Investigation of surface treatment schemes on n-type GaN and $Al0.20Ga0.80N$

The effects of $SiCl4$ reactive-ion-etching (RIE) plasma treatment on $n-GaN$ and $n-Al0.20Ga0.80N$ surfaces, and the subsequent cleaning of the surfaces using ammonium hydroxide $(NH4OH)$⁠, hydrochloric acid (HCl), and buffered oxide etch (BOE) solutions, have been investigated using x-ray photoelectron spectroscopy and Auger electron spectroscopy measurements. Of these cleaning schemes, BOE was found to be the most effective treatment to remove oxides from the surfaces of the $SiCl4$ plasma treated samples. The $SiCl4$ plasma treatment of GaN and AlGaN resulted in the blueshift of Ga–N $(Ga3d)$ peaks to higher binding energies corresponding to a shift of the Fermi level $(EF)$ toward the conduction band edge at the surface. It has been reported that this type of shift is caused by the creation of N vacancies, which act as $n$-type dopant [D. W. Jenkins and J. D. Dow, Phys. Rev. B. 39, 3317 (1989); M. E. Lin, Z. F. Fan, Z. Ma, L. H. Allen, and H. Morkoç, Appl. Phys. Lett. 64, 887 (1994); A. T. Ping, Q. Chen, J. W. Yang, M. A. Khan, and I. Adesida, J. Electron. Mater. 27, 261 (1998)] on the surface due to $SiCl4$ plasma treatment. This corresponds to an increase in $n$-type dopant density on the surface. Thus, $SiCl4$ plasma treatment in a RIE system thins the Schottky barrier heights of $n-GaN$ and $n-AlGaN$ and aids in the formation of ohmic contacts on such surfaces.