Electrochemical Behavior of Ga3+, NO3
- and NH4
+ Ions and Electrodeposition of GaN in Aqueous Solutions
Authors: Kang Jaewook , Kuroda Kensuke , Okido Masazumi 
Published: February 2020

Gallium nitride (GaN) is one of the most interesting III-V semiconductor materials because its direct wide band gap (3.39 eV) at room temperature, which has a wide use in optical devices operating at blue and ultraviolet wavelengths, and its promising potential for semiconductor optical and electronic devices, which are suitable for high temperature, high power, and high-frequency applications. In the last few decades, many studies have been reported on the growth of GaN thin films using various techniques such as metalorganic chemical vapor deposition (MOCVD), reactive molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE), etc. However, these require very expensive equipment and well-defined environments, such as ultra-high vacuum and high temperature. Therefore, we can think of an economical electrodeposition as an effective way to replace existing methods. Electrodeposition is very economical and environment-friendly method compared to previous techniques because it is very simple to use and can synthesize materials at room temperature. Therefore, a simple and inexpensive electrodeposition technique was adopted for the synthesis of GaN film in this study.

For the synthesis of GaN, gallium nitrate (Ga(NO3)3) and gallium chloride (GaCl3) were used as gallium sources, and ammonium nitrate (NH4NO3) and ammonium chloride (NH4Cl) were selected as nitrogen sources. Prior to deposition, cyclic voltammetry analysis was performed to check the electrochemical behavior of each ion in the solution. An n-type silicon wafer was used as a working electrode and a platinum coil was used as a counter electrode. The reference electrode was an Ag|AgCl|KCl. The pH of all solutions was adjusted to 1.5. To unify the ion species present in the bath, hydrochloric acid (HCl) was used to adjust the pH of the solutions containing GaCl3 or NH4Cl, and nitric acid (HNO3) was used for the solutions containing Ga(NO3)3 or NH4NO3 severally. The voltammogram was obtained from the solution containing one reagent each, and then compared with the graphs obtained from the mixed solution.

The results revealed that nitrate ion (NO3
-) can be changed to other state (NO3
- → NO2
- → NH4
+) and a reduction peak of gallium was also confirmed in the solution. Therefore, it was considered that GaN can be synthesized on the Si substrate if the reduction reaction of gallium ions occurs between the steps of changing nitrate ions.

The electrodeposition to synthesis GaN was carried out at current densities of 8 mA/cm2 for 6 h in mixed solutions containing Ga(NO3)3, and NH4NO3. The deposited GaN film showed a plate-like structure, and gallium, nitrogen and oxygen were uniformly present in this film. The presence of GaN film was also supported by XRD analysis. Photoluminescence showed that our sample exhibit blue luminescence and also confirmed the peaks are in good agreement with the band gap energy of GaN. Photoluminescence showed that the deposits exhibits a blue luminescence and also a peak is in good agreement with the band gap energy of GaN.