Comparison of InAs quantum dot lasers emitting at 1.55 μm under optical and electrical injection

InAs/InGaAsP/InP(I 13)B quantum-dots are studied as active mediums for laser structures emitting near 1.55 mu m under optical and electrical injection. In order to precisely tune the emission wavelength of QDs, the double cap growth procedure is used. Laser emission on the ground states is obtained under optical pumping at room temperature. On equivalent structures doped for electrical injection, laser emission is also observed at low temperatures up to 200 K. The difference between the optical and electrical pumping is ascribed to low carrier injection efficiency due to the presence of a 3 nm InP hole blocking barrier at each quantum dot layer which is inherent to the double cap growth procedure. Room temperature laser emission has been reached when the InP first cap layer is substituted by a quaternary GaInAsP (1.18 mu m gap) layer in the double cap growth procedure. The threshold current density of the new structure with QD capped only by quaternary is as low as 840 A cm(-2) at room temperature.