The development of laser diode and other semiconductor light sources invoked the needs to the detectors of light. In this study, GaAs schottky diodes were fabricated and their photodetector applications were studied. The LPE system was characterized at the $800\,^\circ\!C$ liquidus temperature. By the use of the system, included the undoped layer. The edge growth effect and the meltback effect were analyzed in qualitative. GaAs schottky diodes were fabricated and their electrical and optical characteristics were examined. With buffer case, the forward electrical characteristics were superior to the diode without buffer layer. Typical diodes had the series resistance 10-20($\Omega$), the barrier height 0.76-0.82 eV etc.. By the LED driving circuit, the light detection characteristics were measured and compared to silicon p-i-n diodes. The improvement-of quantum efficiency is essential.