Low breakdown field and high ionization index in ReSe₂ avalanche field-effect transistors

Avalanche field-effect transistors (AFETs) based on two-dimensional (2D) materials have attracted growing interest in optoelectronics due to their enhanced performance via carrier multiplication and their potential applications in nanoelectronics. However, most AFETs employing 2D materials face challenges with high breakdown fields and low ionization indexes, which limit their applications in optoelectronics. Here, we report a ReSe₂-based AFET that achieves a breakdown electric field down to 2.55 kVcm^-1 and an ionization index up to 38.79. This performance is attributed to using anisotropic ReSe₂ as the channel material, which reduces unnecessary carrier collisions. Moreover, the incorporation of HfZrO₂ as the dielectric enhances gate modulation, which further mitigates scattering effects. The underlying mechanism is validated through calculations of electron effective masses along both in- and out-of-plane directions. Moreover, scattering probability within ReSe₂ based on simulation model and experimental data further corroborates the proposed mechanism. As a demonstration, ReSe₂ avalanche phototransistors with a high responsivity of 1.71×10⁴AW^-1 and a high gain of 173 are realized based on this platform. By incorporating anisotropic 2D materials and high-k dielectric with less carrier scattering, this AFET design provides a promising pathway for developing high-performance avalanche photodetectors.