GaAlAs/GaAs Surface Emitting Laser with High Reflective TiO2/SiO2 Multilayer Bragg Reflector

Abstract

First, it has been made clear that the important parameters of the SE laser are its active layer thickness d and the mirror reflectivity R. The required values of three parameters such as threshold gain g _th, threshold current density J _th, and differencial quantum efficiency η_d are obtained for d=2∼3 µm and R=95%. At this condition g _th is estimated as 300 cm^-1 (N _th=3×10¹⁸ cm^-3), J _th is 25∼30 kA/cm², and η_d is 40%. Next, in order to obtain a reflectivity as high as 95%, a TiO₂/SiO₂ multilayer Bragg reflector was introduced. It was found that a good quality TiO₂ film could be evaporated by leaking oxygen through a variable leak valve to hold 1×10^-4 Torr. Then, a 7-pair TiO₂/SiO₂ multilayer Bragg reflector was fabricated; its peak reflectivity was 95% at 8800 Å. A room-temperature pulsed operation of a GaAlAs/GaAs SE layer was achieved and the minimum threshold current was reduced to as low as 150 mA when a round mesa was fabricated to 20 µm in diam.