Dislocation characterization of GaN layers in high-performance, High-Electron-Mobility Transistor structures grown on on-axis and off-axis 4H-SiC(0001) substrates

Abstract

Controlling the dislocation behavior in component layers is critical for fabricating high-performance, high-electron-mobility transistor (HEMT) devices. The dislocation characteristics in the gallium nitride (GaN) layers of HEMT structures grown on on-axis and off-axis 4H-SiC substrates via molecular beam epitaxy were studied using various X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. By employing high-resolution XRD and two-beam bright-field TEM images, the dislocation densities could be quantitatively analyzed, and the type of dislocations was identified in the GaN layers; the dislocation density on the off-axis substrate was higher than that on the on-axis substrate under the same deposition conditions, with a relative increase in the screw- and mixed-type dislocations identified in the GaN layer on the off-axis substrate. The evolution of screw- and mixed-type dislocations in an AlN buffer layer was also evident on the off-axis 4H-SiC substrate. Finally, the origin of the screw- and mixed-type dislocations was briefly demonstrated based on the atomic structures of the surface step of the off-axis 4H-SiC substrate. These findings provide valuable insights into the dislocation dynamics in GaN layers grown onto misoriented SiC substrates, contributing to the global effort to achieve superior HEMT performance through the optimization of epitaxial growth strategies.