Gate current leakage and breakdown mechanism in unpassivated AlGaN∕GaN high electron mobility transistors by post-gate annealing

Abstract

Gate leakage/breakdown mechanism in unpassivated AlGaN∕GaN high electron mobility transistors (HEMTs) is investigated by performing temperature-dependent pulsed current–voltage (I–V) and current transient measurements of AlGaN∕GaN HEMTs without and with annealing after Schottky gate formation. After post-gate annealing, the devices exhibited significantly smaller gate leakage current and higher breakdown voltage even without any gate dielectrics or passivation layer. The temperature-dependent current transient measurements show that the current dispersion in the unannealed HEMTs is attributed to traps with an emission time constant (tE) of ∼0.5μs at 295 K and an activation energy of ∼38meV. On the contrary, the 20-min annealed devices have traps with tE of 21.6μs at 295 K and an activation energy of ∼0.31eV. The results suggest that the post-gate annealing removes shallow traps, and creates or activates deeper traps. We propose that the breakdown and gate leakage current is mainly due to the emission current from shallow traps in unpassivated AlGaN∕GaN HEMTs. The breakdown voltage improvement after the post-gate annealing is due to the removal of shallow traps near the Schottky gate metal∕AlGaN interface.

High-Voltage AlGaN/GaN High-Electron-Mobility Transistors Using Thermal Oxidation for NiOxPassivation

“…The conventional device exhibited a similar amount of current for both the drain-pulsed and the gate-and-drain-pulsed I-V. It was reported that the conventional AlGaN/GaN HEMT has shallow traps with activation energy levels below 38 meV [10]. The pulse duration of 5 µs is long enough to emit from a shallow state.…”

“…The reaction process of Ni and O in the AlGaN barrier may be related to the formation of deep states. It has been reported that the deep states suppress the leakage current due to their low emission rate [9,10]. We also measured test samples oxidized at 300 and other samples oxidized at 700 °C.…”

“…The proposed device sustained a low leakage current until breakdown. The oxidation process can form deep states which suppress the gate leakage current [9,10]. The deep states as a result of the oxidation process are explained by the subsequent pulsed I-V.…”

“…SiO 2 passivation [8,9] reportedly improves the blocking characteristics of high-voltage switches. Post-annealing [10] or oxidation [11] methods have also been proposed to improve the breakdown voltage and gate leakage current. NiO x has been studied as a p-type ohmic contact in GaN light-emitting diodes [12].…”

“…In an effort to address these surface problems, various passivation methods [6][7][8][9] and surface treatments [9][10][11][12] have been studied. Si 3 N 4 passivation [6,7] has widely used to suppress the RF dispersion in microwave applications.…”