Low Threshold Current Density and High Efficiency Surface‐Emitting Lasers with a Periodic Gain Active Structure

We have achieved very low threshold current densities with high light output powers for InGaAs / GaAs surface‐emitting lasers using a periodic gain active structure in which three quantum wells are inserted in two‐wavelength‐thick (2λ) cavity. Air‐post type devices with a diameter of 20~40 μ m exhibit a threshold current density of 380~410 A/cm 2 . Output power for a 40 μ m diameter device reaches over 11 mW. A simple theoretical calculation of the threshold and power performances indicates that the periodic gain structure has an advantage in achieving low threshold current density mainly due to the high coupling efficiency between gain medium and optical field. The deterioration of power, expected from the long cavity length of 2λ, is negligible.