Uniform linear arrays of strained-layer InGaAs-AlGaAs quantum-wellridge-waveguide diode lasers fabricated by ECR-IBAE

Uniform linear arrays of strained-layer multiple-quantum-well InGaAs-AlGaAs ridge-waveguide diode lasers have been fabricated that operate near 980 nm and have low threshold currents I_th and high differential quantum efficiencies η_d. Uniformity was achieved by a combination of uniform ion-beam-assisted etching with an electron cyclotron resonance ion source and uniform organometallic vapor-phase epitaxial (OMVPE) growth. We investigated the effects of device geometry, namely, ridge width, cavity length, and remaining cladding thickness outside the ridge t, on I_th and η_d. For uncoated lasers with 500-μm-long cavities, 2- to 3-μm-wide ridges, and t=165±75 nm fabricated in double-quantum-well OMVPE material, I_th was typically in the range 6-7 mA and η_d was >40% per facet. A 24-element array of 2-μm-wide, 200-μm-long ridge-waveguide lasers with a high reflection coating on the back facet exhibited excellent uniformity, with threshold currents and single-ended differential quantum efficiencies that averaged 3.4 mA and 72%, respectively. Similar arrays with high-reflectivity coatings on both facets exhibited threshold currents as low as 2 mA     

1.3-μm AlGaInAs-InP buried-heterostructure lasers with modeprofile converter

AlGaInAs buried-heterostructure (BH) lasers with a mode profile converter (MPC) have been successfully fabricated for the first time. The thickness of the multiple-quantum-well (MQW) waveguide was vertically tapered by selective area growth (SAG). The threshold current I_th was 14.6 mA with a 600-μm-long cavity and a high-reflective-coated rear facet. The full-width at half-maximum of the far-field pattern in the perpendicular and horizontal directions were 9.2° and 12.6°, respectively. The optical coupling loss between lasers with MPC and a single-mode fiber was 3.0 dB when the distance between the laser and fiber was 20 μm     

High temperature, high power InGaAs/GaAs quantum-well lasers withlattice-matched InGaP cladding layers

The authors report the high-temperature and high-power operation of strained-layer InGaAs/GaAs quantum well lasers with lattice-matched InGaP cladding layers grown by gas-source molecular beam epitaxy. Self-aligned ridge waveguide lasers of 3-μm width were fabricated. These lasers have low threshold currents (7 mA for 250-μm-long cavity and 12 mA for 500-μm-long cavity), high external quantum efficiencies (0.9 mW/mA), and high peak powers (160 mW for 3-μm-wide lasers and 285 mW for 5-μm-wide laser) at room temperature under continuous wave (CW) conditions. The CW operating temperature of 185°C is the highest ever reported for InGaAs/GaAs/InGaP quantum well lasers, and is comparable to the best result (200°C) reported for InGaAs/GaAs/AlGaAs lasers     

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     

Design criteria of 1.3-μm multiple-quantum-well lasers forhigh-temperature operation

We present design criteria for high-temperature operation in 1.3-μm multiple-quantum-well (MQW) lasers from the viewpoint of the light output power penalty, i.e., the change in the light output power at a fixed drive current with increasing temperature. It is shown that not only the characteristic temperature (T₀) but also internal loss dependence on temperature (γ) and threshold current (I_th) are significant parameters for reducing the power penalty. We compare the high-temperature performance of InGaAsP-based and AlGaInAs-based MQW lasers and demonstrate that AlGaInAs-based lasers have more potential in terms of the power penalty. Furthermore, we also demonstrate that the power penalty can be reduced by introducing a buried-heterostructure (BH) structure into AlGaInAs-based lasers. From these results, we conclude that the AlGaInAs-based BH lasers are promising for high-temperature performance     

GaAs:GaAlAs ridge waveguide lasers and their monolithic integrationusing the ion beam etching process

The fabrication and performance characteristics of GaAs/GaAlAs ridge waveguide lasers are discussed. Threshold currents as low as 8 mA and differential quantum efficiencies as high as 90% were obtained for 250-μm-long graded-index separate-confinement heterostructure with single quantum well (GRINSCH SQW) lasers. High-speed short-cavity ridge waveguide lasers for which both the ridge stripe and one-mirror facet were formed by Ar-ion beam etching were achieved. The dependence of threshold current and lasing spectra on the cavity length were theoretically and experimentally investigated. This process was successfully used to integrate a laser diode monolithically with a photodiode or a field-effect transistor     

Study on the dominant mechanisms for the temperature sensitivity ofthreshold current in 1.3-μm InP-based strained-layer quantum-welllasers

We study the basic physical mechanisms determining the temperature dependence of the threshold current (I_th) of InP-based strained-layer (SL) quantum-well (QW) lasers emitting at a wavelength of 1.3 μm. We show that I_th exhibits a different temperature dependence above and below a critical temperature T_c. It is indicated that T_c is the maximum temperature below which the threshold gain exhibits a linear relationship with temperature. We demonstrate that below T_c the Auger recombination current dominates the temperature dependence of I_th. On the other hand, above T_c a significant increase in both the internal loss and radiative recombination current in the separate-confinement-heterostructure region, which is mainly due to electrostatic band-profile deformation, is found to play a major role in determining the temperature sensitivity of I_th. On the basis of the comparison between the theoretical analysis and the experimental results, we conclude that the temperature dependence of the threshold current in 1.3-μm InP-based SL-QW lasers is dominated by different mechanisms above and below T_c     

The effect of temperature dependent processes on the performance of1.5-μm compressively strained InGaAs(P) MQW semiconductor diodelasers

We describe measurements of the threshold current I_th and spontaneous emission characteristics of InGaAs (P)-based 1.5-μm compressively strained multiple-quantum-well semiconductor lasers from 90 K to above room temperature. We show that below a break-point temperature, T_B≈130 K, I_th and its temperature dependence are governed by the radiative current. Above this temperature, a thermally activated Auger recombination process becomes the dominant recombination mechanism responsible for both I_th and its temperature sensitivity. At room temperature nonradiative Auger recombination is found to account for approximately 80% of the threshold current in these devices     

1.5-μm strained-layer MQW-DFB lasers with highrelaxation-oscillation frequency and low-chirp characteristics

1.5-μm wavelength strained-layer multiple-quantum-well (SL-MQW) distributed-feedback (DFB) lasers for optical video distribution systems, including optical-fiber amplifiers, are studied with respect to the relaxation-oscillation frequency and wavelength chirp characteristics. Several types of lasers are examined as parameters of amount of strain, optical confinement, and detuning. It is confirmed that the introduction of negative detuning has an obvious effect on the increase in relaxation-oscillation frequency f_r and the reduction in chirp ΔF. The SL-MQW DFB lasers with low optical confinement and negative detuning show extremely low FM response ΔF/ΔI of less than 60 MHz/mA as well as high f_r over 10 GHz for the first time. Additionally, low-chirp value ΔF of 180 MHz with modulation depth of 10% is realized at relatively low bias current (I_h=I_th+30 mA)     

Monolithic integration in InGaAs-InGaAsP multiquantum-wellstructure using laser processing

We report the use of a laser irradiation process, which combines irradiation by continuous wave and Q-switched pulsed Nd:YAG lasers, to promote quantum-well intermixing. Differential shifts up to 70 meV have been obtained in GaInAsP structures. Extended cavity-ridge lasers with 800-μm-long active sections and 1000-μm-long passive sections, were fabricated. The slope efficiency of the extended cavity lasers is very close to that of 800-μm-long all-active lasers, and the threshold current is 10 mA higher than for an 800-μm-long all-active device. The loss in the intermixed single-mode waveguide is 2.1 cm^-1     

Molecular beam epitaxy-grown PbSnTe-PbEuSeTe buried heterostructurediode lasers

Buried heterostructure (BH) PbSnTe-PbEuSeTe lasers with a PbSnTe active layer were fabricated for the first time using a two-stage molecular beam epitaxy (MBE) growth procedure. Lasers with 4-μm-wide and 0.65-μm-thick buried Pb_0.961Sn_Sn0.039Te active layer and Pb_0.985Eu_0.015Se_0.02Te _0.98 cladding layers were grown. Continuous wave (CW) operating temperature of 175 K was measured with CW threshold currents of 1.6 mA (20 K), 13.6 mA (80 K), and 195 mA (160 K). Single-mode operation with 3.0-cm^-1-mode tuning was measured at 1639.8 cm ^-1 emission     

Antiguided array diode lasers fabricated with modulated cap thinp-clad structure

Antiguided array lasers were fabricated in thin p-clad, InGaAs-GaAs single quantum-well material. The required lateral refractive index variation was achieved by precisely modulating the thickness of the GaAs cap layer using a novel pulsed anodization/etching technique. Edge-emitting arrays having 20 lasers on 7-μm centers with 5-μm-wide gain regions were characterized. At 1.2 times the pulsed current threshold (I_th), the central lobe of the lateral far field of the arrays contained about 75% of the beam power and was about twice the diffraction limit (FWHM=0.8°). At 10×I_th, the central lobe contained about 60% of the beam power and was about 1.6° wide     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

Single-Facet Folded-Cavity Diode Laser With Ultrasmall Bend Radius High-Index-Contrast Oxidized AlGaAs Ridge Waveguide

AlGaAs heterostructure high-index-contrast (HIC) ridge waveguide (RWG) diode lasers incorporating a folded-cavity single-facet resonator with a folding bend radius as small as r=10 mum are demonstrated. Fabricated by a self-aligned deep dry etch (through the active region) plus nonselective O₂-enhanced wet thermal oxidization process, the low-index, insulating, and interface-passivating wet thermal oxide grown directly on the etch-exposed AlGaAs waveguide sidewalls yields a high lateral refractive index contrast of Deltan~1.7 and provides strong optical mode confinement. The HIC RWG device geometry also completely eliminates lateral current spreading, which results in an excellent overlap between the optical field and the gain region of the single InAlGaAs quantum-well graded-index separate confinement heterostructure. A threshold current of I_th=65mA is obtained for the r=10 mum device (a half-racetrack ring resonator), giving a threshold current density of Jth=1503 A/cm², 3.34 times higher than that of same-length straight lasers. At a bend radius of r=150 mum, I_th=16.6 mA, and J_th is comparable to straight cavity values, indicating that at this curvature there is negligible bending and scattering loss for the lowest-order waveguide mode     

1.3-μm InAsP modulation-doped MQW lasers

The effect of both n-type and p-type modulation doping on multiple-quantum-well (MQW) laser performances was studied using gas-source molecular beam epitaxy (MBE) with the object of the further improvement of long-wavelength strained MQW lasers. The obtained threshold current density was as low as 250 A/cm² for 1200-μm-long devices in n-type modulation-doped MQW (MD-MQW) lasers. A very low CW threshold current of 0.9 mA was obtained in 1.3-μm InAsP n-type MD-MQW lasers at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest value for lasers grown by all kinds of MBE in the long-wavelength region. Both a reduction of the threshold current and the carrier lifetime in n-type MD MQW lasers caused the reduction of the turn-on delay time by about 30%. The 1.3-μm InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay time are very attractive for laser array applications in high-density parallel optical interconnection systems. On the other hand, the differential gain was confirmed to increase by a factor of 1.34 for p-type MD MQW lasers (N_A=5×10¹⁸ cm ^-3) as compared with undoped MQW lasers, and the turn-on delay time was reduced by about 20% as compared with undoped MQW lasers. These results indicate that p-type modulation doping is suitable for high-speed lasers     

Low threshold current high-temperature operation of InGaAs/AlGaAsstrained-quantum-well lasers

The authors report improved high-temperature characteristics for In_0.2Ga_0.8As strained-quantum-well ridge waveguide lasers with an optimized cavity design. They have fabricated In_0.2 Ga_0.8As lasers that operate CW at up to 220°C with over 9-mW output power. At 200°C the threshold current is as low as 15.9 mA for a 400-μm-long laser with 35/98% reflectivity facets. Optimization of the laser cavity also improves the high-temperature operation of quantum-well lasers in other material systems; GaAs quantum well lasers that operate at up to 220°C CW have been fabricated     

1.3-μm CW lasing characteristics of self-assembled InGaAs-GaAsquantum dots

This paper presents the lasing properties and their temperature dependence for 1.3-μm semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-μm emission dots were successfully grown by the combination of low-rate growth and InGaAs-layer overgrowth using molecular beam epitaxy. 1.3-μm ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25°C with a realistic cavity length of 300 μm and high-reflectivity coatings on both facets. The internal loss of the lasers was evaluated to be about 1.2 cm^-1 from the inclination of the plots between the external quantum efficiency and the cavity length. The ground-level modal gain per dot layer was evaluated to be 1.0 cm^-1, which closely agreed with the calculation taking into account the dot density, inhomogeneous broadening, and homogeneous broadening. The characteristic temperature of threshold currents T₀ was found to depend on cavity length and the number of dot layers in the active region of the lasers. A T₀ of 82 K was obtained near room temperature, and spontaneous emission intensity as a function of injection current indicated that the nonradiative channel degraded the temperature characteristics. A low-temperature study suggested that an infinite T₀ with a low threshold current (~1 mA) is available if the nonradiative recombination process is eliminated. The investigation in this paper asserted that the improvement in surface density and radiative efficiency of quantum dots is a key to the evolution of 1.3-μm quantum-dot lasers     

High-efficiency and high-power vertical-cavity surface-emittinglaser designed for cryogenic applications

We report the first AlGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) that has been optimized for cryogenic applications near 77 K, with superior characteristics that include a high-output power (P_out=22 mW at I=25 mA), high power conversion efficiency (ηd=32%), low threshold voltage (V_th=1.75 V) and current (I_th=1.7 mA), and low power dissipation (9 mW at P_out =2.0 mW) for a 20-μm-diameter device     

Threshold currents of 1.3-μm bulk, 1.55-μm bulk, and1.55-μm MQW DFB P-substrate partially inverted buried heterostructurelaser diodes

We investigate the threshold currents of 1.3-μm bulk, 1.55-μm bulk, and 1.55-μm multi-quantum-well (MQW) distributed feedback (DFB) P-substrate partially inverted buried heterostructure (BH) laser diodes experimentally and theoretically. In spite of the larger internal loss of the 1.55-μm bulk laser diodes, the threshold current of the 1.55-μm bulk DFB P-substrate partially inverted BH laser diode is almost the same as that of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diode. The experimentally obtained average threshold current of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diodes is 17 mA and that of the 1.55 μm bulk DFB P-substrate partially inverted BH laser diodes is 16 mA. The calculated threshold current of the 1.3-μm bulk DFB laser diode is 15.3 mA and that of the 1.55-μm bulk DFB laser diode is 18.3 mA, which nearly agree with the calculated values, respectively. We have fabricated two types of five-well 1.55-μm InGaAs-InGaAsP MQW DFB P-substrate partially inverted BH laser diodes. One has barriers whose bandgap energy corresponds to 1.3 μm, and the other has barriers of which bandgap energy corresponds to 1.15 μm. The calculated threshold current of the MQW DFB laser diode with the barriers (λ_g =1.3 μm) is 8.5 mA, which nearly agrees with the experimentally obtained value of 10 mA. However, the calculated threshold current of the MQW DFB laser diode with the barriers (λ_g=1.15 μm) is 7.9 mA which greatly disagrees with the experimentally obtained value of 19 mA, which suggests that the valence band discontinuity between the well and the barrier severely prevents the uniform distribution of the injected holes among five wells     

2.0-/spl mu/m single-mode operation of InGaAs-InGaAsP distributed-feedback buried-heterostructure quantum-well lasers

Distributed-feedback (DFB) buried-heterostructure (BH) lasers with quantum-well active region emitting at 2.0 /spl mu/m have been fabricated and characterized. The lasers with four wells showed performance of practical use: threshold current as low as 15 mA for 600-/spl mu/m-long devices and CW single-mode output up to 5 mW at 2.03 /spl mu/m under operation current of 100 mA were observed. The current- and temperature-tuning rates of DFB mode wavelength are 0.004 nm/mA and 0.125 nm/K, respectively.