Low Threshold Current InP-Based Strained-Layer 1.55µm Lasers

Abstract

The internal strain resulting from lattice mismatch between thin active layers and a thick substrate can confer considerable advantages to long wavelength laser characteristics. With sufficient built-in strain, the highest hole band has a low effective mass and is well separated from the lower bands. The low effective mass reduces the areal carrier density needed for population inversion and leads to the virtual elimination of two important loss mechanisms: Auger recombination and intervalence band absorption. We consider a separate confinement heterostructure laser with strained InGaAs wells, grown on an InP sub-strate. This structure promises easier growth and greater stability than structures considered earlier. The valence band structure is calculated using the Luttinger-Kohn 6x6 Hamiltonian in the axial approximation. The threshold current density is of 220Åcm^-2 at room temperature, nearly an order of magnitude lower than conventional 1.55μm lasers. Furthermore, we predict an increased temperature stability, of advantage for long wavelength optical communication applications.