| dc.description.abstract | GaN Nitride material has many superior properties, such as high electron mobility, high critical electric field, and high saturation velocity. It is especially suitable for 5G base stations and low-orbit satellites requiring high-output power. However, defects generated in the epitaxial crystallization process of gallium nitride could cause reliability issues under high-current and high-voltage operations. The current dispersion effect will cause the drain output current to decrease, which will seriously affect the accuracy of the device modeling and limit the device’s output power. In this study, the commercial WIN gallium nitride device is adopted to investigate the change of current transient. Applying different off-state stress and on-state voltage to observe the changes in current transient. The on-state voltage can be divided into linear and saturation regions to compare. When the device switches from the off-state to the on-state linear region, the temperature dependence of the de-trapping is observed, and it is thermally activated with trap activation energy around EA=0.5 eV. On the contrary, temperature-dependent detrapping is hard to observe when the device switches from the off-state to the on-state saturation region. It is speculated that the possible reason is that there is a higher electric field between the drain and the source, which makes it easier for the electric field-assisted tunneling effect to occur.
In addition, this thesis also proposes a pulsed small signal S-parameter measurement method. After the off-state stress voltage is applied to the device, the S-parameter is measured with a short pulse turn-on voltage. The changes in the small signal parameters are observed when current dispersion occurs. The equivalent circuit model is established and extracts small signal parameters. It can be observed that when the device is turned off with a high drain bias, the intrinsic parameters such as the resistance between the drain and the source (Rds), the capacitance between the gate and the drain (Cgd), and the capacitance between the drain and the source (Cds) all change significantly. The electrons in the channel may be trapped by defects in the AlGaN barrier layer and buffer layer under a high electric field. | en_US |