Elsevier

Results in Materials

Volume 15, September 2022, 100290
Results in Materials

Ohmic-Schottky conversion of ZnO/metal contact modulated by a plasma surface treatment method

https://doi.org/10.1016/j.rinma.2022.100290Get rights and content
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Highlights

  • The study shows that the Ar and N2 plasma treatment can hardly improve the ZnO/Au Schottky contact performance, while the conversion from Ohmic type to Schottky type can be realized by the O2 plasma treatment.

  • After the treatment by the O2 plasma, the rectification ratio of the In/ZnO/Au device reached as high as 30250 and the corresponding Schottky barrier height was determined as high as 0.93 eV.

  • The O2 plasma treatment may play two key roles within the contact conversion: 1, removing the surface contaminants; 2, repairing the defects (Vo).

Abstract

Herein, we present a systematical investigation with regard to the Ar/N2/O2 plasma surface treatments on the ZnO thin films prepared by a radio frequency plasma-assisted molecular beam epitaxy (RF MBE) technique. The as-deposited ZnO thin films are exposed to the Ar, N2 and O2 plasma atmospheres under different RF powers. The conductivity and the surface morphology of the post-treated ZnO thin films are strongly depending on the treatment species and the RF powers. Higher RF power results in lower resistance and reduces the grain boundaries of the surface. Indium and gold metals are designed as the Ohmic and Schottky contact electrodes, respectively. The ZnO/Au contacts based on both pre-treated films and Ar/N2 plasma-treated films show obvious Ohmic contact behaviors. However, In/ZnO/Au the devices fabricated on the ZnO thin film which exposes to the O2 plasma show distinct rectified behavior, indicating the conversion of ZnO/Au contact from Ohmic type to Schottky type. The O2 plasma treatment may play two key roles within the contact conversion: 1, removing the surface contaminants such as carbon, absorbed oxygen and hydroxide; 2, repairing the defects (Vo), thus reducing the near surface donor density and defect assisted hopping transportation.

Keywords

ZnO
Surface treatment
Ar/N2/O2 plasma
Ohmic-Schottky conversion

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