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 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 gallium nitride (GaN)-based high-electron-mobility transistors at a sub-micron resolution. To illustrate the capabilities of the approach, we used it to examine the impact of carbon impurity in the epitaxial buffer layer of the 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, despite similar device terminal characteristics, very different electric field distributions can occur in devices with different carbon concentration. We also show that dislocation related leakage paths can lead to inhomogeneity in the electric field