Very low threshold current density room temperature continuous-wavelasing from a single-layer InAs quantum-dot laser

Continuous-wave (CW) lasing operation with a very low threshold current density (J_th=32.5 A/cm²) has been achieved at room temperature by a ridge waveguide quantum-dot (QD) laser containing a single InAs QD layer embedded within a strained InGaAs quantum well (dot-in-well, or DWELL structure). Lasing proceeds via the QD ground state with an emission wavelength of 1.25 μm when the cavity length is longer than 4.2 mm. For a 5-mm long QD laser, CW lasing has been achieved at temperatures as high as 40°C, with a characteristic temperature T₀ of 41 K near room temperature. Lasers with a 20 μm stripe width have a differential slope efficiency of 32% and peak output power of >10 mW per facet (uncoated)     

Continuous-wave operation of long-wavelength quantum-dot diodelaser on a GaAs substrate

Continuous-wave operation near 1.3 μm or a diode laser based on self-organized quantum dots (QD's) on a GaAs substrate is demonstrated. Multiple stacking of InAs QD planes covered by thin InGaAs layers allows us to prevent gain saturation and achieve long-wavelength lasing with low threshold current density (90-105 A/cm²) and high output power (2.7 W) at 17°C heatsink temperature. It is thus confirmed that QD lasers of this kind are potential candidates to substitute InP-based lasers in optical fiber systems     

150-nm tuning range in a grating-coupled external cavityquantum-dot laser

An antireflection (AR) coated single-stack quantum-dot (QD) laser in a grating-coupled external cavity is shown to operate across a tuning range from 1.095 μm to 1.245 μm. This 150-nm range extends from the energy levels of the ground state to excited states. At any wavelength, the threshold current density is no greater than 1.1 kA/cm ². This large tunable range is the product of the rapid carrier filling of the higher energy states under a low pumping current and homogeneous broadening in the QD ensemble. The possibility of a larger tuning range is discussed with the further improvement of the AR-coating     

Low threshold current density 1.3-μm strained-layer quantum-welllasers using n-type modulation doping

We have developed 1.3 μm n-type modulation-doped strained-layer quantum-well lasers. Modulation-doped lasers with long cavities (low threshold gain) exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 250 A/cm² for 1500 μm long lasers with five quantum wells. The estimated threshold current density for an infinite cavity length was 38 A/m²/well. This is the lowest value for InGaAsP-InGaAsP and InGaAs-InGaAsP quantum well lasers to our knowledge     

Low threshold current density operation of GaInNAs quantum welllasers grown by metalorganic chemical vapour deposition

A metal organic chemical vapour deposition grown GaInNAs quantum well laser emitting at 1.25 μm is reported. The lowest threshold current density obtained by 50 μm wide stripe lasers was 340 A/cm² for a cavity length of 1420 μm. Which is almost comparable to the lowest value reported for GaInNAs lasers grown by molecular beam epitaxy. The threshold current density per well was 170 A/cm², which is the lowest threshold value reported to date     

Engineering laser gain spectrum using electronic vertically coupled InAs-GaAs quantum dots

Continuous large-broad laser gain spectra near 1.3 /spl mu/m are obtained using an active region of electronic vertically coupled (EVC) InAs-GaAs quantum dots (QDs). A wide continuous electroluminescence spectrum, unlike that from conventional uncoupled InAs QD lasers, was obtained around 230 nm (below threshold) with a narrow lasing spectrum. An internal differential quantum efficiency as high as 90%, a maximum measured external differential efficiency of 73% for a stripe-length of L=1 mm, and a threshold current density for zero total optical loss as low as 7 A/cm/sup 2/ per QD layer were achieved.     

Low threshold current density operation of GaInAsP-InP laser withmultiple reflector microcavities

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm² (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 μm and the cavity width of 200 μm     

High-power GaInAsSb-AlGaAsSb multiple-quantum-well diode lasersemitting at 1.9 μm

High-power diode lasers emitting at ~1.9 μm have been fabricated from a quantum-well heterostructure having an active region consisting of five GaInAsSb wells and six AlGaAsSb barriers. For devices 300 μm wide and 1000 μm long, single-ended output power as high as 1.3 W cw has been obtained with an initial differential quantum efficiency of 47%. The pulsed threshold current density is as low as 143 A/cm² for 2000-μm-long devices     

High performance CW 1.26 μm GaInNAsSb-SQW and 1.20 μmGaInAsSb-SQW ridge lasers

Long-wavelength GaInNAsSb SQW lasers and GaInAsSb SQW lasers that include small amounts of Sb have been successfully grown by gas-source molecular beam epitaxy (GSMBE) and processed into ridge lasers. The GaInNAsSb lasers oscillated under CW operation at 1.258 μm at room temperature. A low CW threshold current of 10.2 mA and high characteristic temperature (T₀) of 146 K were obtained for the GaInNAsSb lasers which is the best result for GaInNAs-based narrow-stripe lasers. Furthermore. The GaInAsSb lasers oscillated under CW operation at 1.20 μm at room temperature. A low CW threshold current of 6.3 mA and high characteristic temperature (T₀) of 756 K were obtained for the GaInAsSb lasers, which is also the best result for the 1.2 μm-range of highly strained GaInAs-based narrow-stripe lasers     

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     

Continuous wave operation of optically pumped membrane DFB laser

Room-temperature, continuous-wave operation of a 1.55 μm wavelength GaInAsP/InP membrane distributed feedback laser consisting of deeply etched single-quantum-well wire-like active regions is demonstrated under optical pumping. A threshold power of 38 mW was obtained for a 10.7 μm wide and 40 μm long device. A large stop-band width of 65 nm and a low equivalent refractive index of 2.30, which are inherent in a thin membrane waveguide structure, were observed     

InGaAs quantum dot lasers with submilliamp thresholds and ultra-lowthreshold current density below room temperature

Continuous-wave operation of InGaAs quantum dot lasers is studied. A very low threshold current of 460 μA is achieved at 200 K for a 5 μm×1170 μm oxide-confined stripe laser. For a larger stripe width of 11 μm, a threshold current density of 5.2A/cm² is demonstrated. The characteristic threshold temperature is -700 K in the temperature range of 14-200 K, and drops rapidly around room temperature     

The performances of (InAs)1/(GaAs)2short-period superlattice strained single-quantum-well laser on GaAssubstrate

We fabricated an (InAs)₁/(GaAs)₂ short-period superlattice (SPS) strained quantum-well laser at 1.07 μm by MOVPE. The SPS active layer has 10 periods of (InAs)₁/(_GaAs)₂ and an average mismatch of over 2.2%. In highly strained conditions the device showed a lasing wavelength of 1.07 μm, a threshold of 130 A/cm², and a characteristic temperature T₀ of 175 K. We measured the gain characteristic by the Hakki and Paoli method at LED conditions and obtained a high differential gain of 2.0×10^-15 cm² at the threshold current     

Temperature dependence of lasing characteristics forlong-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Data are presented on the temperature dependence of 1.3-μm wavelength quantum-dot (QD) lasers. A low-threshold current density of 90 A/cm² is achieved at room temperature using high reflectivity coatings. Despite the low-threshold current density, lasing at the higher temperatures is limited by nonradiative recombination with a rapid increase in threshold current occurring above ~225 K. Our results suggest that very low threshold current density (⩽20 A/cm ²) can be achieved at room temperature from 1.3-μm QD lasers, once nonradiative recombination is eliminated     

1.5 μm λ/4 shifted multiple quantum well distributedfeedback laser diodes

1.5 μm λ/4 shifted multiple quantum well distributed feedback laser diodes have been achieved for the first time. A characteristic temperature value for a threshold current at around room temperature was as high as 88 K. Spectra at 0.9 times the threshold current showed substantial TM mode suppression. The MQW active region consists of four GaInAs wells (75 Å thick) and GaInAsP barriers (λ_g=1.15 μm, 150 Å thick) grown by metalorganic vapour phase epitaxy (MOVPE). 1.3 μm GaInAsP was grown as an optical guide layer     

Vertical integration of a GaAs/AlGaAs quantum-well laser and along-wavelength quantum-well infra-red photodetector

A short-wavelength (~0.8 μm) GaAs/AlGaAs graded-index separate-confinement heterostructure quantum-well laser has been monolithically integrated with a long-wavelength (~8 μm) GaAs/AlGaAs multiple-quantum-well infra-red photodetector on a semi-insulating GaAs substrate by molecular beam epitaxy. The vertical integration method is used and the combined structure is a pinin structure. Both the laser and detector exhibit excellent characteristics. At room temperature, the ridge waveguide laser has an extremely low threshold current of 25 mA and a differential quantum efficiency above 65% with a stripe width of 20 μm. The quantum-well detector has a peak response at 8 μm and a responsivity of 0.7 A/W     

Visible AlGaAs single quantum well lasers with low thresholdcurrent density grown by molecular beam epitaxy

The letter reports short wavelength emission (7205 Å) from MBE AlGaAs GRINSCH single quantum well lasers. Visible emission is obtained with a 60 Å AlGaAs well containing ≃18% aluminium and both design optimisation and growth conditions lead to low-threshold operation. Broad area Fabry-Perot diodes have threshold current densities as low as 390 A/cm² and 670 A/cm² for cavity lengths of 500 μm and 250 μm, respectively     

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     

Multiwavelength InGaAs/InGaAsP strained-layer MQW-laser array usingshadow-masked growth

A simple technique for fabricating multiwavelength laser arrays is presented. The lateral variations in bandgap (or emission wavelength) between the different lasers are obtained by the use of shadow-masked growth. The shadow masked growth results in variations in thickness (and to a lesser extent, in composition) over the substrate. In combination with a multiquantum well (MQW) active region, this gives the required bandgap variations. By varying the window width in the shadow mask between 10 μm and >500 μm it was possible to obtain a wavelength span of 130 nm centered around 1.55 μm. The strained-layer-ridge MQW Fabry-Perot lasers showed a constant threshold current (around 70 mA for an 11-μm×500-μm stripe)     

Analysis of semiconductor microlasers with an equilateral triangleresonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with a side length of about 5 μm, we find that single fundamental mode operation at about 1.55 μm can be obtained as the side length increases from 4.75 to 5.05 μm. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA