Electrochemical fabrication and interfacial charge-transfer process of Ni/GaN(0001) electrodes

Abstract

The electrodeposition of Ni on single-crystal n-GaN(0001) film from acetate solution was investigated using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, atomic force microscopy, and electrochemical techniques. The as-deposited Ni/n-GaN(0001) had a flat band potential of U_fb = −1.0 V vs. Ag/AgCl, which was much lower than that of bare GaN(0001). That is, a more feasible charge-transfer process occurred at the Ni/n-Ga(0001) interface. On the basis of a Tafel plot, an exchange current density of ∼1.66 × 10⁻⁴ mA cm⁻² was calculated. The nuclei density increased when the applied potential was varied from −0.9 V to −1.2 V and, eventually the whole substrate was covered. In addition, the current transient measurements revealed that the Ni deposition process followed instantaneous nucleation in 5 mM Ni(CH₃COO)₂ + 0.5 M H₃BO₃.