High power and high efficiency operation of Al-freeInGaAs/GaInAsP/GaInP GRINSCH SQW lasers (λ≃0.98 μm)

High power and high quantum efficiency Al-free InGaAs/GaInAsP/GaInP GRINSCH SQW lasers emitting at 0.98 μm are reported. A CW output power as high as 580 mW and single lateral mode power up to 280 mW were achieved for the Al-free ridge waveguide lasers at room temperature. The lasers exhibited a high internal quantum efficiency of 99% and low internal waveguide loss of 3.2 cm^-1. A high characteristic temperature of 217 K and low threshold current density of 109 A/cm² were also obtained. The results are the best obtained for Al-free 0.98 μm pumping lasers     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

Fabrication of short GaAs wet-etched mirror lasers and theircomplex spectral behavior

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-μm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm²) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH2     

Circular beam emission from 1.3 μm InGaAsPstrained-multiquantum-well lasers

The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3-μm InGaAsP strained MQW lasers     

Dry-etched wire distributed feedback laser

We report on the realization and the properties of dry-etched wire and wire-DFB lasers and compare them with two-dimensional (2-D) reference lasers. The starting vertical structure, which was optimized for low threshold, consists of four GaInAs quantum wells embedded in a GaInAsP waveguide. Even for very small longitudinal confinement factors of the order 0.23, the dry-etched wire lasers show laser operation up to 60°C and a threshold current density at room temperature of 5 kA/cm ² for simple oxide stripe lasers. For the wire lasers, an increase of the differential material gain of more than one order of magnitude (about a factor of 20) was measured, compared to conventional 2-D lasers. The wires were also arranged periodically with different grating constants to allow gain-coupled DFB laser operation. Clear single-mode emission has been found, as expected, from the gain-coupling mechanism     

Room temperature CW operation ofGa0.3In0.7As/GaInAsP/InP strained MQW lasers withwire active region

A room temperature CW operation of Ga_0.3In_0.7As/GaInAsP/InP GRINSCH compressive strained MQW lasers with 30~60 nm wide wire active region was achieved. This device was fabricated by two-step LP-OMVPE growths on p-type InP substrate and wet chemical etching. Threshold current as low as 53 mA ( L=910 μm, J_th=2.9 kA/cm²) was obtained at RT-CW condition. The spontaneous emission peak and the lasing wavelength of strained MQW wire lasers exhibited approximately 20-meV blue shift from those of MQW film lasers cut out from the same wafer     

Room-temperature pulsed operation of triple-quantum-well GaInNAslasers grown on misoriented GaAs substrates by MOCVD

The lasing operation of three-quantum-well GaInNAs stripe geometry lasers grown by MOCVD on 0° and 6° misoriented (100) GaAs substrates, respectively, have been demonstrated and their performance is compared for the first time. Both devices achieved room temperature, pulsed lasing operation at an emission wavelength of 1.17 μm, with a threshold current density of 667 A/cm² for lasers grown on 6° misoriented substrates, and 1 kA/cm² for lasers grown on 0° misoriented substrates. The threshold for the lasers grown on 6° misoriented substrates compares favorably with the best results for GaInNAs lasers. Lasers with narrower stripe width and a planar geometry have also been demonstrated by the use of lateral selective wet oxidation for current confinement, with a threshold current density of 800 A/cm² for 25-μm-wide devices     

Very low threshold current densities (under 100 A/cm2) in AlGaAs/GaAs single-quantum-well GRINSCH lasers grown by molecular beam epitaxy

Threshold current densities as low as 80 A/cm2 for 3.3 mm-long cavity lasers, and 93 A/cm2 for 520 ?m-long cavity lasers have been obtained in AlGaAs/GaAs graded-index separate-confinement heterostructure (GRINSCH) single-quantum-well lasers with quantum-well widths between 65?165 A grown by molecular beam epitaxy. The structures were prepared on (100) GaAs substrates and do not display the earlier reported dependence of lasing threshold characteristics on the quantum-well thickness in the range studied (65?165 A).     

Electrically pumped circular-grating surface-emitting DBR laser onInGaAs strained single-quantum-well structure

The authors demonstrate the fabrication and room temperature operation of an electrically pumped circular-grating surface-emitting distributed-Bragg-reflector laser. An InGaAs/GaAs single quantum well (SQW) graded-index separate confinement heterostructure (GRINSCH) structure was grown by one-step molecular beam epitaxy (MBE). Circular gratings were defined by focused ion beam lithography. The lasing wavelength was 942 nm, and the threshold current was 280 mA. This is the first demonstration of these lasers with no epitaxial regrowth     

The effect of increased valence band offset on the operation of 2μm GaInAsSb-AlGaAsSb lasers

Two and four quantum-well (QW) GaInAsSb-AlGaAsSb lasers emitting at 2 μm are reported. In comparison to previously published data, it is found that higher Al content in the QW barrier improves the internal efficiency, saturated modal gain, and characteristic temperature of the lasers. These results are attributed to an increased valence band offset that provides superior hole confinement in the GaInAsSb QW. A differential efficiency of 74% is observed at 25°C under pulsed conditions for a 900-μm cavity length, 2-QW device, and a record characteristic temperature of 140 K is measured for a 4-QW laser     

High-temperature characteristics of 1.3-μm InAsP-InAlGaAs ridgewaveguide lasers

High-temperature characteristics of InAsP-InAlGaAs strained multiquantum-well (MQW) lasers with a large conduction band discontinuity (ΔE_c) are demonstrated. The InAsP-InAlGaAs MQW ridge waveguide lasers with narrow stripes exhibited a characteristic temperature as high as 143 K in the range from 25°C to 85°C. This material system is promising for developing a cooling-system-free 1.3-μm laser     

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     

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     

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     

GaxIn1-xAsyP1-y-InPtensile-strained quantum wells for 1.3-μm low-threshold lasers

Ga_xIn_1-xAs_yP_1-y-InP tensile-strained multiple quantum wells (MQWs) grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) are studied for the application to 1.3-μm lasers. High-resolution X-ray diffraction curves show good agreement with theoretical simulation. Clear energy separation of light hole and heavy hole bands is observed in the room temperature photoluminescence measurement. Threshold characteristics of -1.15% tensile-strained MQW lasers with graded index separate confinement heterostructure (GRINSCH) are investigated. The minimum threshold current density per well (J_th/N_w) for infinite cavity length obtained is 100 A/cm² for the device with a well number of 3. Tensile strain dependence of J_th/N _w for an infinite cavity is also clarified     

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     

Ridge formation for AlGaAs GRINSCH lasers by Cl2reactive ion etching

Optical storage applications for AlGaAs power lasers require single-mode laser operation and well-controlled beam divergence. For AlGaAs GRIN separate confinement heterostructure (GRINSCH) ridge lasers, these optical characteristics are sensitive to the precise ridge geometry of the laser. Directional reactive ion etching with Cl₂ and in situ monitoring of the etch with highly attenuated laser interferometry provide the excellent process control required during formation of the ridge. The process is described, and results are presented for lasers that were fabricated using this technique     

Long-wavelength InP-based quantum-dash lasers

Self-assembled InAs quantum-dash (QD) lasers with emission wavelengths between 1.54 and 1.78 μm based on the AlGaInAs-AlInAs-InP material system were grown by gas source molecular beam epitaxy. Threshold current densities below 1 kA/cm² were achieved for 1-mm-long mirror coated broad area lasers with a stack of four QD layers. The devices can be operated up to 80°C in pulsed mode and show a high T₀ value of 84 K up to 35°C. In comparison to quantum-well lasers a much lower temperature sensitivity of the emission wavelength was achieved. The temperature shift of Δλ/ΔT = 0.12 nm/K is as low as that caused by the refractive index change     

Well-thickness dependence of high-temperature characteristics in1.3-μm AlGaInAs-InP strained-multiple-quantum-well lasers

Well-thickness dependence of temperature characteristics of 1.3-μm AlGaInAs-InP strained-multiple-quantum-well lasers was investigated. Higher characteristic temperatures of threshold current density were obtained for thicker wells up to 6 nm. Fabricated ridge-waveguide lasers with 6-nm-thick wells exhibited characteristic temperature of as high as 125 K. Relaxation-oscillation frequency reduced by only 13% between 25°C and 85°C     

Preliminary reliability studies of 1.55 mu m graded index separate confinement buried heterostructure (GRINSCH) multiple quantum well (MQW) lasers grown by metalorganic vapour phase epitaxy (MOVPE)

1.55 mu m graded index separate confinement heterostructure (GRINSCH) multi-quantum-well (MQW) lasers, grown entirely by metalorganic vapour phase epitaxy (MOVPE), have demonstrated low degradation rates in lifetests at 50 degrees C, 4 mW per facet. These lasers are complex structures, containing many interfaces, and the encouraging early lifetest results demonstrate the ability of MOVPE to grow these structures.<>