Comprehensive Schottky Barrier Height Behavior and Reliability Instability with Ni/Au and Pt/Ti/Pt/Au on AlGaN/GaN High-Electron-Mobility Transistors

Reliability Assessment of On-Wafer AlGaN/GaN HEMTs: The Impact of Electric Field Stress on the Mean Time to Failure

We present the mean time to failure (MTTF) of on-wafer AlGaN/GaN HEMTs under two distinct electric field stress conditions. The channel temperature (Tch) of the devices exhibits variability contingent upon the stress voltage and power dissipation, thereby influencing the long-term reliability of the devices. The accuracy of the channel temperature assumes a pivotal role in MTTF determination, a parameter measured and simulated through TCAD Silvaco device simulation. Under low electric field stress, a gradual degradation of IDSS is noted, accompanied by a negative shift in threshold voltage (ΔVT) and a substantial increase in gate leakage current (IG). Conversely, the high electric field stress condition induces a sudden decrease in IDSS without any observed shift in threshold voltage. For the low and high electric field conditions, MTTF values of 360 h and 160 h, respectively, were determined for on-wafer AlGaN/GaN HEMTs.

Impact of Charge-Trapping Effects on Reliability Instability in AlxGa1-xN/GaN High-Electron-Mobility Transistors with Various Al Compositions

In this study, we present a detailed analysis of trapping characteristics at the Al_xGa_1-xN/GaN interface of Al_xGa_1-xN/GaN high-electron-mobility transistors (HEMTs) with reliability assessments, demonstrating how the composition of the Al in the Al_xGa_1-xN barrier impacts the performance of the device. Reliability instability assessment in two different Al_xGa_1-xN/GaN HEMTs [x = 0.25, 0.45] using a single-pulse I_D-V_D characterization technique revealed higher drain-current degradation (∆I_D) with pulse time for Al_0.45Ga_0.55N/GaN devices which correlates to the fast-transient charge-trapping in the defect sites near the interface of Al_xGa_1-xN/GaN. Constant voltage stress (CVS) measurement was used to analyze the charge-trapping phenomena of the channel carriers for long-term reliability testing. Al_0.45Ga_0.55N/GaN devices exhibited higher-threshold voltage shifting (∆V_T) caused by stress electric fields, verifying the interfacial deterioration phenomenon. Defect sites near the interface of the AlGaN barrier responded to the stress electric fields and captured channel electrons-resulting in these charging effects that could be partially reversed using recovery voltages. The quantitative extraction of volume trap density (N_t) using 1/f low-frequency noise characterizations unveiled a 40% reduced N_t for the Al_0.25Ga_0.75N/GaN device, further verifying the higher trapping phenomena in the Al_0.45Ga_0.55N barrier caused by the rougher Al_0.45Ga_0.55N/GaN interface.

Ti3 C2 Tx MXene van der Waals Gate Contact for GaN High Electron Mobility Transistors

Gate controllability is a key factor that determines the performance of GaN high electron mobility transistors (HEMTs). However, at the traditional metal-GaN interface, direct chemical interaction between metal and GaN can result in fixed charges and traps, which can significantly deteriorate the gate controllability. In this study, Ti₃ C₂ T_x MXene films are integrated into GaN HEMTs as the gate contact, wherein van der Waals heterojunctions are formed between MXene films and GaN without direct chemical bonding. The GaN HEMTs with enhanced gate controllability exhibit an extremely low off-state current (I_OFF ) of 10^-7 mA mm^-1 , a record high I_ON /I_OFF current ratio of ≈10¹³ (which is six orders of magnitude higher than conventional Ni/Au contact), a high off-state drain breakdown voltage of 1085 V, and a near-ideal subthreshold swing of 61 mV dec^-1 . This work shows the great potential of MXene films as gate electrodes in wide-bandgap semiconductor devices.

Challenges and Opportunities for High-Power and High-Frequency AlGaN/GaN High-Electron-Mobility Transistor (HEMT) Applications: A Review

The emergence of gallium nitride high-electron-mobility transistor (GaN HEMT) devices has the potential to deliver high power and high frequency with performances surpassing mainstream silicon and other advanced semiconductor field-effect transistor (FET) technologies. Nevertheless, HEMT devices suffer from certain parasitic and reliability concerns that limit their performance. This paper aims to review the latest experimental evidence regarding HEMT technologies on the parasitic issues that affect aluminum gallium nitride (AlGaN)/GaN HEMTs. The first part of this review provides a brief introduction to AlGaN/GaN HEMT technologies, and the second part outlines the challenges often faced during HEMT fabrication, such as normally-on operation, self-heating effects, current collapse, peak electric field distribution, gate leakages, and high ohmic contact resistance. Finally, a number of effective approaches to enhancing the device's performance are addressed.

Explicit Thermal Resistance Model of Self-Heating Effects of AlGaN/GaN HEMTs with Linear and Non-Linear Thermal Conductivity

We presented an explicit empirical model of the thermal resistance of AlGaN/GaN high-electron-mobility transistors on three distinct substrates, including sapphire, SiC, and Si. This model considered both a linear and non-linear thermal resistance model of AlGaN/GaN HEMT, the thickness of the host substrate layers, and the gate length and width. The non-linear nature of channel temperature-visible at the high-power dissipation stage-along with linear dependency, was constructed within a single equation. Comparisons with the channel temperature measurement procedure (DC) and charge-control-based device modeling were performed to verify the model's validity, and the results were in favorable agreement with the observed model data, with only a 1.5% error rate compared to the measurement data. An agile expression for the channel temperature is also important for designing power devices and monolithic microwave integrated circuits. The suggested approach provides several techniques for investigation that could otherwise be impractical or unattainable when utilizing time-consuming numerical simulations.

A Novel AlGaN/GaN Transient Voltage Suppression Diode with Bidirectional Clamp Capability

This work proposes a novel AlGaN/GaN transient voltage suppression (TVS) diode (B-TVS-D) with bidirectional clamp capability, which consists of a small-size AlGaN/GaN monolithic bidirectional switch, two 2DEG-based current-limiting resistors (R_1A/R_1C, in parallel connection between the gate electrodes and the neighboring ohmic-contact electrodes (anode/cathode)), and a 2DEG-based proportional amplification resistor (R₂, in parallel connection between two gate electrodes). It is demonstrated that the proposed B-TVS-D possesses a symmetrical triggering voltage (V_trig) and a high secondary breakdown current (I_s, over 8 A, corresponding to 12 kV human body model failure voltage) in different directional electrostatic discharge (ESD) events. The proposed diode can effectively enhance the electrostatic discharge robustness for the GaN-based power system. It is also verified that R_1A/R_1C and R₂ have an important impact on V_trig of the proposed B-TVS-D. Both the decrease in R₂ and increase in R_1A/R_1C can lead to the decrease of V_trig. In addition, the proposed B-TVS-D can be fabricated on the conventional p-GaN HEMT platform, making the ESD design of the GaN-based power system more convenient.