Deep-Level Effects in Back-Barrier-Scaled GaN HEMTs

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Drain current transient spectroscopy is adopted to study deep-level effects in scaled GaN high electron mobility transistors (HEMTs) and to identify trap time constants in different bias conditions, needed for the definition of compact circuit-level models including dispersion effects. Fe- and C-doped reference devices are compared to devices adopting AlGaN back-barriers or buffer-free devices where the GaN channel was grown directly on the AlN nucleation layer. We identified an acceptor trap at the GaN/back-barrier interface (Ea = 0.7–0.9 eV) common to both back-barrier and buffer-free devices. This trap is correlated with an overshoot of the transconductance,gₘ, due to sudden trap ionization and negative threshold voltage shift occurring duringIDversusVGSdc measurements. We demonstrate that the electron detrapping mechanism is photoionization, due to bremsstrahlung radiation emitted by the devices in hot-electron regime. When bias is applied during the recovery phase emission rate increases by several orders of magnitude. This makes traps time constants heavily dependent onVDSandVGSand requires to be suitably addressed in compact models. Finally, data concerning trapping effects consequent to the application of RF signal are discussed.