Improving the performance of Al/MgO/NiO Schottky-barrier photodetectors using a MgO intermediate layer with introduced oxygen

This study employs magnetron sputtering to sandwich a MgO intermediate layer between Al and NiO for fabricating Al/MgO/NiO Schottky-barrier photodetectors. Two different MgO films are prepared for comparison: during sputtering, one MgO film without introduced oxygen and the other MgO film with introduced oxygen. The effects of the oxygen introduced in MgO on the performance of the Schottky-barrier photodetectors are studied. The Al/NiO Schottky-barrier photodetectors without the MgO intermediate layer exhibits the highest dark current due to the surface defects of NiO. After the MgO was sandwiched between Al and NiO, the dark current is observed to decrease. In the Al/MgO/NiO Schottky-barrier photodetectors for MgO without introduced oxygen, the dark current is suppressed by only one order of magnitude. By contrast, the dark current is drastically reduced by approximately 5000 times in the Al/MgO/NiO Schottky-barrier photodetectors for MgO with introduced oxygen. This is because the introduced oxygen atoms compensate for the oxygen vacancies of MgO. This result increases the on/off ratio by approximately 3000 times and enhances detectivity from 5.4 x 1010 to 2.5 x 1012 Jones in the Al/NiO and Al/MgO/NiO with introduced oxygen, respectively, by approximately 50 times. X-ray photoelectron spectroscopy shows that the number of lattice oxygen atoms increases from 30.5 % to 52.1 % for the MgO films without and with introduced oxygen, respectively. The carrier transport mechanism reveals only one ohmic conduction in Al/NiO and Al/MgO/NiO without introduced oxygen, where the carriers tunnel through the metal/semiconductor interface via the surface defects of NiO and MgO, respectively. However, the Al/MgO/NiO with introduced oxygen appears two distinct regions. For V <= 0.4 V, the space-chargelimited current controls the conduction; however, for V >= 0.4 V, the Schottky emission dominates carrier transport.