Zhang Yamin

Evaluation of the drain—source voltage effect on AlGaAs/InGaAs PHEMTs thermal resistance by the structure function method

The effect of drain—source voltage on AlGaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that AlGaAs/InGaAs PHEMTs thermal resistance presents a downward trend under the same power dissipation when the drain—source voltage (VDS) is decreased. Moreover, the relatively low VDS and large drain—source current (IDS) result in a lower thermal resistance. The chip-level and package-level thermal resistance have been extracted by the structure function method. The simulation result indicated that the high electric field occurs at the gate contact where the temperature rise occurs. A relatively low VDS leads to a relatively low electric field, which leads to the decline of the thermal resistance.

Self-heating and traps effects on the drain transient response of AlGaN/GaN HEMTs

The effects of self-heating and traps on the drain current transient responses of AlGaN/GaN HEMTs are studied by 2D numerical simulation. The variation of the drain current simulated by the drain turn-on pulses has been analyzed. Our results show that temperature is the main factor for the drain current lag. The time that the drain current takes to reach a steady state depends on the thermal time constant, which is 80 μs in this case. The dynamics of the trapping of electron and channel electron density under drain turn-on pulse voltage are discussed in detail, which indicates that the accepter traps in the buffer are the major reason for the current collapse when the electric field significantly changes. The channel electron density has been shown to increase as the channel temperature rises.

Influence of gold particle size on melting temperature of VLS grown silicon nanowire

Based on the Lindemann melting model, a model related to gold nanoparticle size and melting temperature for VLS grown silicon nanowire is proposed. Eutectic temperatures of Au–Si with different gold sizes have been calculated using the model and are in agreement with the experimental results. This model has been demonstrated to be reasonable, and it can be used to determine the growth temperature of silicon nanowire.

Mechanism of the self-changing parameters and characteristics in AlGaN/GaN high-electron mobility transistors after a step voltage stress*

The phenomenon of self-changing on the device parameters and characteristics after a step voltage stress was applied to the gate is studied in AlGaN/GaN high electron mobility transistors. The device was measured every 5 min after the stress was removed. The large-signal parasitic source (drain) resistance, transfer characteristics, threshold voltage, drain-source current, gate-source (drain) reverse current-voltage characteristics changed spontaneously after the removal of the stress. The time constant of the self-changing was about 25-27 min. The gate-source (drain) capacitance-voltage characteristics were constant during this process. Electrons were trapped by the surface states and traps in the AlGaN barrier layer when the device was under stress. The traps in the AlGaN barrier layer then released electrons in less than 10 s. The surface states released electrons continuously during the entire measurement stage, leading to the self-changing of mearsurement result.