first experiments for InGaAs/AlGaAs materials.
TL;DR: In this paper, the authors have shown that there is no significant residual stress to the active region originating from the AlAs oxide layer in VCSELs, and that the residual stress is negligible.
Abstract: The stress effect of an AlAs oxide layer which is formed near the active region to confine carriers in vertical-cavity surface-emitting lasers (VCSELs) has been discussed. From the result of micro-photoluminescence measurement, it has been shown that there is no significant residual stress to the active region originating from the AlAs oxide layer.
Patent•
04 Jun 1996
01 Jan 1996
TL;DR: The Liquid-Phase Epitaxy (LPE) growth technique is based on simple principles and resrs upon simple apparatuses as discussed by the authors, and it is described in Chap. 5.
Abstract: The Liquid-Phase Epitaxy (LPE) growth technique is based on simple principles and resrs upon simple apparatuses. It is described in Chap. 5. Recently, superlattice devices composed of finer heterostructures have attracted the attention of device researchers because the quantum effects can drastically improve the device characteristics. Fine-structured epitaxy for producing superlattice devices requires thickness controllability of less than several hundred A, uniformity and heterointerface abruptness. Vapor phase and beam epitaxial growth techniques for fine-structured devices are being intensely studied. This chapter introduces and explains Metal-Organic Chemical Vapor Deposition (MOCVD) and Chemical-Beam Epitaxy (CBE).
01 Jan 1996
TL;DR: In this article, the most basic, necessary condition required of laser materials is, of course, that the input energy can be converted into light energy with a reasonably high efficiency, and the injected electron and hole concentrations should be higher than approximately 2 · 1018 cm-3, so that direct recombination can occur and optical gain is sufficient to reach the lasing threshold.
Abstract: Compound semiconductors, especially III-V compound semiconductors, are well suited for semiconductor lasers. The most basic, necessary condition required of laser materials is, of course, that the input energy can be converted into light energy with a reasonably high efficiency. In addition to this, the injected electron and hole concentrations should be higher than approximately 2 · 1018 cm-3, so that direct recombination can occur and optical gain is sufficient to reach the lasing threshold. Materials research is important, with the goal of finding materials capable for producing various semiconductor lasers with a wide range of lasing wavelengths. In Chap.2 we concentrate on investigating material properties which determine the aforementioned basic characteristics of semiconductor lasers.
01 Jan 1996
TL;DR: In this paper, the authors used an index waveguide structure to stabilize the transverse and longitudinal modes of semiconductor laser devices, which is achieved by using a grating structure created by overgrowth epitaxy.
Abstract: It is very important for semiconductor lasers to have stable transverse and longitudinal modes in order to obtain reliable performance. This is achieved by using an index waveguide structure. One of the most common techniques to control the longitudinal mode is to equip the inside of the device with a grating structure, created by overgrowth epitaxy. The LPE growth technique is the most suitable for this purpose. This is partly due to the phenomenon that LPE tends to flatten the surface, which is remarkable in comparison with other epitaxial growth techniques. This feature greatly helps in the fabrication of transverse-mode-controlled structures such as V-groove structures, buried heterostructures, Distributed FeedBack (DFB) and Distributed Bragg Reflector (DBR) structures. The theory behind stabilizing transverse and longitudinal modes and its importance will be explained. Next, structured epitaxial techniques will be summarized in Sects.9.3–6, and the fabrication of multilayer structures will be described in Sects.9.7 and 8.
TL;DR: In this paper, a fitting method for obtaining a functional form of the refractive index profile of planar microlenses made by ion exchange techniques from total shearing interferometric measurements is presented.
Abstract: We present a fitting method for obtaining a functional form of the refractive index profile of planar microlenses made by ion exchange techniques from total shearing interferometric measurements. Compared to the usual power series expansion fit, this method allows a reduction in the number of coefficients needed to characterize a lens.
01 Jan 1996
TL;DR: In this paper, the fundamental concepts of the epitaxial growth of III-V compound semiconductors are summarized and compared with other crystal-growth techniques, such as metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and Chemical Beam Epitaxy (CBE), among others.
Abstract: This chapter summarizes the fundamental concepts of the epitaxial growth of III–V compound semiconductors. The relevant crystal-growth technologies encompass two categories: bulk crystal preparation for a substrate to be used as a seed, and thin-film epitaxial growth. Later chapters will contain detailed discussion of the epitaxial-growth techniques, and here we overview several characteristics of liquid-phase epitaxy by comparing them with other crystal-growth techniques, such as Metalorganic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), and Chemical Beam Epitaxy (CBE), among others.
01 Jan 1996
TL;DR: In this article, the fabrication of actual laser devices and the relevant characterization techniques are examined and the design criteria stated in Chap. 3 should be checked as the first step of device evaluation.
Abstract: In this chapter, we examine the fabrication of actual laser devices and the relevant characterization techniques. The design criteria stated in Chap. 3 should be checked as the first step of device evaluation. Measurement of fundamental laser parameters such as voltage/current curves, threshold current density and spectral characteristics describe the important material properties of grown wafers. The measurement results also provide useful feedback for subsequent epitaxial growths.
21 Apr 1996
TL;DR: In this paper, a strain-balanced InAsP/InP/GaInP short-period superlattice with period of 15 monolayer with 2% compressive well and 2% tensile barrier strain has been grown by CBE with 1 monollayer InP as intermediate layer.
Abstract: A strain-balanced InAsP/InP/GaInP short-period superlattice with period of 15 monolayer with 2% compressive well and 2% tensile barrier strain has been grown by CBE with 1 monolayer InP as intermediate layer. A superlattice with uninterrupted flow of TMIn and PH/sub 3/ at the well-barrier interfaces gave the best results. When the superlattice is grown at the p-side of an InP p-n homojunction, the turn-on voltage due to the superlattice was 0.3 V. It has been estimated that a laser diode loaded with such a superlattice at the p-side should have an operating current density not more than 3.3 kA/cm/sup 2/.