Material considerations for the design of 2D/3D hot electron transistors

Combining two- and three-dimensional (2D/3D) materials provides a unique route to enabling next-generation hot electron transistors (HETs)—a vertical ballistic device, promising for high-frequency applications since they are not limited by electron velocity saturation, fabrication limitations, or short channel effects. The early demonstrations of HETs suffered from poor material and interface qualities and thick device components. The revival of the HET, with a cut-off predicted frequency above 1 THz, can be correlated with the arrival of 2D materials. Here, we discuss HET operating principles, examine HET material architectures with and without tunneling barriers, and review heterostructure considerations. We discuss material and interface properties that control barrier and base performance and critically review recent 2D/3D HETs for tunneling efficiency, output current density, current gain, and output conductance. Finally, we provide an overview of 2D and 3D semiconductors that form Schottky barriers with graphene that may be utilized as a collector while considering the device physics and growth issues.