The terahertz band (0.1 THz-10 THz) with massive spectrum resources is recognized as a promising candidate for future rate-greedy applications, such as 6G communications. Optoelectronic terahertz communications are beneficial for realizing 100 Gb/s data rate and beyond, which have greatly promoted the progress of the 6G research. In this article, we give technical insight into the key technologies of optoelectronic terahertz communications with high data rates in the physical layer, including approaches of broadband devices, baseband signal processing technologies, and design of advanced transmission system architectures. A multicarrier signal processing routine with high noise tolerance is proposed and experimentally verified in a 500 Gb/s net rate terahertz communication system. Finally, we discuss the future directions of optoelectronic terahertz technologies toward the target of terabit- scale communications.