Dependence of differential quantum efficiency on the confinementstructure in InGaAs/InGaAsP strained-layer multiple quantum-well lasers

An internal efficiency of 91% was obtained with In_0.7Ga _0.3As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 μm. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP (λ=1.3 μm) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency     

Low-threshold InGaAsP/InGaP lasers at 810 nm grown on GaAs substrate by LPE

InGaAsP/InGaP double-heterostructure lasers emitting at 810 nm have been fabricated on GaAs substrates using liquid-phase epitaxy (LPE). A threshold current as low as 2.0 kA/cm2 with an external differential quantum efficiency of 54% is obtained. Thus it has been shown that high-quality InGaAsP/InGaP lasers can be obtained by LPE growth.     

980-nm aluminum-free InGaAs/InGaAsP/InGaP GRIN-SCH SL-QW lasers

The design of 980-nm InGaAs/InGaAsP/InGaP GRIN-SCH lasers with aluminium-free GaAs-based materials is discussed. The first approach was successful MOCVD growth of InGaAsP alloy lattice matched to GaAs. It was found that an immiscible region existed, as determined by photoluminescence measurements. The main approach was to introduce the graded bandgap structure consisting of InGaAsP layers lattice matched to GaAs into GaAs/InGaP interfaces. The graded structure suppresses the heterojunction spikes, especially of the valence band at these interfaces. As a result, series resistance of GRIN-SCH lasers with the graded bandgap structure was reduced compared with simple SCH lasers with abrupt bandgap interfaces due to improved hole injection. Furthermore, the optimum graded structures for optical confinement region were investigated to improve the carrier injection efficiency, especially electron injection efficiency into a single quantum well active layer. Also, this graded bandgap structure formed the graded refractive index profile in an active region, which is the so-called GRIN-SCH waveguide. The GRIN-SCH profile could be controlled to narrow the transverse beam divergence for high coupling efficiency into a single-mode fiber and to reduce the optical power density at facets for high reliability. Finally the results of a life-test of GRIN-SCH lasers was shown, and the lifetime of GRIN-SCH lasers with immiscible InGaAsP layers was discussed     

Measurement of radiative and nonradiative recombination rates in InGaAsP and AlGaAs light sources

A small signal method is used to measure the carrier lifetime as a function of injected carrier density, and the results are used to determine the radiative and nonradiative recombination rates for AlGaAs LED's and 1.3 μm InGaAsP lasers. For AlGaAs LED's the radiative recombination constant decreases with injected carrier density and the rate equation contains a small nonradiative Cn³term. The low internal efficiency of 1.3 μm InGaAsP lasers is found to be primarily caused by two factors: a radiative coefficientB(n)which strongly decreases with the injected carrier density, and CHHS Auger recombination having a recombination coefficient of1-2 times 10^{-29}cm⁶/s. A recombination term representing carrier leakage is observed in some devices, but it is not the principal cause of low internal efficiency.     

Tensile-strained GaAsP/GaInAsP/GaInP quantum well lasers

Tensile-strained GaAsP/GaInAsP/GaInP separate-confinement-heterostructure single-quantum-well (SCH-SQW) lasers are reported for the first time. A low threshold current density of 261 A/cm² and a high characteristic temperature of 190 K were obtained for a 1600-μm long broad-area laser having ~0.3% lattice strain. The internal quantum efficiency was as high as 93% and internal waveguide loss 3.3 cm^-1. Some primary results of unstrained GaAs/GaInAsP and compressive-strained (1.4%) InGaAs/GaInAsP SCH-SQW lasers are also presented. Both the tensile and compressive-strained lasers exhibited higher quantum efficiency than the unstrained lasers. On the other hand, the tensile-strained lasers had nearly the same internal waveguide loss and threshold current as the unstrained lasers     

High power and high efficiency operation of Al-freeInGaAs/GaInAsP/GaInP GRINSCH SQW lasers (λ≃0.98 μm)

High power and high quantum efficiency Al-free InGaAs/GaInAsP/GaInP GRINSCH SQW lasers emitting at 0.98 μm are reported. A CW output power as high as 580 mW and single lateral mode power up to 280 mW were achieved for the Al-free ridge waveguide lasers at room temperature. The lasers exhibited a high internal quantum efficiency of 99% and low internal waveguide loss of 3.2 cm^-1. A high characteristic temperature of 217 K and low threshold current density of 109 A/cm² were also obtained. The results are the best obtained for Al-free 0.98 μm pumping lasers     

Compensation of internal thermal stresses in InGaAsP/InP lasers for polarization stabilization

Internal thermal stresses in the active layer of a conventional InGaAsP/InP laser may cause polarization instabilities which normally do not exist in conventional AlGaAs/GaAs lasers. We analyze a structure with a buffer layer for Polarization stabilization by compensation of the internal thermal stresses in InGaAsP/InP lasers. Stress analyses are carried out for various structures to obtain the conditions for optimal stress-free structures. The effects of stresses from external sources are also discussed.     

Temperature dependence of light-current characteristics of0.98-μm Al-free strained-quantum-well lasers

The decrease of the differential efficiency of 0.98-μm semiconductor lasers with temperature can make high power, high temperature applications difficult. We present an experimental and theoretical study of the temperature dependence of the internal quantum efficiency, internal loss and differential gain of 0.98-μm InGaAs/InGaAsP/InGaP strained quantum well lasers. In contrast to some earlier results, our measurements show the dominance of internal loss, attributed to free carrier absorption, in determining the temperature dependence of the differential efficiency, and show that leakage current is negligible below 120°C     

High temperature 10 Gbit/s directly modulated 1.3 μm DFB lasersusing InAsP/InGaAsP materials

Uncooled 10 Gbit/s direct modulation of high-power 1.3 μm InAsP/InGaAsP directly modulated multiple quantum well distributed feedback (DFB) lasers is demonstrated. High resonant frequencies and high efficiency at 85°C are obtained due to the high epitaxial quality of ternary, aluminium-free, quantum wells. Floor-free transmission on 90 and 140 ps/nm within ITU recommendations are demonstrated     

Facet oxidation of InGaAsP/InP and InGaAs/InP lasers

The facet oxidation of InGaAsP/InP and InGaAs/InP lasers is investigated after aging under high constant optical output power or high current stress. Facet oxidation in InGaAsP/InP lasers is negligibly small under several thousand hours of practical operation. The thickness of oxide film increases in proportion to optical output power and logarithm of aging time. The growth rate of facet oxide film weakly depends on the junction temperature and the activation energy is estimated to be 0.07 eV within a experimental range between 25 and 150°C. The facet of InGaAs/InP lasers are oxidized more easily than that of InGaAsP/InP lasers but are about two orders of magnitude more stable against oxidation than that of AlGaAs/GaAs lasers.     

Enhanced relaxation oscillation frequency and reduced nonlinear K-factor in InGaAs/InGaAsP MQW lambda /4-shifted DFB lasers

The relaxation oscillation frequency, f/sub r/, of 1.55 mu m InGaAs/InGaAsP MQW lambda /4-shifted DFB lasers was doubled by increasing the carrier injection efficiency into each quantum well, which results from an optimised bandgap energy and optimised thickness of the barrier layers. The nonlinear K-factor which determines the maximum modulation bandwidth through the damping phenomenon can be reduced by adopting a p-type modulation doped MQW structure in the active layer.<>     

1 W fibre coupled power InGaAsP/InP 14xx pump laser for Raman amplification

A 1 W record singlemode fibre coupled output power using 1460 nm InGaAsP/InP non-tapered buried ridge lasers has been demonstrated. The impact of the bandgap of the passive quaternary waveguide on internal loss was investigated. Optimised design allows internal losses as low as 3.3 cm/sup -1/, external efficiency of 0.46 W/A for a 3 mm-long laser and symmetrical (12/spl deg//spl times/12/spl deg/) far-field pattern.     

Analysis of electrical, threshold, and temperature characteristics of InGaAsP/InP double- heterojunction lasers

This paper presents an extensive study of the fundamental characteristics of InGaAsP/InP double-heterojunction (DH) lasers with a wavelength of 1.3 μm. The confinement properties of injected carriers in the quaternary active region, the electrical properties such as leakage current and diode current versus voltage, the threshold characteristics, and the threshold temperature characteristics are determined through an analysis of the heterojunction energy band structure. The threshold temperature characteristics and the carrier leakage from the active region into the confining layers are examined in detail. To clarify the dependence of carrier leakage on lasing wavelength in InGaAsP/InP DH lasers and to explain the difference between GaAlAs/GaAs DH and InGaAsP/InP DH lasers, the barrier heights required to effectively confine the injected carriers and the effective carrier masses in the active region are discussed. Various possible explanations for the observed threshold temperature characteristics are considered.     

High-speed InGaAsP/InP multiple-quantum-well laser

The authors describe practical high-speed InGaAsP/InP lasers based on compressively strained quantum wells. Buried heterostructure lasers with threshold currents of 10 mA and slope efficiencies of 0.23 mW/mA are used. A modulation bandwidth of 20 GHz is obtained at a low drive current of 90 mA. A K factor of 0.25 ns is obtained and the intrinsic bandwidth of these lasers is estimated at 35 GHz     

Characteristics of diffused-stripe InP/InGaAsP/InP lasers emitting around 1.55 µm

Fabrication and lasing characteristics of InGaAsP/InP lasers emitting around 1.55 μm are described. Zn-diffused stripe-geometry lasers with emission wavelengths in the1.53-1.60mum range were fabricated from InP/InGaAsP/InP DH epitaxial wafers prepared by a low temperature LPE technique. The dependence of the lasing charaeteristics on the stripe width was examined. The lowest threshold current (≃160 mA under CW operation at 27°C) was obtained for a laser with a 13 μm stripe. CW operation of the laser has been achieved at a heat-sink temperature as high as 53°C. For sufficiently narrow stripe widths (simeq6 mum), fundamental-transverse mode and single-longitudinal mode operation was obtained under CW operation. Moreover, the lasers have good high-frequency performance. The lasers showed excellent dynamic properties without waveform distortion under high-frequency (800 Mbits/s) large-signal pulse modulation. The full width at half maximum of the longitudinal mode envelope was approximately 30 Å at 800 Mbits/s.     

Very-low-threshold, highly efficient, and low-chirp 1.55-/spl mu/m complex-coupled DFB lasers with a current-blocking grating

Low-threshold current DFB lasers have been fabricated based on a complex-coupled structure with a current blocking grating. A threshold current as low as 5 mA was obtained, which enabled high temperature operation up to 105/spl deg/C. Asymmetric facet coatings were applied to obtain a high efficiency of 0.3 W/A. The strained InGaAsP MQW active region and the antiphase coupling has resulted in a low modulation chirping. By direct modulation of the device at 2.488 Gb/s and using optical amplifiers, we have demonstrated digital transmission over a 235 km-long standard single-mode fiber with a power penalty of 1.55 dB.     

High temperature characteristics of strained InGaAs/lnGaAsP quantumwell lasers lattice matched to GaAs

The effect of high temperature on the threshold current density and the gain of In_xGa_1-xAs/InGaAsP (E_g=1.6 eV) QW lasers lattice matched to GaAs is investigated theoretically. These results are also compared with those of In_x Ga_1-xAs/GaAs QW lasers. It is found that better performance can be achieved in InGaAs/InGaAsP lasers compared to InGaAs/GaAs lasers at high temperature. This is due to the fact that the temperature dependence of the threshold carrier density for InGaAs/InGaAsP lasers is weaker than that for InGaAs/GaAs lasers. The calculated characteristic temperature is in good agreement with reported experimental results     

The effect of barrier composition on the vertical carrier transport and lasing properties of 1.55-/spl mu/m multiple quantum-well structures

In this paper, the effect of barrier bandgap and composition on the optical performance of 1.55-/spl mu/m InGaAsP/InGaAsP and InGaAsP/InGaAlAs multiple quantum-well structures and Fabry-Perot lasers is evaluated experimentally. Direct vertical carrier transport measurements were performed through strain-compensated multiple quantum-well (MQW) test structures using femto-second laser pulse excitation and time-resolved photoluminescence up-conversion method. MQW test structures were grown with different barrier composition (InGaAsP and InGaAlAs) and barrier bandgap (varied from /spl lambda//sub g/= 1440 to 1260 nm) having different conduction band /spl Delta/E/sub c/ and valence band discontinuity /spl Delta/E/sub v/, while keeping the same InGaAsP well composition for all the structures. The ambipolar carrier transport was found to be faster in the structures with lower valence band discontinuity /spl Delta/E/sub v/. Regrown semi-insulating buried heterostructure Fabry-Perot (SIBH-FP) lasers were fabricated from similar QWs and their static light-current-voltage characteristics (including optical gain and chirp spectra below threshold) and thermal characteristics were measured. Lasers with InGaAlAs barrier showed improved high-temperature operation, higher optical gain, higher differential gain, and lower chirp, making them suitable candidates for high-bandwidth directly modulated uncooled laser applications.     

Barrier composition dependence of differential gain and externaldifferential quantum efficiency in 1.3-μm strained-layermultiquantum-well lasers

Dependence of the differential gain and the external differential quantum efficiency on the composition of InGaAsP barrier layers were investigated for 1.3 μm InGaAsP-InGaAsP compressively strained layer (SL) multiquantum well (MQW) lasers. In this investigation, we compared between SL-MQW lasers and unstrained MQW lasers having the same well thicknesses and the same emitting wavelength in order to clarify the effect of strain for each barrier composition. As a result It has been found that the barrier composition has large influence on the differential gain and the external differential quantum efficiency in the SL-MQW lasers. Narrower band-gap barrier means little effect of strain on the differential gain due to the electron overflow from a well layer, while wider band-gap barrier means degradation in the differential gain and the external differential quantum efficiency due to the nonuniform injection of hole into a well layer. In this experiment, the barrier composition of 1.05 μm is suitable for 1.3 μm InGaAsP-InGaAsP SL-MQW lasers to realize large differential gain and high external differential quantum efficiency simultaneously     

High-performance 980-nm quantum-well lasers using a hybrid materialsystem of an Al-free InGaAs-InGaAsP active region and AlGaAs claddinglayers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm² (at a cavity length of 1500 μm), internal quantum efficiency of ~95%, and low internal loss of 1.8 cm^-1. Both broad-area and ridge-waveguide laser devices are fabricated. For 100-μm-wide stripe lasers with a cavity length of 800 μm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T₀) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-μm-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A