DESIGN & FABRICATION OF 980NM WAVELENGTH QUANTUM WELL LASER

Abstract

A theoretical and experimental investigation of quantum well laser emitting at a wavelength of 980mn suitable for pumping Er3+ doped fiber amplifiers is carried out. The band structure, the TE and TM mode optical gains, and the radiative current density of the In. 0.2Ga. 0 8As/GaAs strained quantum well (70A well width) lasing at 980nm have been investigated using a 6x6 Hamiltonian model. The calculations are also extended to the quaternary InAlGaAs system. The results show that because of the compressive strain in the well region for both systems, the heavy hole does not couple with the light hole and the spin orbit splitting hole. The uppermost heavy-hole subbands exhibit good parabolicity. The calculated valence density of states is small and displays the almost ideal step-like behavior. The compressive strain also enhances the TE mode optical gain, and strongly depresses the TM mode optical gain at the same time. A very low threshold current density is predicted. These theoretical results are useful for the design and fmiher perfonnance improvement of the ternary and quaternary strained QW laser diodes. Stripe geometry and ridge waveguide quantum well lasers (3QW) have been fabricated from a graded index separate confinement heterostructure grown by molecular beam epitaxy. For a 4µm wide and 1000µm long ridge waveguide laser, a cw threshold current of 12.5mA, the threshold current density of 313A/cm2, an external quantum efficiency of 0.31mW/mA and power slope efficiency of 0.37mW/mA per facet were obtained. The emission wavelength, the high output power, and the fundamental lateral mode operation render these lasers suitable for pumping Er3 doped fiber amplifiers.