LAUSR

The metal–semiconductor–metal (MSM) structure is widely applied in photodetectors (PDs) owing to its simple preparation method and a more effective light collecting area. However, the realization of weak light detection remains a daunting challenge, attributed to the low external quantum efficiency (EQE) in MSM‐based PDs. Herein, sandwich structure PD (SSPD), a new structure of PD based on MSM structure, is presented to solve the problem of low gain in MSM PDs. Herein, the high‐EQE MgZnO/Au/ZnO SSPD with avalanche effect is reported for the first time. The avalanche effect is realized by changing the position of electronic transmission through energy band engineering between MgZnO and ZnO in the sandwich structure. The SSPD exhibits high EQE when photogenerated carriers get transported at the interface of ZnO and MgZnO. Under 275 nm illumination, the MgZnO/Au/ZnO SSPD achieves avalanche multiplication at 63 V and shows EQE of up to 502780% at 90 V. These results reveal that a high EQE originates from the special sandwich structure existing in MgZnO/Au/ZnO SSPD. This study presents possible guidance for high‐performance ZnO‐based avalanche PD for applications in telecommunications, sensing, and single‐photon detection.