In this work, we demonstrate that an organometallic perovskite (OP) single crystal for effective photodetection can be grown on a gold (Au)-decorated substrate using liquid phase epitaxy. The covered gold could both control the shape of the epitaxial layer and act as its electrodes. An MAPbCl₃ single crystal and an MAPbBr_1.5Cl_1.5 single crystal were used as the substrate and the epitaxial layer, respectively. The device, with an Au-perovskite-Au structure, can be fully characterized. Due to the high-quality epitaxial layer, the maximum external quantum efficiency (EQE) value is over 60% under the voltage of −20 V. In addition, the response speed can reach 200 and 500 ns (ns) rise and fall, respectively. Our work provides an effective and promising method to fabricate efficient perovskite-based photodetectors.