LOW-THRESHOLD 1.5 MICRO-M COMPRESSIVE-STRAINED MULTIPLE-QUANTUM-WELL AND SINGLE-QUANTUM-WELL LASERS

Design considerations for making low-threshold 1.5-mu-m 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 (2 nm thick) is analyzed and compared between the separate-confinement heterostructure (SCH) and the step graded-index separate-confinement heterostructure (GRIN-SCH). Experimentally, 1.5-mu-m 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-mu-m oxide stripe width. Using a short cavity together with high-reflection facet coatings, submilliampere-threshold planar buried heterostructure (PBH) lasers in the 1.5-mu-m wavelength region were achieved.