Consideration on threshold current density of GaInAsP/InP surface emitting junction lasers

The oscillation condition of the GaInAsP/InP surface emitting (SE) junction laser ( m) is examined. Theoretical calculations indicate that reflectivity of the mirrors of a Fabry-Perot resonator is necessary to be 95 percent for a reasonably low threshold current density. Then, we have fabricated a new structure for SE laser and compared its threshold current density with the theoretical estimation. In order to maintain the necessary reflectivity without deteriorating the ohmic contact, we adopted a ring electrode where the reflecting mirror is separated from the -side electrode. The threshold current was reduced down to 35 mA at 77 K which is 70 percent of the early experiment. The threshold current density was estimated to be 5 kA/ cm². The estimated reflectivity was 80-85 percent. The operating temperature has been raised to -21°C (252 K). The temperature dependence of the threshold current near room temperature suggests that room temperature operation of GaInAsP/InP SE lasers is possible by increasing the reflectivity of mirrors and current confinement.