Threshold Voltage Instability in D-mode AlGaN/GaN MIS-HEMTs with Al2O3 Gate Dielectric

In this paper, D-mode MIS-HEMTs with 24 nm ALD-Al2O3 gate dielectric are studied. The electrical parameters, such as threshold voltage (Vth), drain current (Ids), on-resistant (Ron), sub-threshold swing (SS), and gate leakage current (Ileak) are investigated during the gate stress phase and recovery phase at room temperature. It is found that, during the stress phase, Vth and Ron show positive shifts while Ids show negative shifts. It is because channel electrons are trapped by the dielectric/III-nitride interface layer and by the bulk traps in the gate dielectric. However, these electrical parameter changes cannot be fully recoverable at the end of the recovery phase, followed by 30 mins thermal de-trapping. It may be caused by (1) positive gate bias induced unrecoverable defects in the dielectric layer. (2) bulk trap has a relatively large emission constant. (3) AlGaN barrier exists between the channel and dielectric/III-nitride interface layer, make the electrons hard to exchanges.