InGaAsP (λ=1.3 μm) strip buried heterostructure lasersgrown by MOCVD

The authors describe InGaAsP-InP index guides strip buried heterostructure lasers (SBH) operating at 1.3 μm with a 1.1-μm guiding layer grown by a two-step atmospheric pressure metalorganic chemical vapor deposition (MOCVD) growth procedure. These lasers are compared with buried heterostructure lasers having similar guiding layers under the active layer but terminated at the edge of the active layer. SBH lasers with 0.15-μm-thick active layer strips, 5-μm wide, and guide layers varying from 0 to 0.7 μm have threshold currents increasing from 34 to 59 mA, and nearly constant differential external quantum efficiencies of 0.2 mW/mA. The threshold current increases more rapidly with temperature with increasing guide layer thickness, with T₀ decreasing from 70°C for lasers without a guide layer to 54.3°C for lasers without a guide layer to 54.3°C for lasers with 0.7-μm-thick guide layers. Output powers of up to 30 mW/facet have been obtained from 254-μm-long lasers and were found to be insensitive to guide layer thickness     

Asymmetric cladding-ridge waveguide laser by selective-area MOCVD

Ridge waveguide lasers with a thin upper cladding layer are fabricated with a two-step selective-area MOCVD growth. The lower cladding, active region, and upper cladding are all grown in the initial MOCVD growth. A second growth over an oxide pattern is used to define the ridge with 0.15 μm of GaAs, which serves as both the contact and index increasing layer. Ridge lasers fabricated by this method (3×425 μm) have a cw threshold current of 12.6 mA, slope efficiency of 0.26 W/A, and operate in a fundamental transverse mode as well as stable fundamental lateral mode to 20 times threshold     

Reliability of 0.87 µm (Al,Ga)As double heterostructure lasers with Ga(As,Sb) active layers

Double-heterostructure injection lasers with additions of 1% Sb to the GaAs active layer have been found to have significantly improved reliability compared to lasers with binary GaAs active layers. Lasers with extrapolated room temperature median lifetimes of 10⁵hours have Ga(As,Sb) active layers that are lattice matched to the Al0.4Ga0.6As confinement layers. Furthermore, the addition of Sb to the LPE active layer growth melt apparently improves the initial nucleation and growth uniformity of the active layer.     

Pair-groove-substrate GaAs/AlGaAs multiquantum-well lasers with a self-aligned stripe geometry

GaAs/AlGaAs multiquantum-well (MQW) lasers with a self-aligned structure incorporating a waveguide and current confinement were fabricated on a substrate with a pair of etched grooves using two-step epitaxial growth. First, a current-blocking layer was grown selectively on the substrate by low-pressure organometallic vapour-phase epitaxy (OMVPE), and then the GaAs/AlGaAs MQW laser structure was constructed on the substrate with the OMVPE layer by molecular-beam epitaxy. The mesa-shaped part of the active layer above the current-confinement region provides a lateral refractive-index optical waveguide. The lasers show well controlled transverse-mode oscillations with low threshold currents.     

Suppression of interface degradation in InGaAsP inP buried heterostructure lasers

In InGaAsP/InP buried heterostructure (BH) lasers, the degradation of BH interface between first- and second-growth step layers can be suppressed by employing the melt back process just before the second-step layer growth. It is confirmed this burying process give more reliable BH lasers than the conventional burying process. From the viewpoint of BH interface degradation, lasers lasing at 1.5 μm, where the melt back process naturally occurs during BH formation, are found to be more reliable than those lasing at 1.3 μm.     

1.6 µm wavelength GaInAsP/InP lasers prepared by two-phase solution technique

Reduction of the threshold current of GaInAsP lasers with an antimeltback layer was studied in the wavelength range1.50-1.65 mun. The two-phase solution growth technique was applied using a relatively low temperature and a slow cooling rate of 0.17°C/min to reduce the active layer thickness. The antimeltback layer with a bandgap wavelength of 1.35 μm resulted in a flat active layer and eliminated the melt-back problem completely. From experiments and calculations we found that both the carrier and the optical confinement of this structure, having an antimeltback layer, were almost the same as those for the conventional InP cladding structure. A threshold eurrent density as low as 1.2 kA/cm²and an active layer thickness of 0.20μm were obtained at these wavelengths. The lattice-match condition of low-temperature growth was studied. In the low-temperature growth, the longer wavelength lasers were grown with the same amount of InAs.J_{th}/dwas independent of the growth condition (T_{S}, T_{G}) and had a value of 5-6 kA/cm². μm.     

Strained AlGaInAs/AlGaAs quantum wells and quantum-well lasersgrown by molecular beam epitaxy

Suitable growth conditions for strained AlGaInAs grown on GaAs substrates by molecular beam epitaxy (MBE) are presented, and strained layer multiple quantum well AlGaInAs lasers grown by MBE are demonstrated. Low-temperature photoluminescence was used to characterize quantum wells grown at different temperatures with different Al, Ga, and In compositions to establish growth parameters     

Transverse-junction-stripe GaAs-AlGaAs lasers for squeezed lightgeneration

We fabricated 850-nm GaAs transverse-junction-stripe (TJS) lasers by an improved metal-organic chemical vapor deposition (MOCVD) and double Zn diffusion process. The high V/III ratio used during the MOCVD growth significantly reduced the intermixing of GaAs active layer and AlGaAs cladding layers. The modified process realized good confinement for both carriers and photons and smaller saturable loss. We measured squeezing of -2.8 dB (-4.5 dB after correction for detection efficiency) at a pumping rate of I/I_th≈20 from these lasers, which is in close agreement with the theoretical limit. This squeezing remained unchanged under injection locking, indicating almost perfect conservation of the intensity noise correlation among the longitudinal modes. These TJS lasers had very small low-frequency 1/f noise     

Low-threshold operation of 1.3-μm GaAsSb quantum-well lasersdirectly grown on GaAs substrates

GaAsSb quantum-well (QW) edge-emitting lasers grown on GaAs substrates were demonstrated. The optical quality of the QW was improved by optimizing the growth conditions and introducing a multi-QW to increase the gain. As a result, 1.27-μm lasing of a GaAs_0.66 Sb_0.34-GaAs double-QW laser was obtained with a low-threshold current density of 440 A/cm², which is comparable to that in conventional InP-based long-wavelength lasers. 1.30 μm lasing with a threshold current density of 770 A/cm² was also obtained by increasing the antimony content to 0.36. GaAsSb QW was found to be a suitable material for use in the active layer of a 1.3-μm vertical-cavity surface-emitting lasers     

AlGaAs-GaAs-InGaAs strained layer laser structure with performance independent of AlGaAs layer quality

An AlGaAs-GaAs-InGaAs strained layer laser structure has been shown to have a low threshold current density which is independent of AlGaAs layer quality. This threshold invariance is attributed to the use of a large GaAs region outside the InGaAs well to reduce the effects of traps in the AlGaAs on the active region of the laser and was demonstrated by characterising identical structures grown by molecular beam epitaxy (MBE) under different AlGaAs growth conditions. These results should have strong implications for the reliability and manufacturability of such lasers and for the integration with electronic devices where low temperature growth is required.<>     

High frequency buried heterostructure 1.5 μm GaInAsP/InP lasers,grown entirely by metalorganic vapour phase epitaxy in two epitaxialgrowth steps

A new high frequency buried heterostructure laser is described and fabricated using two epitaxial growth steps, grown entirely by atmospheric pressure metalorganic vapour phase epitaxy. The lasers are made with non-re-entrant mesas with the active layer narrowed to 1-2 μm by a selective etch to ensure operation in the lowest order transverse mode. The regrowth with Fe doped semi-insulating InP fills in the etched slots adjacent to the active layer and planarises the structure. The non-re-entrant mesa eliminates the anomalous rapid growth in MOVPE at the edges of the re-entrant mesas. The lasers have thresholds of 20 mA and quantum efficiencies of 46% with good linearity up to 10 mW. The laser shows a small signal microwave bandwidth of 5.8 GHz at 5 mW     

Effects of electronic current overflow and inhomogeneous carrier distribution on InGaN quantum-well laser performance

Laser performance of several InGaN quantum-well (QW) lasers with an emission wavelength of 392-461 nm are numerically studied with a LASTIP simulation program. Specifically, the effects of electronic current overflow and inhomogeneous carrier distribution on the laser performance of InGaN QW lasers operating at different wavelengths are investigated. Simulation results indicate that the use of an AlGaN blocking layer can help reduce the electronic current overflow and, in addition to the dissociation of the InGaN well layer at a high growth temperature during crystal growth, the inhomogeneous carrier distribution in the QWs also plays an important role in the laser performance. From the simulation results, we conclude that the lowest threshold current density is obtained when the number of InGaN well layers is two if the emission wavelength is shorter than 427 nm and one if the emission wavelength is longer than 427 nm, which are in good agreement with the results observed by Nakamura et al. in their experiments.     

Three- and four-layer LPE InGaAs(P) mushroom stripe lasers for λ = 1.30, 1.54, and 1.66 µm

Mushroom stripe (MS) InGaAsP/InP and InGaAs/InP lasers have been realized emitting atlambda = 1.3, 1.54,and 1.66 μm, respectively. The main advantage of these MS lasers is their technological simplicity, because only one epitaxial growth step consisting of three or four layers, respectively, is required. No contact layer and no filling layers are needed. In our phosphorus silicate glass (PSG) passivated MS lasers, current spreading is completely inhibited. The devices have very low CW threshold currents and high values of output power, external differential efficiency, and To. All these properties are equivalent to those of the much more complicated buried heterostructure lasers. CW operation in up-side-up mounted MS lasers on p-type substrates is easily achieved, because their series resistance is very low. The devices oscillate in the fundamental lateral mode for easily achievable width and thickness combinations, and tend to longitudinal monomode behavior at moderate output powers. The modulation capability is more than 1 Gbit/s RZ due to the low capacitance of the mushrooms. The commonly used antimeltback layer for lasers withlambda > 1.5 mum on     

Tem study of dark line defect growth from dislocation clusters in (GaAl)As-GaAs double heterostructure lasers

Dark spot defects in (GaAl)As-GaAs double heterostructure lasers are studied by transmission electron microscopy and found to be a cluster of dislocations generated in the first (GaAl)As epitaxial layer during epitaxial growth. Burgers vectors and spatial configuration of dislocation dipoles developing from these dislocations are determined. It is found that Burgers vectors of dislocations in the dislocation cluster obey the Burgers vector sum rule.     

Semiconductor lasers fabricated by selective area epitaxy

For the first time, semiconductor lasers grown entirely by selective area epitaxy are reported. The lasers were formed by in situ processing techniques and metal organic molecular beam epitaxy (MOMBE). A 50 AA thick layer of Si deposited on the InP substrate was used as a mask for both the selective growth and etching. Laser stripes, 6 mu m wide, were delineated by a focused Ga ion beam and transferred into the substrate by Cl/sub 2/ etching. These steps were performed in the vacuum chambers attached to the MBE machine. Separate confinement heterostructure GaInAsP-InP lasers were grown selectively in the stripes. The resulting devices emit at 1.3 mu m and show threshold currents of 40 mA.<>     

Fabrication and lasing properties of mesa substrate buried heterostructure GaInAsP/InP lasers at 1.3 µm wavelength

Fabrication and lasing properties of novel GaInAsP/InP injection lasers at 1.3 μm, with buried heterostructure grown on mesa substrate and fabricated by single-step crystal growth are reported. In this mesa substrate buried heterostructure (MSB) laser, the GaInAsP active layer was grown separately on the top of a mesa structure formed along the surface of a     

Temperature characteristics of double-carrier-confinement (DCC) heterojunction InGaAsP(λ = 1.3 µm)/InP lasers

This paper reports on a detailed study of the oscillation characteristics of double-carrier-confinement (DCC) heterojunction InGaAsP(lambda = 1.3 mum)/InP lasers, with special emphasis on their temperature characteristics. In addition to conventional double-heterojunction lasers, these lasers have a p-InGaAsP second active layer sandwiched between the p-InP clad layers. The spectral characteristics below threshold were examined in order to verify electron leakage beyond the hetero-barrier of the p-InP thin clad layer, and to study the contribution of the second active layer to optical gain and laser action. Threshold temperature characteristics were also investigated through an analysis of the heterojunction energy band structure. The results indicate that emission from the second active layer is caused by electron leakage. In order to obtain high temperature stability for these lasers, it is essential that both the first and second active layers contribute to the optical gain spectrum and laser action.     

Reliability in InGaAsP/InP buried heterostructure 1.3 µm lasers

A study was conducted of aging-induced Sn whisker growth at the surface of Au-Sn bonding solder layers around a laser chip, as well as metallurgical reactions, especially in p-side down lasers, at the interface of the solder and laser crystal just below the active layer. These phenomena cause electrical shorts in InGaAsP/InP laser diodes, which occur suddenly in devices operated for long periods without any previous symptoms having appeared in their aging characteristics. To completely eliminate such failures, a novel assembling method in which chips were mounted p-side up on semiinsulating SiC submounts using Pb-Sn solder, was applied to InGaAsP/InP buried heterostructure (BH) lasers emitting at 1.3 μm. BH lasers assembled by this method do not suffer any shorting failure even after 8000 h operation under 60°C and 5 mW/facet output conditions. The small degradation rates obtained, for example, 3 percent/kh (median) at 60°C, certify the reliability of these improved lasers. As long as the stripe width of the active layer was optimized to be in the range of1.5-2.5 mum necessary for obtaining kink-free light output versus current properties, no detrimental changes in laser characteristics, including transverse and longitudinal modes and dynamic output response, were observed in aged lasers. In this paper, the long-term degradation modes observed are presented, and possible causes are discussed.     

Very narrow linewidth asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers

Asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector (RW-DBR) lasers are demonstrated with a spectral linewidth as low as 39 kHz for an output power of 24 mW. The fabrication requires only a single standard epitaxial growth of a laser structure while the use of a thin top cladding layer allows for a shallow reactive ion etch of the distributed Bragg reflector. These RW-DBR lasers have a threshold current of 12.4 mA, a slope of 0.3 W/A, and over 40 dB side-mode suppression at a wavelength of 1010 nm.     

Recombination enhanced annealing effect in AlGaAs/GaAs remote junction heterostructure lasers

New structure lasers, the remote junction heterostructure (RJH) lasers, are made to obtain information about slow degradation of AlGaAs/GaAs DH lasers. The RJH laser is characterized by the presence of a thin clad layer between the active layer and the p-n junction. During the LD and LED mode aging process, the RJH lasers showed a marked reduction of threshold current. This reduction was accompanied by increased spontaneous lifetime and pileup of defects at the p-n junction. From these observations, a model was proposed in which point defect generation in the active layer and defect motion toward the p-n junction during the aging are assumed. The rate equation was derived for concentration of the point defect, and the solution of this equation was compared with the experimental results with reasonable agreement. The parameters relating to the slow degradation were determined, and the ultimate life of conventional DH lasers was discussed using these parameters.