Very low threshold current ridge-waveguide AlGaAs/GaAs single-quantum-well lasers

Ridged-waveguide AlGaAs/GaAs single-quantum-well lasers were fabricated from a molecular-beam-grown GRIN-SCH wafer in which a superlattice buffer layer was introduced. Fabricated diodes exhibited excellent lasing characteristics including a very low threshold current of 5 mA with a T0 value as high as 160 K.     

Very low threshold GaInAsP/InP double-heterostructure lasers grown by LP MOCVD

Room-temperature GaInAsP/InP DH lasers emitting at 1.3 ?m and having very low threshold current densities have been grown by LP MOCVD. Thresholds were lower than the best values reported for comparable devices grown by LPE, the lowest threshold being 430 A/cm2 for a cavity length of 950 ?m (width 150 ?m) with an active-layer thickness of d = 2200 A.     

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.<>     

Very low threshold InGaAsP mesa laser

Very low threshold currents InGaAsP/InP terrace mesa (T-ME) lasers with an unpassivated surface have been fabricated on semi-insulating (SI) InP substrates. Fabrication of the lasers involves a single-step liquid phase epitaxial (LPE) growth and a simple etching process. Lasers operating in the fundamental transverse mode with threshold currents as low as 6.3 mA (for a cavity length of 250 μm) have been obtained. Comparison between the unpassivated lasers and those passivated using the mass transport technique is described.     

Analysis of threshold current density of CdZnSe/ZnSSe strained well lasers

The threshold current density (J/sub th/) of blue-green CdZnSe/ZnSSe strained quantum well lasers is analysed using the laser theory established for III-V semiconductor lasers. Very good agreement between theory and the reported experimental J/sub th/ values is obtained over a wide temperature range from 77 to 273 K. The optimal Cd composition of a CdZnSe single quantum well active layer for obtaining a low J/sub th/ value at room temperature is in the range 0.25-0.30.<>     

Very narrow-linewidth (70 kHz) 1.55 mu m strained MQW DFB lasers

A linewidth as narrow as 70 kHz together with a linewidth-power product of 0.2 MHz.mW have been achieved on 1450 mu m long compressively strained quantum well uniform DFB lasers. The results are achieved through a reduction of the phase-amplitude coupling factor, which is measured to be 1.7 times lower than in unstrained devices.<>     

Very low threshold current density 1.29 μm GaInNAs triple quantum well lasers grown by MBE

Very low threshold Ga_0.62In_0.38N_0.007As_0.993/GaN_0.011As_0.989/GaAs triple quantum well (QW) lasers emitting at 1.29 mum are demonstrated. The laser structure was grown by molecular beam epitaxy after extensive optimisations of growth and in situ annealing conditions. As- cleaved broad area lasers with a cavity length of 1 mm showed a record low threshold current density of 400 A/cm² (~130 A/cm² / QW), a high differential efficiency of 0.32 W/A/facet and a characteristic temperature of 94 K in the temperature range 10 to 110degC.     

AlInGaAs-AlGaAs strained single-quantum-well diode lasers

Diode lasers with a strained AlInGaAs active layer and AlGaAs confining and cladding layers are reported. Broad-stripe devices were fabricated in graded-index separate-confinement heterostructures grown by organometallic vapor-phase epitaxy on GaAs substrates and containing a single Al_yIn_xGa_1-x-yAs quantum well with 0.12⩽x⩽0.14 and five values of y between 0.05 and 0.17. With increasing Al content the emission wavelength decreases from 890 to 785 nm. The threshold current density J _th is less than 200 A-cm^-2, with one exception, and the differential quantum efficiency ranges from 78 to 81%. A preliminary reliability test was made on a saw-cut, uncoated broad-area device, with an Al_0.17In_0.12Ga_0.71As active layer, that was fabricated without using special precautions to minimize damage and was mounted junction side up. After 20 h of CW operations at a constant current of 1.125 times threshold, J _th has increased by only 3.5%     

Theoretical threshold lowering of compressively strained InGaAs/InGaAsP and GaInAsP/GaInAsP quantum-well lasers

The first theoretical evaluation is reported of the effect of biaxial compression on the quantum-well Ga/sub x/In/sub 1-x/As/Ga/sub 0.20/InAs/sub 0.45/P and Ga/sub 0.20/In/sub 0.80/As/sub y/P/sub 1-y//Ga/sub 0.20/In/sub 0.80/As/sub 0/ /sub .45/P/sub 0.55/ laser threshold current density. Reference is made to known experimental results, and a comparison carried out of the potentialities of the two types of laser.<>     

Design and fabrication of low-threshold 1.55-μm graded-indexseparate-confinement heterostructure strained InGaAsPsingle-quantum-well laser diodes

This paper presents a guideline for designing an optimum low-threshold 1.55-μm graded-index (GRIN) separate confinement-heterostructure (SCH) strained InGaAsP single quantum-well (SQW) laser diode (LD). The guideline was formulated based on the results of numerical and experimental analysis. After calculating the sheet carrier density at the lasing threshold, the guideline was obtained by considering the tradeoff between carrier and optical confinements in the well: the GRIN layer energy gap should be varied parabolically from InP to InGaAsP having a band gap wavelength of 1.1 μm to inject a large number of carriers into the well, and the thickness of one side of the GRIN layer should be more than 300 nm to keep a strong optical confinement. The GRIN SQW LD designed using the guideline has a J_th as low as 98 A/cm² at a cavity length of 5 mm, which proves the guideline is effective for designing low-threshold 1.55-μm GRIN SQW LDs     

Very low threshold Sagnac switch incorporating an erbium doped fibre amplifier

Fast, very low threshold optical pulse switching, in a nonlinear loop mirror incorporating an erbium doped fibre amplifier (EDFA) operating at 1.536 mu m with a gain of 46 dB is reported. For a 336 m Sagnac loop the input switching power is 200 mu W, which is 5*10/sup 3/ lower than the best previously reported.<>     

Band-structure engineering in strained semiconductor lasers

The influence of both compressive and tensile strain on semiconductor lasers and optical amplifiers is reevaluated in the light of recent experimental and theoretical work. Strain reduces the three-dimensional symmetry of the lattice and helps match the wave functions of the holes to the one-dimensional symmetry of the laser beam. It can also decrease the density of states at the valence band maximum and so reduce the carrier density required to reach threshold. These two effects appear to adequately explain the TE and TM gain in compressive and tensile structures, including polarization-independent amplifiers, the behavior of visible lasers and the improved frequency characteristics of InGaAs/GaAs lasers. In 1.5 μm InGaAsP/InP lasers phonon-assisted Auger recombination appears to remain the dominant current path and can explain why the temperature sensitivity parameter to remains <100 K at room temperature     

Low threshold 1.3 μm-GaInAsP/InP tensile strained single quantumwell lasers grown by low-pressure MOCVD

1.3 μm Ga_0.49In_0.51As_0.7P_0.3-1.15% tensile strained single quantum well (SQW) lasers are successfully fabricated. The lowest threshold current for a 200 μm-long, 20 μm-wide ridge waveguide laser with high reflectivity coating is as low as 6 mA, corresponding to a very low threshold current density of 150 A/cm²     

Very low threshold GRIN-SCH GaAs/GaAlAs laser structure grown by OM-VPE

In a recent publication we gave preliminary results on the lasing characteristics of a GRIN-SCH GaAs/GaAlAs laser grown by OM-VPE. The parameters of this single quantum well laser have now been further optimised, and for a quantum well thickness of 60 ?, with outer confinement layers composed of Ga0.4Al0.6As, significantly lower threshold current densities have been achieved. For a broad-area laser of cavity length 413 ?m (width 140 ?m) the average threshold current density is 232 A cm?2, and this decreases to 121 A cm?2 for a chip length of 1788 ?m. We believe that these are the lowest lasing threshold current densities that have yet been reported.     

High-temperature operation of InGaAs strained quantum-well lasers

Strained-layer quantum-well (SQW) laser structures have been investigated for avionics applications requiring high-temperature performance. The authors have successfully demonstrated InGaAs-GaAs SQW lasers capable of CW operation up to 200 degrees C with more than 5 mW single-mode optical power. These lasers have an emission wavelength of approximately=980 nm, threshold current density of 200 A/cm/sup 2/, differential quantum efficiency of 60%, high output power of approximately=1 W with 50 mu m stripe, and characteristic temperature of 130-140 K.<>     

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.<>     

Improved performance of long-wavelength strained bulk-likesemiconductor lasers

The authors show that the incorporation of either tensile or compressive strain can have significant advantages for long-wavelength bulk-like lasers, with greater advantage being achieved in tensile-strained structures. The differential gain is enhanced compared to unstrained structures and a larger peak gain can be achieved than in comparable structures under biaxial compression. The effect of the spin-orbit interaction on the polarized gain and character of the valence states is calculated as a function of built-in strain. The spin-split-off band is included in the calculations and it is shown that the strain-induced interaction with this band has a significant influence on laser characteristics. The effect of biaxial strain on the major intrinsic loss mechanism of Auger recombination in long-wavelength 1.55-μm lasers is investigated     

Channelled-substrate narrow-stripe GaAs/GaAlAs injection lasers with extremely low threshold currents

Channelled-substrate GaAs/GaAlAs injection lasers with very narrow current-confining stripe contacts are described. They have threshold currents less than half those previously reported for this type of device. The best devices had a room-temperature threshold current of only 12 mA pulsed and 14 mA c.w. The lasers also have very good high-temperature performance and c.w. operation has been obtained up to 160°C.     

High-temperature operation of InGaAs/InGaAsP compressive-strainedQW lasers with low threshold currents

We investigated the influence of the band gap wavelength of barrier layers and separate confinement heterostructure (SCH) layers λ_SCH on the high-temperature operation of InGaAs/InGaAsP compressive-strained quantum-well (QW) lasers. The optimum λ_SCH was 1.2 μm, at which carriers were sufficiently confined into quantum wells. The QW laser with λ_SCH = 1.2 μm exhibited low threshold currents of 2.3 mA at 20°C and 9.7 mA at 100°C and CW lasing up to 150°C     

Submilliamp threshold InGaAs-GaAs strained layer quantum-well laser

Strained-layer InGaAs-GaAs single-quantum-well buried-heterostructure lasers were fabricated by a hybrid beam epitaxy and liquid-phase epitaxy technique. Very low threshold currents, 2.4 mA for an uncoated laser (L=425 μm) and 0.75 mA for a coated laser (R~0.9, L=198 μm), were obtained. A 3-dB modulation bandwidth of 7.6 GHz was demonstrated at low bias current (14 mA). Procedures for material preparation and device fabrication are introduced