Improving Material Quality of Polycrystalline GaN by Manipulating the Etching Time of a Porous AlN Template

Abstract

A porous template has been reported to reduce defect density and strains, and hence to improve the properties of gallium nitride (GaN) deposited on it. On the other hand, creating a porous aluminum nitride (AlN) template is challenging and, therefore, reports on it are scarce. In this work, the material quality of a polycrystalline GaN layer was improved by manipulating the etching time of the porous AlN template. The porous AlN template was fabricated for 5 and 30 min by ultraviolet (UV)-assisted sodium hydroxide (NaOH)-based electrochemical etching. The 5-min-etched porous AlN template exhibited a better uniformity of the pore distribution than the 30-min-etched porous AlN template. A non-porous AlN was also prepared for a comparison. All samples had gallium oxide (Ga2O3) inclusions in the polycrystalline GaN due to the oxide layer formation during the AlN template etching. However, such inclusions have been successfully removed by dipping the porous AlN template in hydrofluoric acid (HF) solution prior to the GaN layer deposition. Next, the polycrystalline GaN layer was deposited on both templates by an electron beam (e-beam) evaporator, followed by a thermal annealing treatment to promote better crystalline structure. The polycrystalline GaN layer that was deposited on the 5 min-etched porous AlN template showed a good uniform distribution of grains with lower surface roughness and smaller x-ray diffraction (XRD) full-width half maximum (FWHM) compared to other conditions. In addition, the 5-min-etched porous AlN template also showed better electrical properties than its counterparts, which justifies the use of this process for electronic devices.