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 during ID versus V-GS dc 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 on V-DS and V-GS and requires to be suitably addressed in compact models. Finally, data concerning trapping effects consequent to the application of RF signal are discussed.
Deep-Level Effects in Back-Barrier-Scaled GaN HEMTs
De Pieri F.;Carlotto A.;Fregolent M.;Cavaliere A.;Saro M.;Rampazzo F.;De Santi C.;Meneghesso G.;Meneghini M.;Zanoni E.
2026
Abstract
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 during ID versus V-GS dc 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 on V-DS and V-GS and requires to be suitably addressed in compact models. Finally, data concerning trapping effects consequent to the application of RF signal are discussed.
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