Poole-Frenkel electron emission from the traps in AlGaN/GaN transistors

Defect-related localized electronic states in AlGaN/GaN transistors give rise to commonly observed charge trapping phenomena. Electron emission from the trapping centers is strongly affected by electric field, which can exceed values of 10 MV/cm during device operation. The field-assisted emission characteristics provide a unique way to determine the physical properties of the trapping centers. We present a detailed study of the effects of electric field and temperature on the rate of electron emission from the barrier traps in AlGaN/GaN high electron mobility transistors. We demonstrate, that for temperatures above 250 K, the Poole-Frenkel (PF) emission is the dominant mechanism for electrons to escape from the trapping centers. The emission rate increases exponentially with the square root of the applied field consistent with the decrease of the apparent activation energy predicted by the PF model. We find that the observed trapping center is described the attractive long-range Coulomb potential with the zero-field binding energy of ~0.5 eV.