Local Electric Field Measurement In Gan Diodes By Exciton Franz-Keldysh Photocurrent Spectroscopy

The eXciton Franz-Keldysh (XFK) effect is observed in GaN p-n junction diodes via the spectral variation of photocurrent responsivity data that redshift and broaden with increasing reverse bias. Photocurrent spectra are quantitatively fit over a broad photon energy range to an XFK model using only a single fit parameter that determines the line shape and the local bias (V-l), uniquely determining the local electric field maximum and depletion widths. As expected, the spectrally determined values of V-l vary linearly with the applied bias (V) and reveal a large reduction in the local electric field due to electrostatic non-uniformity. The built-in bias (V-bi) is estimated by extrapolating V-l at V = 0, which, when compared with independent C-V measurements, indicates an overall 60.31V accuracy of V-l. This demonstrates sub-bandgap photocurrent spectroscopy as a local probe of electric field in wide bandgap diodes that can be used to map out regions of device breakdown (hot spots) for improving electrostatic design of high-voltage devices. Published under license by AIP Publishing.