Using MgO capping layer to enhance the performance of ZnO based metal-semiconductor-metal photodetectors

Magnesium oxide (MgO) was deposited on zinc oxide (ZnO) surface to achieve a visible-blind ultraviolet (UV) metal-semiconductor-metal photodetectors (MSM-PDs). ZnO and MgO were prepared using a radio-frequency (RF) magnetron sputtering system. As compared to the MSM-PDs without the MgO capping layer, the dark current is greatly subdued by approximately four orders of magnitude in the MSM-PDs with MgO capping layer, which in turn largely increases the photo/dark current ratio from 10 2 to 10 5 by three orders in the MSM-PDs. The MgO capping layer enhances the ultraviolet/visible rejection ratio and largely raised the detectivity from 8.3 × 10 10 to 1.03 × 10 12 Jones in the prepared MSM-PDs. X-ray photoelectron spectroscopy shows that the oxygen vacancies on ZnO surface were compensated by the introduced oxygen atoms from MgO, forming a stable film that passivated the ZnO surface. The MgO capping layer greatly increases the Schottky barrier height (SBH) of an Au/ZnO Schottky barrier diode (SBD) from 0.58 to 0.93 eV for the Au/MgO/ZnO SBD. The raised SBH and suppressed surface defects drastically reduced the dark current and visible response of the prepared MSM-PDs.