Blocking Si‐Induced Visible Photoresponse in n‐MgxZn1–xO/p‐Si Heterojunction UV Photodetectors Using MgO Barrier Layer

Photodetectors based on n‐Mg0.25Zn0.75O/p‐Si heterojunctions are not only suitable for integration with existing semiconductor technology, but also circumvent the difficulty of stable p‐type doping in MgxZn1–xO. However, the use of Si leads to photoresponse in the visible part of the light spectrum, which renders n‐MgxZn1–xO/p‐Si heterojunction devices unsuitable for visible blind UV photodetection. Herein, it is demonstrated that the visible photoresponse in the n‐Mg0.25Zn0.75O/p‐Si photodetectors can be significantly suppressed by inserting a thin interlayer of MgO at the heterojunction. The MgO layer serves as a blocking layer for the drift of photo‐excited electrons from p‐Si to n‐Mg0.25Zn0.75O, thereby limiting the visible photoresponse. It is found that on increasing the thickness of the MgO interlayer from 3 to 15 nm, the UV to visible rejection ratio increases from ≈25 to 200. This enhancement in the UV to visible rejection ratio demonstrates that n‐Mg0.25Zn0.75O/p‐Si heterojunction devices with MgO interlayer are promising for visible‐blind UV photodetection applications. The visible photoresponse in n‐Mg0.25Zn0.75O/p‐Si heterojunction could be significantly reduced by inserting a MgO barrier layer between the p‐Si substrate and the Mg0.25Zn0.75O film. The visible light suppression is caused by the presence of a high conduction band offset at the p‐Si/MgO interface that works as a barrier for the drift of the visible excited electrons from the p‐Si to n‐Mg0.25Zn0.75O.