Room-temperature continuous-wave operation of large-area (120 ,m X 980 ,um) GaAs/AlGaAs graded-refractiveindex separate-confinement heterostructure lasers on (100) Si substrates has been obtained. Minimum threshold- as a test of material quality.14 Dislocations, strain, and other defects present in the material, however, have kept the threshold-current densities high and limited the measurements to pulsed conditions. In this Letter we present results on extremely lowthreshold current lasers and the first report to our knowledge of continuous wave (cw) operation of a GaAs/AlGaAs/Si injection laser at room temperature. The epitaxial structures were grown by molecularbeam epitaxy (MBE) on (100) Si tilted by 4° toward (110). The substrate cleaning procedure and growth conditions used were similar to those of Ref. 5. The graded-refractive-index separate-confinement heterostructure laser consisted of a 7-nm quantum-well, 350-nm parabolic graded region and a 1.5-,um cladding AlGaAs layer on each side of the confining structure.

Me V oxygen ion implantation in GaAs/ AlGaAs has been shown to provide a simple and very promising technique for quantum well laser fabrication. A lOµm stripe single quantum well (SQW) graded-index separation confinement heterostructure (GRINSCH) laser made in this way has achieved high performance with high quantum differential efficiency, low threshold current and good electrical isolation characteristics. MeV oxygen ion implantation with optimum thermal annealing produces a deep buried electrical isolation layer in n-type GaAs and reduces optical absorption in GaAs/ AlGaAs quantum well structures. Ion implantation stimulated compositional disordering as well as implanted oxygen-related deep level traps may be considered as important effects for electrical and optical modification of interfaces in GaAs and AlGaAs.

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