Photoelectrochemical Etching Technology for Gallium Nitride Power and RF Devices

Photoelectrochemical (PEC) etching was used to fabricate deep trench structures in GaN-on-GaN epilayers grown on n-GaN substrates. The width of the side etching was less than 1 mu m, with high accuracy. The aspect ratio (depth/width) of a 3.3-mu m-wide trench with a PEC etching depth of 24.3 mu m was 7.3. These results demonstrate the excellent potential of PEC etching for fabricating deep trenches in vertical GaN devices. Furthermore, we simplified the PEC etching technology to permit its use in a wafer-scale process. We also demonstrated simple contactless PEC etching technologies for the manufacture of power and RF devices. A trench structure was fabricated in a GaN-on-GaN epilayer by simple contactless PEC etching. The role of the cathodic reaction in contactless PEC etching is discussed in relation to the application of a GaN HEMT epilayer on a semi-insulating substrate. Fortunately, the GaN HEMT structure contains an ohmic electrode that can act as a cathode in contactless PEC etching, thereby permitting the recess etching of a GaN HEMT epilayer grown on a semi-insulating SiC substrate. These results indicate that PEC etching technologies are becoming suitable for use in the fabrication of practical GaN power and RF devices.