Ultrafast carrier dynamics in Schottky barriers is an extremely active area of research in recent years. The observation of the generation of terahertz pulses from metal/semiconductor interfaces provides a technique to characterize electronic properties of these materials. However, a detailed analysis of these phenomena has not been performed satisfactorily. In this work, the measurements of optically generated terahertz emission from Au/GaAs interfaces are investigated in detail. We observe that, under high laser power excitation, terahertz signals from bare GaAs wafers and Au/GaAs samples exhibit an opposite polarity. The polarity-flip behaviors in the terahertz beams are also observed in the temperature-dependent measurements and the femtosecond pump-generation studies of the Au/GaAs interfaces. These effects can be fully explained in terms of the dynamics of carrier transfer in the Au/GaAs Schottky barriers, which involves the internal photoelectric emission and the electron tunneling effect, and picosecond time constants are found for these processes.