Indium phosphide-based strained multiple quantum well lasers.

Abstract

Strained quantum well lasers have been the objects of intense research in the recent literature. In GaAs, strained lasers are important as optical pumping sources in solid state lasers and fiber amplifiers. The ultra-low-loss and low-dispersion fibers available at 1.55 $\mu$m have stimulated interest in lasers which operate at this wavelength. The InGaAs/InP/InGaAsP system is ideal for a study of the effects of tensile and compressive strain. The ability of chemical beam epitaxy (CBE) to grow high quality bulk material and heterointerfaces has facilitated the isolation and study of the effects of strain on the characteristics of InP-based multiple quantum well-separate confinement heterostructure (MQW-SCH) lasers. High-resolution photoluminescence measurements have been made on undoped InGaAsP alloys grown by CBE. The luminescent efficiency of the samples is a strong function of the growth temperature. The samples are characterized by bound exciton peaks in the edge luminescence and the samples grown at low temperatures (530$\sp\circ$C) show the presence of impurity-related peaks. MQW-SCH lasers have been grown in the InGaAsP/InP/In$\sb{x}$Ga$\sb{1-x}$As system $(0.33\le x\le 0.73)$ and their static and dynamic characteristics studied. We show that strain has a significant effect on device performance. Differential gains are measured for the first time as a function of strain and are roughly double their lattice-matched values in both the tensile and compressive cases. Threshold current densities as low as 589 A/cm$\sp2$ have been measured for devices with 800 $\mu$m cavities. Modulation bandwidths as high as 5 GHz have been observed for devices with 10% excess In. The impact of strain on the Auger coefficient has also been explored for the first time. The Auger coefficient increased from $5\times10\sp{-30}cm\sp6/s$ at lattice match to $12.5\times10\sp{-3}cm\sp6/s$ for devices with 20% excess In. Laser characteristics have been calculated for the In compositions investigated experimentally. A degenerate k $\cdot$ p formalism has been employed along with the deformation potential theory to calculate the bandstructures of the InGaAs quantum wells. The gain and spontaneous emission rates were then calculated and the coupled rate equations solved. Comparison between theoretical and experimental data yielded good agreement.