We present a three-terminal gallium nitride (GaN)-based p-n diode capable of functioning as both a light emitter and detector. The device integrates a traditional p-n diode with a third terminal (Tt) composed of metal/Al2O3layers on the p-GaN layer. In emitter mode, the applied bias on the Tt modulates the energy band of the p-GaN layer, increasing bandwidth from 160 MHz to 263 MHz. As a detector, the TTD enables the configuration of optoelectronic logic gates (OELGs) such as NAND and NOR by adjusting the bias voltage at the p- and n-electrodes. This multifunctional design enhances performance and flexibility in optoelectronic applications.