A graded-index waveguide separate-confinement laser with very low threshold and a narrow Gaussian beam

A heterostructure semiconductor laser with graded-index waveguide and separate carrier and optical confinements prepared by molecular beam epitaxy is discussed. These lasers have very low broad-area threshold current densities Jth 500 A/cm2 and support narrow beams of Gaussian distribution with far-field half-power full-width in the direction perpendicular to the junction plane ϑ⊥ ∼20°–30°. It is also shown that only when the active layer thickness is ≲700 Å a significantly lower Jth is obtained by employing the symmetric laser structure instead of the regular double heterostructure.