GROWTH AND FABRICATION OF HIGH-PERFORMANCE 980-NM STRAINED INGAAS QUANTUM-WELL LASERS FOR ERBIUM-DOPED FIBER AMPLIFIERS

A 980-nm strained InGaAs quantum-well (QW) laser is the preferred pump source for an Er3+-doped fiber amplifier for the next generation of l ightwave communication systems because of lower noise, high power conv ersion efficiency, and low temperature sensitivity. Obtaining long lif etime, narrow far field, high power output in the fundamental transver se mode centered at 980 +/- 5 nm, and planarity of the structure while maintaining low threshold current density (J(th)) and high differenti al quantum efficiency (eta) are the major challenges. Here, we report our work aimed at optimizing the design, growth, and fabrication of 98 0-nm lasers to address some of these issues. We demonstrate very low b road-area J(th) of 47 A . cm-2, operation up to 200-degrees-C, and a v ery low linewidth enhancement factor of 0.54 of these lasers. We have also monolithically integrated 980-nm lasers with 850-nm GaAs QW laser s. To minimize coincorporation of nonradiative recombination impuritie s like oxygen and displacement of the p/n junction due to Be diffusion during MBE growth, we suggest that the Be doping should be dispensed with on the p-side of the GRIN region and the n-side GRIN region shoul d be doped with Si. The optical properties of InGaAs QW's are insensit ive to the type of the arsenic beam used, As2 versus As4. Although str ained InGaAs QW lasers grown using As2 at a constant substrate tempera ture as low as 570-degrees-C have a lower J(th), they also exhibit a 1 0-25% lower eta as compared to the As4 counterpart in which the AlGaAs cladding layers are grown at approximately 700-degrees-C. To obtain a planar structure and to prevent the fabrication related defects, we h ave used a novel method in which the laser structure is first grown by MBE, and mesas are formed by in situ melt etching using SiO2 stripes as a mask followed by regrowth of p--p-n AlGaAs isolating layers by LP E. Compared to ridge waveguide (RWG) lasers, the buried heterostructur e lasers so fabricated have significantly lower threshold current, hig her power output, higher temperature operation, lower cavity losses, a nd kink-free light-current (L-I) characteristics, as expected. A CW po wer of 150 mW/facet at 986 nm was measured from a 400-mum-long BH lase r with 11-mum active stripe width. A minimum threshold current of 2.5 mA was measured for lasers with 3.0-mum active width and 300-400 mum c avity length. The L-1 characteristics of 500-, 800-, and 1300- mum-lon g lasers with 3.0-mum active width were linear up to the currents corr esponding to a current density of 10 kA . cm-2. At higher current dens ities, a sublinear increase of power with current was observed. Stable fundamental transverse mode operation was obtained up to 100-mW emitt ed power.