High-power 1.5 mu m all-MOVPE buried heterostructure graded index separate confinement multiple quantum well lasers

A maximum total CW output power of 190 mW has been obtained at 1.55 mu m using a buried heterostructure graded index separate confinement multiple quantum well laser grown entirely by metalorganic vapour-phase epitaxy.<>     

Lifetime broadening in GaAs-AlGaAs quantum well lasers

Experimental observations of spontaneous emission spectra from GaAs-AlGaAs quantum well lasers shown that spectral broadening should be included in any realistic model of laser performance. A model of the lifetime broadening due to intraband Auger processes of the Landsberg type is described and developed for the case of electron-electron scattering in a 2-D system. The model is applied to the calculation of gain and spontaneous emission spectra and gain-current relationships in short-wavelength GaAs-AlGaAs quantum well lasers, and the results are compared with those obtained using both a fixed intraband scattering time and one that varies as n^-1/2, where n is the volume injected carrier density     

Effect of cladding layer thickness on the performance ofGaAs-AlGaAs graded index separate confinement heterostructure singlequantum-well lasers

The thinning of cladding layers of GaAs-AlGaAs graded index separate confinement heterostructure single quantum-well (GRINSCH-SQW) lasers offers several advantages. These advantages include easier fabrication of surface grating-based lasers and ridge lasers, the reduction of growth time and source-material use, and the more effective removal of heat due to lower thermal resistance. Experimental results from GRINSCH-SQW lasers showing that typical cladding thicknesses of 1.5 to 2 μm are much thicker than necessary are presented. Lasers with cladding layers as thin as 4500 Å have not shown any increase in threshold current. Theoretical analysis shows good agreement with the experimental results on the minimum cladding thickness necessary to prevent an increase in the threshold current. The differential quantum efficiency is theoretically considered and is found to be more sensitive to cladding-layer thickness     

AlGaInP/GaInAs strained quantum well lasers

AlGaInP cladding layers have been applied for the first time to GaInAs strained quantum well lasers oscillating around 0.98 mu m. The device has lower threshold current and larger T/sub 0/ than a device with GaInP cladding layers. This was expected from a larger bandgap difference between active and cladding layers.<>     

Linewidth enhancement factor in strained quantum well lasers

The linewidth enhancement factor α of strained quantum-well lasers is analyzed by the k-p perturbation method using the effective-mass approximation. It is found that the α factor in a strained In_0.80Ga_0.20As/InP quantum-well (QW) laser with 1.9% biaxial compression is less than 1.5. For a strained QW laser with p-type modulation doping (MD) of 5×10 ¹⁸ cm^-3, the α factor is as small as 0.8. It is also demonstrated that the spectral linewidth and wavelength chirping in the strained MD QW laser are significantly less than those in conventional bulk and QW lasers     

1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well (BH-GRIN-SC-MQW) lasers entirely grown by metalorganic chemical vapour deposition (MOCVD)

Reports the first successful demonstration of a 1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well laser (BH-GRIN-SC-MQW LD) entirely grown by three-step low pressure metal-organic chemical vapour deposition (LP-MOCVD). The threshold current and the differential quantum efficiency were 31 mA (threshold current density 3.4 kA/cm/sup 2/) and 28%/facet, respectively. A characteristic temperature of 65 K was obtained.<>     

Threshold current of 670-nm AlGaInP strained quantum well lasers

By means of gain-current calculations we have examined the factors which determine the threshold current of compressively strained Ga_x In_1-xP/AlGaInP quantum well lasers for the various well width/composition (x) combinations which give a transition wavelength of 670 nm. In addition to valence band modifications we find that the increasing depth and decreasing width of the well are important in decreasing the current as the strain increases. We reveal the important role of well width fluctuations in devices with high compressive strain     

Ultralow threshold strained InGaAs-GaAs quantum well lasers by impurity-induced disordering

Stripe-geometry strained InGaAs-GaAs quantum well lasers were fabricated by impurity induced disordering. Threshold currents as low as 2.2 mA at room temperature continuous operation (RT CW) were obtained for uncoated lasers having 1.2 mu m wide, 215 mu m long active stripes. The authors believe that this ultralow threshold is mainly due to the very small active stripe width and the excellent electrical confinement of the laser.<>     

Frequency modulation locking in 980 nm strained quantum well lasers

The fundamental and second-harmonic spectral characteristics of frequency modulation locking have been observed in strained-layer InGaAs quantum well Fabry-Perot ridge-waveguide lasers emitting at 980 nm.<>     

Anomalously high damping in strained InGaAs-GaAs single quantum well lasers

Measurements of the relative intensity noise spectra of strained, single-quantum-well, separate-confinement-heterostructure (SCH) InGaAs-GaAs lasers indicate that their frequency response is strongly damped. The ratio of the damping rate to the square of the resonance frequency is k=2.4 ns. This intrinsically limits the 3-dB modulation bandwidths of these lasers to about 4 GHz, negating the predicted increase in modulation bandwidth due to the large differential gain often associated with quantum-well devices. The damping behavior of these lasers is inconsistent with previous predictions of damping in bulk lasers due to spectral hole burning. A structure-dependent damping mechanism is proposed for quantum-well lasers.<>     

High temperature operation of lattice matched and strained InGaAs-InP quantum well lasers

The temperature dependence of lattice matched and strained InGaAs-InP quantum well lasers operating between 1.48 and 1.56 mu m is described. Devices grown under tensile and compressive strain, with an In concentration in the range of 0.43>     

Preliminary reliability studies of 1.55 mu m graded index separate confinement buried heterostructure (GRINSCH) multiple quantum well (MQW) lasers grown by metalorganic vapour phase epitaxy (MOVPE)

1.55 mu m graded index separate confinement heterostructure (GRINSCH) multi-quantum-well (MQW) lasers, grown entirely by metalorganic vapour phase epitaxy (MOVPE), have demonstrated low degradation rates in lifetests at 50 degrees C, 4 mW per facet. These lasers are complex structures, containing many interfaces, and the encouraging early lifetest results demonstrate the ability of MOVPE to grow these structures.<>     

Growth and optimization of extremely high-pulse-power graded-index separate confinement heterostructure quantum well AlGaAs/InGaAs diode lasers with broadened waveguides

Material quality is an essential prerequisite and a major challenge for the fabrication of high-power, 980-nm, strained-quantum-well (SQW) InGaAs lasers. We report our work aimed at metal-organic chemical vapor deposition (MOCVD) growth optimization and epitaxial quality analysis of various graded-index separate confinement heterostructure (GRINSCH) QW AlGaAs/InGaAs laser structures. Systematic investigation of doping level control and minimization of oxygen incorporation in AlGaAs were performed. Background oxygen levels of 10¹⁵ cm⁻³ were obtained with n-(Si) and p-(C) doping concentrations as high as 1 × 10¹⁸ cm⁻³ and 3 × 10¹⁸ cm⁻³, respectively, for Al_0.4Ga_0.6As layers. Double-crystal x-ray (DCXR), room-temperature photoluminescence (PL) mapping, Hall effect measurements, and secondary ion-mass spectroscopy (SIMS) techniques were used to evaluate material quality. A record, multimode, pulsed output power of 52.1 W has been obtained from 100-μm × 2-mm broad-stripe lasers made from these materials. The devices demonstrate low threshold current, low cavity losses, and kink-free light-current characteristics.     

A graded index single quantum well bistable laser

The authors report the first implementation of a buried heterostructure DOES (double heterostructure optoelectronic switch), which incorporates the principles of graded-index, single-quantum-well (GRIN SQW) lasers. Continuous operation and a small signal optical bandwidth of 1.5 GHz were obtained when biased into the on-state. This is consistent with the bond pad side employed. This GRIN SQW DOES laser, fabricated in two-terminal BH form, has been shown to have properties commensurate with the growth and processing parameters employed. Although limited to two-terminal operation, performance is comparable to existing devices with similar designs     

Carrier-induced differential refractive index in GaInAsP-GaInAsseparate confinement multiquantum well lasers

Measurements of subthreshold spectra on SCMQW (separate-confinement multiquantum-well) lasers with the number of wells varying from three to nine have led to the determination of the carrier-induced differential refractive index dμ/dN~-3.6×10^-20. This value is 1.8 greater than in the case of conventional bulk lasers. This study allows for a better understanding of quantum well laser parameters such as the spectral linewidth enhancement factor. It is also useful for the design of tunable lasers     

MBE growth and characteristics of periodic index separate confinement heterostructure InGaAs quantum-well lasers

We have used solid-source molecular beam epitaxy (MBE) to grow InGaAs quantum-well lasers emitting at 980nm in a novel configuration of periodic index separate confinement heterostructure (PINSCH). Periodic multilayers (GaAs/AlGaAs) are utilized as optical confinement layers to reduce the transverse beam divergence as well as to increase the maximum output power. The multilayers are grown by temperature modulation MBE without any shutter operation. The heterointerfaces in the multilayers are linearly graded such that the energy barrier heights are greatly decreased. This has led to a drastic reduction in the series resistance which is essential in the performance of high output power. The 5μm × 750μm device has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power of 620 mW, all measured at room temperature under CW operation. A record high fiber coupling efficiency of 51% has been achieved and more than 130 mW of power is coupled into a 5μm-core single mode fiber.     

Gain and index measurements in GaAlAs quantum well lasers

Measurements of the modal gain and group index in GaAlAs single-quantum-well (SQW) lasers are presented. The elimination of substrate emission has allowed accurate results to be obtained even in the near-bandgap and below-bandgap spectral regions. Substantial lifetime broadening is observed, and the gain smoothly goes to zero as the bandgap is approached. The group velocity index measurements indicate a dispersion of -3.44 μm^-1     

Dependence of linewidth enhancement factor on crystal orientationin strained quantum well lasers

The linewidth enhancement factor a in strained quantum well (QW) lasers is estimated theoretically for various crystallographic directions. It is found that the a factor in a strained In_0.7Ga_0.3As-InP QW laser on a (111) substrate is less than 1.4, much lower than for conventional strained QW lasers on (001) substrates     

Large estimated frequency response increase from deep potentialwell strained quantum well lasers

Effect of potential well depth on the maximum modulation bandwith has been analyzed for strained quantum well lasers emitting at 1.3 μm. The frequency response depends largely on the potential well depth. The maximum modulation bandwith of a deep-potential single-well SCH laser designed on a ternary substrate is estimated to be 25 GHz while that of the conventional InP based laser is 15 GHz. In a four-well case, the estimated bandwith of a laser designed on a ternary substrate is estimated to be 80 GHz     

Wavelength tuning in strained layer InGaAs-GaAs-AlGaAs quantum well lasers by selective-area MOCVD

Selective-area growth and regrowth using conventional atmospheric pressure metalorganic chemical vapor deposition is investigated for wavelength tuning in strained layer In_xGa_1-xAsGaAs-Al_y Ga_1-yAs quantum well lasers. Growth inhibition from a silicon dioxide mask is the mechanism used for the selective-area growth rate enhancement. By varying the width of the oxide stripe opening, differences in the growth rate yield different quantum well thicknesses, and hence different lasing wavelengths for devices on the same wafer. Both two-and three-step growth processes are utilized for selective-area epitaxy of strained layer In_xGa_1-xAs-GaAs quantum well active regions, with lasers successfully fabricated from the three-step growth. Scanning electron microscopy and transmission electron microscopy indicate that the absence of an oxide mask during Al_yGa_1-yAs growth is essential for successful device operation. A wide wavelength tuning range of over 630Å is achieved for lasers grown on the same substrate.