Room-Temperature WSe Impact Ionization Field-Effect Transistor Based on a Stepwise Homojunction.

The low subthreshold swing (SS) below the Boltzmann thermionic limitation (60 mV dec) is crucial for the development of power-efficient transistors. Recently, impact ionization field-effect transistors (II-FETs), which leverage carrier avalanche multiplication, have emerged as an attractive method for achieving ultra-steep SS, high on-state current density, and significant drain current on-off ratio. However, current II-FETs face challenges due to complex fabrication processes, hindering the development of future array devices. In this work, a novel II-FET is reported based on a stepwise van der Waals WSe homojunction. The device exhibits a low SS of 3.09 mV dec and a high multiplication factor exceeding 10 at room temperature. Additionally, by lowering the operating temperature, the SS can be further improved to 0.25 mV dec. Along with the improved subthreshold characteristics, the device shows a current on/off ratio >10⁵ and an on-state current density of ~1 µA µm. The findings presented here offer a promising approach to developing energy-efficient electronic devices for future technological generations.