Electric field mapping of wide-bandgap semiconductor devices at a submicrometre resolution

Electric fields drive the degradation of wide-bandgap semiconductor devices. However, directly mapping the electric field inside an active device region remains challenging. Here we show that electric-field-induced second harmonic generation can be used to map the electric field in the device channel of GaN-based high-electron-mobility transistors at submicrometre resolution. To illustrate the capabilities of the approach, we use it to examine the impact of carbon impurities in the epitaxial buffer layer of a device. Carbon is a p dopant in GaN, and small changes in its concentration can dramatically change the bulk Fermi level, sometimes resulting in a floating buffer that is ‘short-circuited’ to the device channel via dislocations. Our measurements show that very different electric field distributions can occur in devices with different carbon concentrations, despite them having similar device terminal characteristics. We also show that dislocation-related leakage paths can lead to inhomogeneity in the electric field.