Performance enhancement of MgZnO ultraviolet photodetectors using ultrathin Al₂O₃ inserted layer

In this study, the magnesium zinc oxide (MgZnO) films and ultrathin alumina (Al₂O₃) inserted layers were subsequently deposited on sapphire substrates using a plasma-enhanced atomic layer deposition system, and applied in metal-semiconductor-metal ultraviolet (UV) photodetectors (MSM-UPDs). The dark current of the MgZnO MSM-UPDs was decreased from 1 to 0.34 nA with an increase in Al₂O₃ layer thickness from 0 to 5 nm. The ultrathin Al₂O₃ inserted layer effectively passivated the dangling bonds on the MgZnO surface and blocked leakage current. At a bias voltage of 5 V, the maximum UV-visible rejection ratio of the MgZnO MSM-UPDs was 1.78 × 10³ with 5-nm-thick Al₂O₃ inserted layer. Furthermore, the noise equivalent power and detectivity of MgZnO MSM-UPDs with 5-nm-thick Al₂O₃ inserted layer were improved from 1.26 × 10^-14 W and 2.50 × 10¹³ cm Hz^1/2W^-1 to 0.93 × 10^-14 W and 3.40 × 10¹³ cm Hz^1/2W^-1 in comparison with MgZnO MSM-UPDs without Al₂O₃ inserted layer. The high performances of MgZnO MSM-UPDs were achieved by using ultrathin Al₂O₃ inserted layer.