Computers, despite their apparent complexity, are essentially composed of numerous electronic switches that toggle on and off in a specific sequence to process digital information. The advancements in semiconductor technology have enabled the creation of smaller and faster switches. One such promising material is gallium nitride (GaN), which facilitates high-speed movement of charge carriers like electrons. This property makes GaN valuable in high electron-mobility transistors (HEMTs) used in applications such as mobile phone chargers, 5G base stations, radar systems, and satellite communications.
Optimizing the functionality of HEMTs requires efficient electrical connections that control the switching of transistors. These connections, called Schottky gates, sometimes suffer from high leakage currents that persist even when the transistor is in the off state. Consequently, this leads to increased power consumption and limits the voltage tolerance of the device before it malfunctions.
Researchers from Xiaohang Li’s and Husam Alshareef’s teams, in collaboration with scientists from India and China, have demonstrated a method to mitigate these limitations by utilizing a class of materials called MXenes for constructing Schottky gates. MXenes are two-dimensional, atomically thin layers of metallic transition metal carbides, nitrides, or carbonitrides. The study detailing their findings has been published in the journal Advanced Materials.
While conventional metals have conventionally been employed as electrical contacts for GaN, the interaction between these metals and GaN can lead to defects that trap electrical charge, thereby impeding gate control. Chuanju Wang from Li’s team explains that the traditional metal gate contact materials are typically deposited using methods like electron-beam evaporation and sputtering, which form a direct chemical bond with the semiconductor substrate.
Wang further elaborates, “We demonstrated that our two-dimensional MXene establishes a van der Waals contact with the semiconductor substrate, which significantly reduces interface traps and fixed charges.”
The team from KAUST successfully fabricated a GaN HEMT with a gate contact composed of clean films of the MXene Ti3C2Tx. Their device exhibited an off-state current of only 10^-7 milliamps per millimeter, which is approximately 10^13 times smaller than the current when the HEMT is in the on state. This on-off ratio represents a significant improvement of six orders of magnitude compared to devices employing more conventional nickel-gold contacts.
Wang states, “The next step is to employ MXenes as Schottky-gate contact materials in other types of transistors, such as Ga2O3, In2O3, NiO, and AlN.”
Alshareef expresses his pride in Chuanju and Xiangming for their innovative thinking and hard work, emphasizing their substantial contributions to the project’s success.