Reconfigurable Physical Reservoir in GaN/α-InSe HEMTs Enabled by Out-of-Plane Local Polarization of Ferroelectric 2D Layer.

Significant effort for demonstrating a gallium nitride (GaN)-based ferroelectric metal-oxide-semiconductor (MOS)-high-electron-mobility transistor (HEMT) for reconfigurable operation via simple pulse operation has been hindered by the lack of suitable materials, gate structures, and intrinsic depolarization effects. In this study, we have demonstrated artificial synapses using a GaN-based MOS-HEMT integrated with an α-InSe ferroelectric semiconductor. The van der Waals heterostructure of GaN/α-InSe provides a potential to achieve high-frequency operation driven by a ferroelectrically coupled two-dimensional electron gas (2DEG). Moreover, the semiconducting α-InSe features a steep subthreshold slope with a high ON/OFF ratio (∼10). The self-aligned α-InSe layer with the gate electrode suppresses the in-plane polarization while promoting the out-of-plane (OOP) polarization of α-InSe, resulting in a steep subthreshold slope (10 mV/dec) and creating a large hysteresis (2 V). Furthermore, based on the short-term plasticity (STP) characteristics of the fabricated ferroelectric HEMT, we demonstrated reservoir computing (RC) for image classification. We believe that the ferroelectric GaN/α-InSe HEMT can provide a viable pathway toward ultrafast neuromorphic computing.