Low-threshold JnGaAS/GaAS strained-layer quantum well lasers (X=O.98 n.m) with GaInP cladding layers grown by chemical beam epitaxy

Strained InGaAS/AIGaAS quantum well (QW) lasers operating at 0.98 jim are currently of great interest due to their suitability for pumping erbium-doped fiber amplifiers. They are reported to yield a lower noise figure and higher gain coefficient than the 1 .48 jim InGaAsflnP pump lasers as well as 0.8 p.m A1GaAS/GaAS pump lasers. In addition, the InGa.AS/AIGaAS strained QW lasers have lower threshold current, higher slope efficiency, and less temperature dependance. All these factors contribute to lowering the power dissipation of the pump design. Recently Ga0.511n0.49P, lattice-matched to GaAs has been introduced as a substitute for the AIGaAS cladding layers due to reports suggesting its resistance to rapid degradation by dark line defect propagation and to catastrophic mirror damage. The aluminium-free system also lends itself more readily to device fabrication by selective etching and epitaxial regrowth or mass transport We report on the first InGaAS/Ga.AS strained-layer QW lasers using GaInP cladding layers grown by chemical beam epitaxy. The laser structure is a separate confinement heterostructure (SCH) with the active region consisting of 70 A thick InO.2GaO.8As quantum wells and 220 A thick GaAs barriers. The active and the SCH region are cladded by Ga0.5 lInO.49P layers of 1.35 p.m thickness. A very low broad-area threshold current density of 70 A/cm2 was obtained for 1500 p.m long single QW lasers which is among the lowest reported for InGaAS/GaAS/GaInP lasers. The Jth for two and three QW lasers were 135 A/cm2 and 170 A/cm2 respectively. Ridge waveguide lasers with 4 p.m width have very low cw threshold currents: 7.8 mA for 500 p.m-long cavity and 10 mA for 750 p.m-long cavity. External differential quantum efficiency as high as 0.9 mW/mA was obtained for 250 p.m-long lasers. From the slope of inverse quantum efficiency versus cavity length, a very low internal waveguide loss of 2.5 cm-l and an internal quantum efficiency of 0.95 are inferred.