Electrochemical Etching of n-type GaN in Different Electrolytes

Nanosized pores were introduced into GaN epitaxial films via electrochemical (EC) anodic etching in strong electrolytes including NaOH, HNO3, NaNO3, and NaCl. The growth behaviors of GaN nanopores show a strong correlation with the electrolyte types under the same applied bias and electrolyte concentration. Specifically, the resulting morphologies (e.g. pore growth direction and pore size) were mainly pertinent to the anions instead of cations. Pore sizes as small as a few nanometers and pore directions between the horizontal and vertical directions can be adjusted by selecting the electrolytes and etching voltages. The depletion model was employed to interpret the carrier flow pathways, and the pore propagation direction can be regarded as the sum of etch rate vectors of intended etching direction and preferential oxidation direction. Finally, the near-infrared nanoporous (NP) GaN distributed Bragg reflectors (DBRs) were manufactured by the EC etching in different electrolytes. Our study points out that the type of anions in electrolyte greatly impacts pore morphologies of EC etched GaN:Si, thereby affecting the future applications.