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

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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 ηd 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 ηd 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.