Schottky rectifiers fabricated on bulk GaN substrate analyzed by electron-beam induced current technique

We report the fabrication of specially-designed Schottky rectifiers with thin Schottky metal on bulk GaN substrate through a homoepitaxial process. The Schottky rectifiers show consistent easy turn-on behaviors but with a wide distribution of reverse leakage current levels. A turn-on voltage as low as 0.9V with a low on-resistance of 2.56mΩcm2 was obtained. The easy turn-on properties can be attributed to the low series resistance achieved by fabricating vertical geometry devices on highly conductive GaN substrate. Electron-beam induced current analysis indicates that although the dislocation density in the homo-epilayer is generally low and on the order of ∼1×107cm−2, mesoscopic defects such as grain boundaries and “dislocation walls” are present in the epilayer and serve as strong recombination centers. By comparing the reverse leakage current levels and the EBIC images of selected devices, we found that the “dislocation walls” observed are most likely to be the major source of high reverse leakage current. This study not only shows the promise of making high-performance GaN power devices based on homoepitaxial growth approach, but also indicates the importance of successful substrate polishing to the development of bulk-GaN-based devices.