No abstract

A new method for extraction of bias-dependent source and drain resistances in AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) is reported. The total source/drain access resistances are extracted by measuring the pulsed transfer characteristics of test devices with various quiescent biases. With short pulse width, the charge trapping and thermal effects will not be affected by the magnitude of pulse voltages, and thus the extracted resistances correspond to the quiescent bias condition. As a result, the dependences of total access resistances on the gate and drain voltages are obtained. While employing the dual-sweep combinational transconductance technique, the source and drain resistances are separated further. To investigate the variation of access resistances with applied voltages, AlGaN/GaN HEMTs are also illuminated with a 365-nm ultraviolet (UV) source during pulsed measurements. Under UV illumination, the resistance will be less dependent on the drain voltage, indicating the charge trapping in GaN buffer layer has a large impact on the access resistance.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.