Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

Abstract

Power electronic devices based on wide band-gap semiconductor materials such as GaN and SiC are rapidly being developed to replace traditional silicon-based devices whose performance has nearly reached their material limits. In the fabrication of GaN vertical power devices, selective area doping (SAD) processes are essential [1]. Several SAD techniques have been developed, including ion implantation [2], etching and regrowth method [3, 4], diffusion doping and neutron transmutation [5]. However, the influences of these procedures on the microstructures of GaN epitaxial layers is one of the key factors to determine the performance of the devices.In this study, ion-implanted GaN epitaxial layers from different stages including ammonothermal grown substrate material, metal organic chemical vapor deposition (MOCVD) epitaxial growth, ion implantation and subsequent annealing was characterized by synchrotron monochromatic beam X-ray topography (SMBXT) [6], synchrotron X-ray rocking curve topography (SXRCT) [7], and high-resolution X-ray diffraction (HRXRD). The change of distribution of threading dislocations (TDs) is characterized. The comparison of lattice strain of the material from each processing stage is conducted by both HRXRD and SXRCT.Enlarged contrast of screw and edge types of threading dislocations (TDs) on X-ray topographs after homoepitaxial growth is observed and likely due to interaction with point defects. X-ray topographs reveal ion implantation does not change the distribution of dislocations in the wafer. Strain and tilt maps derived from X-ray rocking curve topographs also show that annealing leads to an improvement in lattice bending levels. These results will be discussed with their implications for further processing into devices.