Imaging Nanoscale Electronic Changes in a Biased GaN HEMT

Abstract The transmission electron microscope (TEM) is the standard high-resolution technique for imaging microelectronics. But TEM primarily generates contrast related to the physical structure and composition of samples, giving little insight into their electronic properties. Samples must also be electron transparent, typically requiring cross-sectioning of components to nanometers-thin foils prior to imaging, which can compromise their electronic integrity. These cross section samples are also notoriously difficult to electrically connect to without surface leakage dominating transport. As a result, successful in situ electronic testing or bias-manipulation of electronic devices in the TEM is notably rare. Here we image nanoscale, bias-induced electronic changes in an electrically contacted cross section extracted from a GaN high electronmobility transistor (HEMT). The sample is prepared using a Xe+-based plasma focused ion beam (PFIB) to eliminate conducting implantation of the standard FIB ion, Ga+. Scanning TEM electron beam-induced current (STEM EBIC) imaging visualizes bias-induced changes to the device’s electronic structure during normal biasing, stressing, and after failure, all performed in situ.