High-performance strain-compensated InGaAs-GaAsP-GaAs(λ=1.17 μm) quantum well diode lasers

This letter reports studies on highly strained and strain-compensated InGaAs quantum-well (QW) active diode lasers on GaAs substrates, fabricated by low-temperature (550°C) metal-organic chemical vapor deposition (MOCVD) growth. Strain compensation of the (compressively strained) InGaAs QW is investigated by using either InGaP (tensile-strained) cladding layer or GaAsP (tensile-strained) barrier layers. High-performance λ=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm² for 1500-μm-cavity devices and transparency current densities of 50 A/cm². The use of GaAsP-barrier layers are also shown to significantly improve the internal quantum efficiency of the highly strained InGaAs-active laser structure. As a result, external differential quantum efficiencies of 56% are achieved for 500-μm-cavity length diode lasers     

1.58-μm lattice-matched and strained digital alloy AlGaInAs-InPmultiple-quantum-well lasers

A versatile, digital-alloy molecular beam epitaxy (MBE) technique is employed to grow lattice-matched and strained AlGaInAs multiple-quantum well (MQW) 1.58-μm laser diodes on InP. A threshold current density as low as 510 A/cm² has been demonstrated for broad area lasers with 1% strained AlGaInAs MQWs, which is the best MBE result in this material system. A single facet pulsed power as high as 0.56 W is obtained. It is also found that the efficiency and internal loss of digital alloy AlGaInAs QW devices are comparable to lasers grown by conventional MBE     

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     

Threshold current analysis of compressive strain (0-1.8%) inlow-threshold, long-wavelength quantum well lasers

A comprehensive study of the effect of compressive strain on the threshold current performance of long-wavelength (1.5 μm) quantum-well (QW) lasers is presented. Model predictions of threshold currents in such devices identify QW thickness as a parameter that must be considered in optimizing laser performance when Auger currents are present. Experimental comparisons between strained and unstrained devices reveal strain-induced reductions in internal transparency current density per QW from 66 to 40 A/cm², an increase in peak differential modal gain from 0.12 to 0.23 cm/A, and evidence for the elimination of intervalence band absorption as compressive strain increases from 0 to 1.8%. However, most of these improvements arise in the first ~1% of compressive strain. To fabricate low-threshold 1.5-μm buried heterostructure (BH) devices in InP using the strained QW active regions an optimized design which shows that threshold current is at its lowest when the stripe width is approximately 0.6-0.7 μm is derived. Results for uncoated BH lasers are reported     

MBE生长InGaAs／GaAs应变层单量子阱激光器结构材料的研究

采用ＶａｒｉａｎＧｅｎⅡＭＢＥ生长系统研究了ＩｎＧａＡｓ／ＧａＡｓ应变层单量子阶（ＳＳＱＷ）激光器结构材料。通过ＭＢＥ生长实验，探索了Ｉｎ＿ｘＧａ＿（１－ｘ）ｔＡｓ／ＧａＡｓＳＳＱＷ激光器发射波长（λ）与Ｉｎ组分（ｘ）和阱宽（Ｌ＿ｚ）的关系，并与理论计算作了比较，两者符合得很好。还研究了材料生长参数对器件性能的影响，主要包括：Ⅴ／Ⅲ束流比，量子阱结构的生长温度Ｔ＿ｇ（ＱＷ），生长速率和掺杂浓度对激光器波长、阈值电流密度、微分量子效率和器件串联电阻的影响。以此为基础，通过优化器件结构和ＭＢＥ生长条件，获得了性能优异的Ｉｎ＿（０．２）Ｇａ＿（０．８）Ａｓ／ＧａＡｓ应变层单量子阱激光器：其次长为９６３ｎｍ，阈值电流密度为１３５Ａ／ｃｍ￣２，微分量子效率为３５．１％。     

Room-temperature 2.81-/spl mu/m continuous-wave operation of GaInAsSb-AlGaAsSb laser

GaInAsSb-AlGaAsSb multiple quantum-well (QW) lasers with an emission wavelength of 2.81 /spl mu/m are reported. The ridge waveguide lasers with highly strained QWs show continuous-wave laser emission up to 25/spl deg/C; in pulsed mode, the lasers operate up to 60/spl deg/C. For pulsed operation, a threshold current density of 360 A/cm/sup 2/ is found for devices with 30-/spl mu/m stripe width and 2-mm cavity length at room temperature. A low threshold current density at infinite length of 248 A/cm/sup 2/ is derived.     

The influence of quantum-well composition on the performance ofquantum dot lasers using InAs-InGaAs dots-in-a-well (DWELL) structures

The optical performance of quantum dot lasers with different dots-in-a-well (DWELL) structures is studied as a function of the well number and the indium composition in the InGaAs quantum well (QW) surrounding the dots. While keeping the InAs quantum dot density nearly constant, the internal quantum efficiency η_i, modal gain, and characteristic temperature of 1-DWELL and 3-DWELL lasers with QW indium compositions from 10 to 20% are analyzed. Comparisons between the DWELL lasers and a conventional In_0.15Ga_0.85As strained QW laser are also made. A threshold current density as low as 16 A/cm² is achieved in a 1-DWELL laser, whereas the QW device has a threshold 7.5 times larger. It is found that η_i and the modal gain of the DWELL structure are significantly influenced by the quantum-well depth and the number of DWELL layers. The characteristic temperature T₀ and the maximum modal gain of the ground-state of the DWELL structure are found to improve with increasing indium in the QW It is inferred from the results that the QW around the dots is necessary to improve the DWELL laser's η_i for the dot densities studied     

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     

Analysis of the performance of 1.55-μm InGaAs-InP tensilestrained quantum-well lasers

We fabricated 1.55-μm tensile strained InGaAs quantum-well (QW) lasers into broad-area and ridge waveguide lasers, and their performance was analyzed and compared with compressive strained and lattice-matched QW lasers. It is seen that the limitation on the tensile strain to a value less than 0.7%, which is required to prevent the emission wavelength being shorter than 1.55 μm, imposes restrictions on the performance enhancement in several aspects. Broad-area InGaAs QW lasers with a tensile strain of 0.7% show a larger gain coefficient and smaller transparency current density per well than those with InGaAsP QW lasers with a compressive strain of 1.0%. However, the internal quantum efficiency is much smaller than that for compressive ones and the internal optical loss increases rapidly as the number of QW's increases. These are thought to be caused by a smaller conduction band offset and the onset of dislocation generation at the well-barrier interfaces with the number of QW's, respectively. Ridge waveguide lasers with two QW's with tensile strain of 0.7%, which is designed not to exceed the critical thickness for dislocation generation, show smaller modal gain coefficients and inferior temperature characteristics as compared to those with six 0.7% compressive strained QW's and those with three lattice matched InGaAs QW's. However, the modulation bandwidth is measured to be larger than that for one that is compressively strained. It is believed to originate from the small effective capture time of the carriers due to thicker wells     

1.3 /spl mu/m GaAs/GaAsSb quantum well laser grown by solid source molecular beam epitaxy

A highly strained GaAs/GaAs/sub 0.64/Sb/sub 0.36/ single quantum well laser has been grown on GaAs (100) substrate by using solid source molecular beam epitaxy. The uncoated broad-area laser demonstrates 1.292 /spl mu/m pulsed operation with a low threshold current density of 300 A/cm/sup 2/. The spontaneous emission of the laser was also studied. The result reveals that the Auger recombination component dominates the threshold current at high temperature.     

Threshold current density in strained layerInxGa1-xAs-GaAs quantum-well heterostructurelasers

The authors consider the transparency carrier density in ideal and practical strained layer In_xGa_1-xAs-GaAs quantum-well heterostructure lasers. The transparency carrier density in practical structures is then related to transparency current density using realistic values for spontaneous recombination rates. These parameters are incorporated with representative structural parameters into a nonlinear model for gain in a quantum-well laser, in order to provide a complete model for the laser threshold current density in strained layer In_xGa_1-xAs-GaAs quantum-well heterostructure lasers. These results are then compared and contrasted with experimental laser results from several laboratories     

Low threshold current 1.5-μm buried heterostructure lasers usingstrained quaternary quantum wells

Buried heterostructure lasers operating at a wavelength of 1.5 μm with four compressively strained quaternary quantum wells (strain ~1.8%, thickness ~90 Å) and current blocking layers were made using atmospheric pressure metalorganic chemical vapor deposition. Pulsed room-temperature threshold currents for uncoated devices as low as 4.1 mA and as low as 0.8 mA for devices with high reflectivity mirror coatings are reported. The dependence of threshold current on active region width is consistent with broad-area laser measurements     

Gain and linewidth enhancement factor in InAs quantum-dot laserdiodes

Amplified spontaneous emission measurements are investigated below threshold in InAs quantum-dot lasers emitting at 1.22 μm. The dot layer of the laser was grown in a strained quantum well (QW) on a GaAs substrate. Ground state gain is determined from cavity mode Fabry-Perot modulation. As the injection current increases, the gain rises super-linearly while changes in the index of refraction decrease. Below the onset of gain saturation, the linewidth enhancement factor is as small as 0.1, which is significantly lower than that reported for QW lasers     

Low-threshold-current-density 1.5 μm lasers using compressivelystrained InGaAsP quantum wells

A low-threshold current density (J_th) of 140 A/cm² for broad-area 1.5-μm semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm^-1 and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm². Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J_th of 324 A/cm² at L=1.5 mm     

Analysis of differential gain in InGaAs-InGaAsP compressive andtensile strained quantum-well lasers and its application for estimationof high-speed modulation limit

A simplified model that furnishes an intuitive insight for the change in quantum-well (QW) laser gain due to QW strain and quantum confinement is presented. Differential gain for InGaAs-InGaAsP compressive and tensile strained multi-quantum-well (MQW) lasers is studied using the model. The comparison between the calculated and experimental results for lattice-matched and compressive strained MQW lasers shows that this model also gives quantitatively reasonable results. It is found that the variance-band barrier height strongly affects the differential gain, especially for compressively strained MQW lasers. The tensile strained MQW lasers are found to have quite high differential gain, due to the large dipole matrix element for the electron-light-hole transition, in spite of the large valence-band state density. Furthermore, a great improvement in the differential gain is expected by modulation p doping in the tensile strained MQW lasers. The ultimate modulation bandwidth for such lasers is studied using the above results     

Very-low-threshold current density 1.29 μm GaInNAs triple quantum well lasers grown by molecular beam epitaxy

Very-low-threshold Ga_0.62In_0.38N_0.007As_0.993/GaN_0.011 As_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 under pulsed operation showed a record low-threshold current density of 400 A/cm² (~130A/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 quantum-well ridge waveguide lasers grownby metalorganic chemical vapor deposition

AlInGaAs/AlGaAs strained quantum-well ridge waveguide diode lasers with an emission wavelength of 890 nm are presented. These devices exhibit both single spatial and longitudinal mode operation up to 30 mW of optical output power. A CW threshold current of 13 mA was obtained for a 5-μm-wide ridge waveguide having a cavity length of 500 μm. The differential quantum efficiency was 52%. The lateral and perpendicular far-field radiation patterns (FWHM) from the laser were 6° and 51°, respectively. Reliability testing on uncoated gain-guided lasers made from the same wafer showed no sudden death failures and degradation rates as low as 4.6%/kh     

A new InGaAs/InGaAsP delta -strained multiple-quantum-well laser grown by chemical-beam epitaxy

The authors propose and demonstrate a delta -strained multiple-quantum-well laser in which the quantum well is composed of a thin strained layer ( approximately AA In/sub x/Ga/sub 1-x/As) sandwiched by lattice-matched (In/sub 0.53/Ga/sub 0.47/As) layers. A threshold current density of 510 A/cm/sup 2 /was obtained from broad-area lasers with four delta -strained quantum wells and a cavity length of 3 mm, with an emission wavelength near 1.55 mu m. The use of a delta -strained quantum well provides an additional degree of freedom in optimizing the amount of strain and thickness of the active layer in improving the device performance.<>     

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%     

Low-threshold 1.5 μm compressive-strained multiple- andsingle-quantum-well lasers

Design considerations for low-threshold 1.5-μm lasers using compressive-strained quantum wells are discussed. Parameters include transparency current density, maximum modal gain, bandgap wavelength, and carrier confinement. The optical confinement for a thin quantum well in the separate-confinement heterostructure (SCH) and the step graded-index separate-confinement heterostructure (GRINSCH) are analyzed and compared. 1.5-μm compressive-strained multiple- and single-quantum-well lasers have been fabricated and characterized. As a result of the compressive strain, the threshold current density is loss limited instead of transparency limited. By the use of the step graded-index separate-confinement heterostructure to reduce the waveguide loss, a low threshold current density of 319 A/cm² was measured on compressive-strained single-quantum-well broad-area lasers with a 27 μ oxide stripe width