Low-threshold injection InGaAsP/GaAs double heterostructure lasers with separate limiting obtained by liquid-phase epitaxy (lambda = 0.78 divided by 0.87 microns, I sub thr = 460 A/cm 2, T = 300 K)

Low-threshold infrared and red separate-limited double heterostructure lasers based on InGaAsP/GaAs structures with active region thickness d d sub o = 0.1+0.03 micron, prepared by ordinary liquid-phase epitaxy, are described. The devices employ additional waveguide layers of InGaAsP between the narrow-zone active region and the wide-zone emitters. The active region is 2 to 10/6 micron thick, with the total thickness of the waveguide lasers comprising 0.4 micron. A minimum threshold of 460 A/sq cm (T = 300 K) is obtained for four-layer specimens. Continuous lasing is obtained at room temperature in lasers not employing strip designs. The drop in thresholds in double heterostructure lasers with separate limiting results from the fact that the absolute threshold current densities continue to drop as d becomes smaller in the region d d sub o, in spite of the near-linear drop in r = f(d).