Search

V-gate GaN high-electron-mobility transistors (HEMTs) are fabricated and investigated systematically. A V-shaped recess geometry is obtained using an improved Si3N4 recess etching technology. Compared with standard HEMTs, the fabricated V-gate HEMTs exhibit a 17% higher peak extrinsic transconductance due to a narrowed gate foot. Moreover, both the gate leakage and current dispersion are dramatically suppressed simultaneously, although a slight degradation of frequency response is observed. Based on a two-dimensional electric field simulation using Silvaco "ATLAS" for both standard HEMTs and V-gate HEMTs, the relaxation in peak electric field at the gate edge is identified as the predominant factor leading to the superior performance of V-gate HEMTs.

Direct current (DC) and pulsed measurements are performed to determine the degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas (2DEG). The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.

A new multilayer-structured AlN/AlGaN/GaN heterostructure high-electron-mobility transistor (HEMT) is demonstrated. The AlN/AlGaN/GaN HEMT exhibits the maximum drain current density of 800 mA/mm and the maximum extrinsic transconductance of 170 mS/mm. Due to the increase of the distance between the gate and the two-dimensional electron-gas channel, the threshold voltage shifts slightly to the negative. The reduced drain current collapse and higher breakdown voltage are observed on this AlN/AlGaN/GaN HEMT. The current gain cut-off frequency and the maximum frequency of oscillation are 18.5 GHz and 29.0 GHz, respectively.

This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors. It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device. The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail. Under the ON-state stress, the strong electric-field led to degradation of SiNx passivation located in the gate-drain region. As the thickness of SiNx passivation increases, the density of the surface state will be increased to some extent. Meanwhile, it is found that the high NH3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.

The current slump of different recipes of SiNx passivated AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. The dc and pulsed current-voltage curves of AlGaN/GaN HEMTs using different recipes are analyzed. It is found that passivation leakage has a strong relationship with NH3 flow in the plasma-enhanced chemical vapor phase deposition process, which has impacted on the current collapse of SiNx passivated devices. We analyze the pulsed IDS – VDS characteristics of different recipes of SiNx passivation devices for different combinations of gate and drain quiescent biases (VGS0, VDS0) of (0, 0), (−6, 0), (−6, 15) and (0, 15)V. The possible mechanisms are the traps in SiNx passivation capturing the electrons and the surface states at the SiNx/AlGaN interface, which can affect the channel of two-dimensional electron gas and cause the current collapse.

Three kinds of metal-oxide-semiconductor high-electron-mobility transistors （MOS-HEMTs） with different thickness of Al2O3 dielectric layer were fabricated on the same wafer by atomic layer deposition. The measurement results of MOS capacitance，gate leakage current，and the output and transfer characteristics indicate that the control capability of the gate on two-dimentional electron gas will be reduced，while the gate leakage current will be decreased and the breakdown voltage will be increased with the increase of the Al2O3 dielectric layer thickness. Our analysis shows that the thinner the dielectric layer is，the greater the gate capacitance will be，which leads to greater negative shift of threshold voltage and much poorer insulating performance in restraining gate leakage current. Otherwise，with the increase of dielectric layer，higher gate voltage will be applied to obtain higher maximum saturation current density. Moreover，a thorough analysis of the transconductance and the capacity-voltage （C-V） characteristic shows that better passivation effect and insulating performance can be obtained with thicker dielectric layers.